FOUS30 KWBC 240846
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
446 AM EDT Sat Aug 24 2024

Day 1
Valid 12Z Sat Aug 24 2024 - 12Z Sun Aug 25 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST...MIDWEST...AND SOUTH FLORIDA...

...Southwest...

Another round of daytime convection is expected in the Southwest
again on Saturday, although the primary threat area should be
relatively narrow, focused in a plume of deeper moisture along the
periphery of an advancing deep trough. The Marginal Risk was
generally maintained in the same area as the previous outlook
issuance with only minor adjustments around the southern periphery.
Localized heavy downpours will remain possible given the plume of
moisture still being drawn northward out of Mexico and northward
around the western side of a sprawling upper level ridge. However,
the mid-level flow will be much stronger than usual for this time
of year helping to mitigate the flash flooding concern by providing
a strong and persistent steering flow. Nevertheless, around an
inch of rain falling in a short period of time may still lead to
flash flooding, and the Marginal Risk was maintained.

...Midwest.

A complicated forecast exists with several conditional threat
areas that still need to be sorted out. Models are generally in
good agreement in showing several rounds of elevated convection
along the periphery of a pronounced elevated mixed layer, with
700mb temperatures approaching record highs in the sounding archive
and ERA reanalysis dataset. One of the rounds is focused early in
the Day 1 period in or near Missouri. Satellite and radar imagery
from the overnight hours was showing thunderstorm development along
the Kansas/Nebraska border moving westward around the 1000-700 mb
thickness gradient and being fed by south to southwesterly winds of
35 to 50 kts per area VAD Wind profilers upstream over Kansas and
Oklahoma. The 06Z run of the HRRR continued to generate a narrow
stripe of moderate to heavy rainfall in western Kansas...its areal
coverage apparently being in check from the warm mid level
temperatures noted above but providing support to maintain the
Marginal risk area without much need to adjust the placement. The
other round looks to be focused after 00Z farther to the north from
southeast Iowa into northwestern Illinois. Ingredients favoring
heavy to excessive rainfall extend to the north and northwest in
so those solutions extending as far north and northwest into
Minnesota or southeast South Dakota cannot be ruled out yet.
Multiple hi- res models also show much of the northern sections of
the region remaining almost entirely dry. However, the risk should
an inch of rain falling in a short period of time may still lead to
flash flooding, and the Marginal Risk was maintained.be assumed to
be non- zero in the areas described above, and above 5 percent in
the Marginal Risk areas. Further updates and expansion of the
Marginal Risk is possible.

...South Florida..

Incoming deep moisture with roots from the Caribbean will make
headway into South Florida today with area precipitable water
around the 90th percentile, which is well above 2 inches. The
increasing moisture will be in proximity to a quasi-stationary
front to the north...with a sharp delineation point of where the
moisture pooling will reside. A Marginal risk area was maintained
across the Southern FL Peninsula.

Bann


Day 2
Valid 12Z Sun Aug 25 2024 - 12Z Mon Aug 26 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF NEW MEXICO AND COLORADO...AND THE MIDWEST...

...New Mexico and Colorado...

As the western periphery of the Southern Plains upper level high
begins to erode, the heavy rain threat area should expand eastward
on Sunday into more of New Mexico and Colorado. Scattered daytime
convection should develop in a plume of deeper moisture and
moderate instability, and the thunderstorms will be capable of producing
flash flooding within complex terrain and especially around any
burn scars. Hourly rain rates may locally exceed 1 inch. The
Marginal Risk was mostly maintained in the same areas.

...Midwest...

The latest guidance shows potential for for organized convection
and an associated heavy rainfall threat to persist into the Day 2
period over portions of southeast Iowa into western Illinois and
northeast Missouri. The latest CSU machine learning Excessive an
inch of rain falling in a short period of time may still lead to
flash flooding, and the Marginal Risk was maintained.
Rainfall Outlook still appeared to be displaced north and west of
where the ensembles favored heaviest rainfall...and the 00Z runs
did little to resolve the considerable degree of mesoscale
uncertainty both from the overall setup across the region. The
model consensus was best on the idea that heavy rainfall was
possible but they varied widely on placement. Therefore, the
Marginal Risk should still be viewed as the most likely placement
for heavy rain on Sunday morning, but future updates are possible.

Lamers/Bann


Day 3
Valid 12Z Mon Aug 26 2024 - 12Z Tue Aug 27 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHWEST US AND THE NORTHERN PLAINS/UPPER MIDWEST ON MONDAY...

...Southwest US...
The threat of excessive rainfall will linger into Monday across
portions of the Southwest US as precipitable water values of 0.75
to 1.00 inches remain in place from extreme southeast Arizona into
New Mexico. Scattered daytime storms remain possible within the
plume if deeper moisture...but strengthening steering flow should
help limit residence time to mitigate some of the flash flooding
concern. As mentioned earlier...though...even brief heavy rainfall
rates in a short period of time may still lead to flash flooding,
and a Marginal Risk was maintained in the region.

...Northern Plains...
An upper trough over the Intermountain region will begin lifting
northeastward across the High Plains helping to sharpen a front
across parts of the Upper Midwest/Northern Plains. Precipitable
water values are forecast to approach 1.75 inches over portions of
the eastern Dakotas prior to the arrival of the surface front and
increasing divergence/difluence associated with the upper level
system. The expectation is that moisture flux convergence along the
front will focus convection moving into an unstable environment
driven by diurnal heating that leads to locally heavy downpours.
Farther west where instability is more driven by cold mid level temperatures...rainfall should be less focused and less intense.

Bann
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FOUS30 KWBC 250838
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
438 AM EDT Sun Aug 25 2024

Day 1
Valid 12Z Sun Aug 25 2024 - 12Z Mon Aug 26 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHWEST ...

...Arizona/New Mexico and Colorado...

The axis of highest precipitable water values start the period
extending from eastern Arizona and western New Mexico into
southwest Colorado...with maximum values at or slightly above an
inch near the international border. This should help fuel
additional late day and evening convection...with at least a low-
end chance for rainfall rates that approach an inch per hour.
Flow increases across the region as the western portion of the
upper high erodes and a closed low over Nevada this morning makes
its way eastward...which should help convection be progressive
enough to mitigate at least some of the excessive rainfall threat.
Even so...even brief heavy rainfall can produce flash flooding
within complex terrain and especially around any burn scars.

...Midwest...

With the upper high/warm temperatures firmly in place and
apparently sufficiently strong to suppress buoyancy...and high
resolution models now struggling to generate more than light
showers...have removed the Marginal Risk area over portions of Iowa
and Illinois.

Bann


Day 2
Valid 12Z Mon Aug 26 2024 - 12Z Tue Aug 27 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHWEST US AND THE NORTHERN PLAINS/UPPER MIDWEST...

...Southwest US...

The threat of excessive rainfall will linger into Monday across
portions of the Southwest US as precipitable water values of 0.75
to 1.00 inches remain in place from extreme southeast Arizona into
New Mexico. Scattered daytime storms remain possible within the
plume if deeper moisture...but anomalously strong steering flow
should help limit residence time to mitigate some of the flash
flooding concern. As mentioned earlier...though...even brief heavy
rainfall rates in a short period of time may still lead to flash
flooding, and a Marginal Risk was maintained in the region.

...Northern Plains...

An upper trough over the Intermountain region will begin lifting
northeastward across the High Plains on Monday...helping to
sharpen a front across parts of the Upper Midwest/Northern Plains.
Precipitable water values are forecast to approach 1.75 inches
over portions of the eastern Dakotas prior to the arrival of the
surface front and increasing divergence/difluence associated with
the upper level system. The expectation is that moisture flux
convergence along the front will focus convection moving into an
unstable environment driven by diurnal heating that leads to
locally heavy downpours. Spread lingers in the guidance with
respect to how progressive the system will be and how much of
excessive rainfall threat will be associated with the upper system
compared to the threat associated with the convection pushing into
the better instability. Kept the westward extension introduced on Saturday...but there was a consensus that some territory could be
trimmed out near the international border.

Bann


Day 3
Valid 12Z Tue Aug 27 2024 - 12Z Wed Aug 28 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHWEST US AND THE UPPER GREAT LAKES...

...Southwest US...

The risk of excessive rainfall will linger on Tuesday afternoon and
evening across portions of the Southwest US as a moisture plume
lingers across the area and winds aloft/steering flow weakens in
response to the a mid level wave moves away over the Northern
Plains as it begins to fill. Model based ingredients suggest the
potential for locally heavy downpours may extend a bit west of the
area shown by the deterministic runs...so made a minor expansion
that way.

...Upper Great Lakes...
There is a Marginal risk of excessive rainfall over portions of the
western Great Lakes as the upper trough initially over the Upper
Midwest continues to move northeastward during the day.
Precipitable water values of 1.75 to 2 inches should already be in place
before the flow aloft becomes increasingly difluent along and
north of a quasi-stationary boundary helping enhance rainfall rates
locally. The operational guidance tended to the potential for a
couple of inches of rain...although there was considerable north-
south spread in the guidance limiting the confidence that excessive
rainfall will occur at any spot.

Bann
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FOUS30 KWBC 260833
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
433 AM EDT Mon Aug 26 2024

Day 1
Valid 12Z Mon Aug 26 2024 - 12Z Tue Aug 27 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE NORTHERN PLAINS INTO THE UPPER MISSISSIPPI VALLEY...

...Summary...
Per collaboration with WFOs ABR, FSD, MPX, and ARX, have hoisted a
Slight Risk across eastern SD into southern MN, western WI, and a
small portion of northeast IA. Have also added Marginal Risk areas
across the Mid-Upper TX Coast to eastern portions of the Hill
Country, much of the west coast of FL, and across parts of New
England.

...Northern Plains into the Upper Mississippi Valley...
An upper trough over the Intermountain region will begin lifting
northeastward across the High Plains on Monday, becoming less
amplified with time as it encounters the central U.S. ridge.
Precipitable water ahead of the upper trough and associated surface
cold front area expected to peak between 1.75-2.00 inches over the
outlook areas. Pre-frontal surface low tracking slowly from northeast NE-southwest SD early Mon to the eastern MN-western WI border by
12Z Tue will coincide with a slower eastward frontal progression
later Monday and especially Monday night. As a result expect
multiple rounds of organized convection across the outlook areas,
with multicellular upscale growth potential along with some
supercells. MLCAPEs of 3000-4000+ J/Kg this afternoon-evening within
the very moist environment will support intense instantaneous
rainfall rates; however, given the relatively weak llvl flow
compared to the mid-upper levels, expect the convection to be
forward propagating at a fairly decent clip through this evening.
This will cut down on the rainfall potential during the daylight
hours. However, given the slow moving surface low and front, again
expect another round of convection Mon night as PWs remain between
1.75-2.00 inches with MUCAPEs still between 1000-2000 J/Kg. The
aggregate of both events will likely enhance the flash flood risk
within the Slight Risk area, given the growing support from the
high-res CAMs.

Elsewhere, the Marginal Risk area remains, though did pull the
southern edge south a bit into much of southern WI (including the
MKE area) towards the max instability gradient.

...Mid-Upper TX Coast to Eastern Portions of the Hill Country...
Well defined low-mid level circulation near the TX Gulf Coast early
this morning will traverse slowly into South-Central TX this
evening and overnight. Instability will remain greatest offshore,
though SBCAPEs near 1000 J/Kg distributed in a tall/skinny profile,
with WBZ levels over 13 kft and PWs of 2.00-2.25 inches, will
produces areas of heavy rain. Given the weak deep-layer flow (0-6km
bulk shear 20kts or less), expect the more intense rainfall rates
to be short lived before the more intense updrafts collapse as the
cells become outflow dominated. Therefore have opted for a Marginal
Risk over this region, with the anticipation that any flash
flooding/short term runoff concerns will be isolated.

...Western FL Peninsula...
The guidance shows a more enhanced ECSB (East Coast Sea Breeze)
given the added synoptic low-level easterly component. This will
focus peak diurnal convective coverage along the west coast of the
FL Peninsula, which is supported by the model QPFs (especially
CAMs). PWs between 2.1-2.3 inches, along with SB CAPEs peaking
between 1500-2500 during the afternoon and early evening will
support intense short term rainfall rates. In fact, the 00Z HREF
40km neighborhood probability of 2"/hr rainfall rates climbs to
40-60% over/near the Tampa Bay area between 20-00Z (while 3"/hr
rain rates climb to around 25%). Per the CAMs, localized totals of
3-5" can be expected, much of which would be within a 3 hour
period. Cannot rule out localized flash flooding as a result,
particularly in urban areas in and around the Tampa Bay area.

...Parts of New England...
Vigorous shortwave energy and compact LFQ forcing pivoting south-
southeast on the western periphery of the upper low will set the
stage for fairly robust deep-layer forcing over a relatively narrow
corridor across parts of New England Today. The mid/upper ridge
impinging from the west is likely causing the uptick in upper level
flow (localized 90-100kt 250mb jet streak) across the Hudson
Valley/eastern NY. Steepening mid level lapse rates along with
MLCAPEs ~1000 J/Kg will help fuel numerous showers/tstms during the
peak heating hours this afternoon, with storm motions south-
southeast. The 00Z HREF depicts high probabilities of >1"/hr rates
between 18-00Z, peaking between 60-70% across eastern
CT/RI/southeast MA. Localized storm totals of 3+ inches may lead to
isolated instances of flash flooding.

...Southwest US...
The threat of excessive rainfall will linger into Monday across
portions of the Southwest US as precipitable water values of 0.75
to 1.00 inches remain in place from extreme southeast Arizona into
New Mexico. Scattered daytime storms remain possible within the
plume if deeper moisture...but anomalously strong steering flow
should help limit residence time to mitigate some of the flash
flooding concern. As mentioned earlier, although even brief heavy
rainfall rates in a short period of time may still lead to flash
flooding, and a Marginal Risk was maintained in the region.

Hurley


Day 2
Valid 12Z Tue Aug 27 2024 - 12Z Wed Aug 28 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE SOUTHWEST AND UPPER MIDWEST...

...Summary...
Have expanded the Marginal Risk southward across the Upper Midwest,
to account for the potential of locally heavy rainfall before the
frontal passage.

...Upper Midwest-Upper Great Lakes...
Upper shortwave will continue to dampen somewhat by Day 2, which
will weaken the deep-layer Qs forcing. Prior to the surface frontal
passage, PWs will remain between 1.75-2.00 inches (around 2
standard deviations above normal). Instability will be much greater
over the southern portion of the outlook area (down towards the
I-80 corridor, which was a big reason to nudge the ERO Marginal
Risk farther south (matching up with SPC's Day 2 Severe Slight
Risk). Expect the activity to move rather swiftly before dropping
south of the outlook area Tue night. Still appears to be a
localized flash flood risk though, given the weakening deep-layer
forcing and degree of downwind propagation. Therefore, have
continued with the Marginal Risk.

...Southwest US...
The risk of excessive rainfall will linger on Tuesday afternoon
and evening across portions of the Southwest US as a moisture plume
lingers across the area and winds aloft/steering flow weakens in
response to the a mid level wave moves away over the Northern
Plains as it begins to fill. Model based ingredients suggest the
potential for locally heavy downpours may extend a bit west of the
area shown by the deterministic runs...so made a minor expansion
that way.

Hurley
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FOUS30 KWBC 270841
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
441 AM EDT Tue Aug 27 2024

Day 1
Valid 12Z Tue Aug 27 2024 - 12Z Wed Aug 28 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE SOUTHWEST AND UPPER MIDWEST...

...Summary...
Compared to yesterday's Day 2 ERO, we have expanded the Marginal
Risk area to include much of the Upper to Mid MS Valley, along with
parts of the Lower MO Valley. Only minor tweaks were made to the
Marginal Risk area across the Southwest.

...Lower Missouri Valley-Mid to Upper Mississippi Valley-Upper
Great Lakes...
Upper shortwave over the Northern Plains early this morning will
continue to dampen somewhat during the day, which in term will
weaken the deep-layer Qs forcing. By the same token, as the
shortwave becomes sheared, the confluence aloft will sharpen a
compact upper level jet streak (90-100 kts) in the lee of the
flattening shortwave, thereby increasing the Qn forcing within the
right entrance region (strengthening the low-level frontogenesis).
The guidance, including the CAMs, appears to be having a tough time
resolving this transition of favorable dynamical forcing. The
ensemble of model QPFs show a bimodal distribution with the max
rainfall axes -- one to the north (central MN-northern WI-Upper
MI), behind Monday night MCS, where the DPVA/Qs forcing is most
favorable, and another farther south (northeast KS/southeast NE,
southern IA, central-northern MO, much of IL-IN), where the uptick
in right entrance region forcing (upper divergence and low-level
frontogenesis) coincides with a more moist and unstable
environment. TPWs climbing between 1.8-2.1 inches over this
southern portion, along with ML CAPEs of 1500-2500+ J/Kg, will
support locally intense shorter-term rainfall rates. Moreover, as
the front flattens (becomes more W-E oriented), more parallel to
the mean 850-300 mb flow, suspect cell training will become a
greater risk. What will likely keep this event from needing a
Slight Risk is the relatively weak low-level inflow. The mean flow
is fairly weak as well (850-300 mb wind 15-20 kts), however there
is sufficient shear to keep any organized segments forward
propagating.

Farther north, the instability won't be as robust, however the
soils will have already been primed from the MCS Monday night.
Therefore with this secondary max QPF axis that the 00Z CAMs are
depicting, another round of heavy rainfall could lead to isolated
flash flooding given the antecedent wet soils and reduced FFG.

...Southwest US...
The risk of excessive rainfall will linger on Tuesday afternoon
and evening across portions of the Southwest U.S., as the moisture
plume lingers across the area and winds aloft/steering flow
weakens in the wake of the departing Northern Plains shortwave. PWs
peaking around 1.3 to 1.4 inches (1.5 to 2 standard deviations
above normal for late August), along with MLCAPEs of 500-1000 J/Kg,
will support isolated hourly rain rates of 0.75-1.00" underneath
the strongest convective cores. The 00Z HREF probabilistic
guidance depicts this, with the risk spreading a bit farther west
(into eastern AZ) compared to yesterday. Have maintained the
Marginal Risk in the Day 1 ERO given the continued localized flash
flood threat during the peak heating hours (afternoon/evening).
evening.

Hurley


Day 2
Valid 12Z Wed Aug 28 2024 - 12Z Thu Aug 29 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHWEST, NORTHERN PLAINS TO UPPER MISSISSIPPI VALLEY, AND
PARTS OF THE MIDWEST INTO THE OHIO VALLEY AND NORTHERN MID-ATLANTIC...

...Summary...
Compared to yesterday's Day 3 ERO, the Southwest and northern-tier
Marginal Risk areas were largely unchanged. However, based on the
00Z guidance suite, the Marginal Risk across the northern Mid
Atlantic Region was expanded westward to include much of the OH
Valley and parts of the Mid MS Valley.

...Southwest...
Guidance mid-level vorticity progs continue to support a more
north-south outlook area compared to Day 1, though nonetheless
still quite similar. Instability and moisture parameters (afternoon
and evening CAPE and PW profiles) remain similar, and thus the
anticipation of more isolated/localized instances of flash flooding
than otherwise, particularly after 18Z coinciding with peak
diurnal heating.

...Upper Midwest...
Strong, deep-layer warm and moisture advection ahead of the next
vigorous mid-upper level trough (closed 500-300 mb low) and
associated surface fronts will favor more organized/widespread
elevated convection by Wed night ahead of the advancing low-level
warm front. Models are still indicating spread with the QPFs,
enough to keep the ERO risk level at Marginal for now. Later
shifts will need to assess the need to upgrade at least a portion
of the outlook area to Slight however, as the heavy rainfall signal
exists given the degree of dynamical forcing and thermodynamical
profiles. 00Z ECMWF and regional GEM in fact indicates localized
totals of 3+ inches between 00-12Z Thu.

...Eastern Portions of the Mid Mississippi Valley-Ohio Valley-
Northern Mid Atlantic...
W-E frontal boundary will sink southward on Wednesday, then remain quasi-stationary Wed night as the mid- upper trough traverses the central-northern Rockies and High Plains. Deep-layer moisture and
instability will be sufficient for areas of heavy rainfall along
this boundary, while the easterly storm motions (parallel to the
low-mid level fronts) would support the risk of cell training.
Outside of the 00Z Regional GEM, the guidance at this point isn't
overly robust with the QPF within the outlook area, at least not
yet, despite some uptick in right- entrance region forcing from the
upper level jet streak over northern NY-New England. Thus for now,
have kept the ERO risk at Marginal.

Hurley


Day 3
Valid 12Z Thu Aug 29 2024 - 12Z Fri Aug 30 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM PARTS OF THE
CENTRAL PLAINS INTO THE UPPER MIDWEST, ALONG WITH THE MID ATLANTIC REGION...

...Summary...
Few changes were made to yesterday's Day 4 ERO Marginal Risk areas
across the Central Plains to Upper Midwest and over the Mid
Atlantic.

...Eastern Portions of the Central Plains into the Upper Midwest... Aforementioned upper trough and associated surface cold front will
continue eastward on Thu-Thu night, though with the mid-upper low
lifting north into western Ontario by 12Z Fri. This will keep the
bulk of the deep-layer forcing north of the U.S., however
sufficient low-level frontogenesis will persist ahead of the mid-
upper shortwave well south of the main mid-upper low. Much
cooler/drier post-frontal airmass will lead to a fairly tight
moisture gradient along the front, with strengthening negative PW
advection behind it. Given the anticipated swift movement of the
front (strong deep-layer shear), for now it would appear any
organized, more widespread linear convective segments ahead of the
front will too be rather progressive. Therefore, have maintained
the Marginal Risk area.

...Mid Atlantic Region...
Lingering quasi-stationary boundary across the Mid Atlantic will
couple with increasing right entrance region forcing via an upper
level jet streak traversing NY-New England. Over time, the CAD
signature becomes evident from the guidance -- i.e. cooler/more
stable low-level air and a south-southwest dip in the surface
boundary occur along and near the Mid Atlantic Coast. However
plenty of deep-layer instability should linger west of the
DelMarVa, which along with the forcing, should allow for more widespread/organized convection and a localized flash flood threat.

Hurley
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FOUS30 KWBC 280829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Wed Aug 28 2024

Day 1
Valid 12Z Wed Aug 28 2024 - 12Z Thu Aug 29 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHWEST, NORTHERN PLAINS TO UPPER MISSISSIPPI VALLEY, AND
PARTS OF THE MIDWEST INTO THE OHIO VALLEY AND NORTHERN MID-ATLANTIC...

...Summary...
Few changes were made to yesterday's Day 2 ERO Marginal Risk
areas.

...Southwest...
Guidance mid-level vorticity progs continue to support a more
north-south outlook area compared to Day 1, though nonetheless
still quite similar. Instability and moisture parameters (afternoon
and evening CAPE and PW profiles) remain similar, and thus the
anticipation of more isolated/localized instances of flash flooding
than otherwise, particularly after 18Z coinciding with peak
diurnal heating.

...Eastern Dakotas-Western Minnesota...
Strong, deep-layer warm and moisture advection ahead of the next
vigorous mid-upper level trough (closed 500-300 mb low) and
associated surface fronts will favor more organized/widespread
elevated convection by Wed night ahead of the advancing low-level
warm front. After 00Z, 850 mb southerly flow increases to 40-50 kts
from west to east across the outlook area, which is around 4
standard deviations above normal per the SREF and GEFS. Not
surprisingly, 850-700 mb moisture flux anomalies also climb to +3
to +4. Given the strength of the low-mid layer moisture transport
and uptick in IVT, isolated QPF totals of 3-5" per some of the 00Z
CAM runs should not come as a surprise. However, at least for now,
reasons for keeping the ERO below the Slight threshold over this
region Wed night include (a) the continued high spread in guidance
QPFs (including CAMs), along with (b) progressive southeast motion
of the convection growing upscale (MCS) per the forecast Corfidi
Vectors, given the shear between the low-level flow and mean
850-300 mb wind.

...Eastern Portions of the Mid Mississippi Valley-Ohio Valley-
Northern Mid Atlantic...
W-E frontal boundary will sink southward on Wednesday, then remain quasi-stationary Wed night as the mid-upper trough traverses the central-northern Rockies and High Plains. Deep-layer moisture and
instability will be sufficient for areas of heavy rainfall along
this boundary, while the easterly storm motions (parallel to the
low-mid level fronts) would support the risk of cell training,
especially when the Corfidi Vectors drop to 5 kt or less). WPC QPF
and smart blends (NBM and HREF) have come up from the previous
forecast, with the D1 period now fully within the high-res CAM
window. Uptick in right-entrance region forcing (upper divergence...
low-level FGEN) from the upper level jet streak over northern NY-
New England will favor more widespread convection, especially when
coinciding with peak diurnal heating. However, lack of robust low-
level moist inflow/transport will likely not sustain/prolong strong
updrafts and intense hourly/sub-hourly rainfall rates. As a
result, have maintained the Marginal Risk from yesterday's Day 2
ERO, albeit with a few tweaks based on the latest guidance trends.

Hurley


Day 2
Valid 12Z Thu Aug 29 2024 - 12Z Fri Aug 30 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PARTS OF THE
LOWER MISSOURI VALLEY INTO THE UPPER MISSISSIPPI VALLEY...

...Summary...
The biggest change from yesterday's Day 3 ERO was to upgrade a
portion of the Marginal Risk to Slight across parts of the Lower MO
Valley into the Upper MS Valley. Have also added a Marginal Risk
across the central-western LA and Middle-Upper TX Gulf Coast.

...Lower MO Valley and Corn Belt into the Upper MS Valley...
Aforementioned upper trough and associated surface cold front will
continue eastward Thu-Thu night as the mid-upper low lifting north
into western Ontario by 12Z Fri. Given the progression of synoptic
features, the bulk of the deep-layer forcing and more anomalous
low-level inflow/moisture flux will pivot across the Upper MS
Valley and southern Canada. Compared to the southern portions of
the Slight Risk area, generally speaking instability will not be
as high over the northern portion (i.e. along the path of the
triple point). However, owing largely to the SSW LLJ, especially as
it becomes more aligned with the mean 850-300 mb flow, the
eastward progression of the quasi-linear convective segments will
slow during the period as per the weakening Corfidi Vectors
(decreasing forward propagation). Therefore the risk for cell
training will increase along and ahead of the front.

Farther south (IA and eastern NE), the pre-frontal activity should
be more forward-propagating, however much higher deep-layer
instability south of the triple point, especially by late Thu-Thu
night, will maintain the risk of more intense hourly rainfall
rates (1.75-2.00+ inches) a little while longer (beyond 00Z Fri)
per the 00Z HREF exceedance probabilities.

...Mid Atlantic Region...
Lingering quasi-stationary boundary across the Mid Atlantic will
couple with increasing right entrance region forcing via an upper
level jet streak traversing NY-New England. Over time, the CAD
signature becomes evident from the guidance -- i.e. cooler/more
stable low-level air and a south-southwest dip in the surface
across MD-VA. However plenty of deep-layer instability should
linger west of the DelMarVa, especially west of I-95, which along
with the forcing, should allow for more widespread/organized
convection and a localized flash flood threat.

...Louisiana and Middle-Upper Texas Coast...
Underneath the broad upper ridge, models show a subtle mid-upper
level shortwave lifting gradually northward toward the central-
western LA Coast on Thu. Subtle upper-level forcing (DPVA/upper
divergence) along with persistent (albeit not overly robust) low-
level moisture transport from the GOMEX will make for a localized
flash food risk, especially coinciding with peak diurnal heating
Thu afternoon. PW values increasing to 2.3-2.4 inches along with
MLCAPEs between 1000-2000 J/Kg (tall/skinny distribution) and WBZ
heights climbing to aoa 15,000 feet will establish an optimal
thermodynamic profile for heavy rainfall. Sub-hourly rainfall rates
of 2-3" will be possible underneath the strongest cores. By the
same token, 0-6km bulk shear generally 20kts or less will lead to
more pulse-type convection and thus more short-lived intense
rainfall rates. Still enough of a flash flood risk to support a
Marginal Outlook area in the ERO, especially given the uptick in
southeasterly low-level flow from the Gulf on Thursday, which
would be of equal or greater magnitude compared to the 850-300 mb
wind. Corfidi Vectors aligning in the opposite direction than the
inflow would support increased upwind propagation and cell
training.

Hurley
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FOUS30 KWBC 290823
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
423 AM EDT Thu Aug 29 2024

Day 1
Valid 12Z Thu Aug 29 2024 - 12Z Fri Aug 30 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE UPPER MIDWEST AND THE MID ATLANTIC AS WELL AS ALONG THE GULF COAST...

Lower Missouri Valley to the Upper Midwest...

Height falls associated with an upper trough and surface cold
front will continue eastward today and tonight as a deep mid-
upper low lifts north into western Ontario by 12Z Fri. Given the
progression of synoptic features, the bulk of the deep- layer
forcing and more anomalous low-level inflow/moisture flux will
pivot across the Upper MS Valley and southern Canada. HREF
neighborhood probabilities for greater than 2 inch and greater than
3 inch amounts remain fairly aggressive (40-70%) within the
previously issued Slight risk area with the core of the potential
being located over parts of Iowa and southern Minnesota. As
mentioned before...this area has been dry as of late, so some of
the precip will be beneficial, but anomalous moisture and strong
mid- level ascent could generate rainfall rates capable of
flooding, especially within any urban footprint.

Mid Atlantic Region...

Maintained the Slight risk area across the VA Piedmont down into
portions of Southeast VA and as far north as the WV/MD/PA line with
only minor modifications. There will be a fairly well-depicted
axis of low- level instability and anticipated surface convergence
in proximity to a backdoor front settling in to the area. A core
of elevated theta-E will align with the front from northwest to
southeast during the afternoon hours while a jet streak to the
northeast catches the Central Mid Atlantic just within the right-
entrance region of the jet leading to appreciable upper forcing
during peak destabilization. Convective activity is expected to initiate
across the Blue Ridge and adjacent Appalachian Front then drift
eastward. various CAMs and global guidance. MLCAPE between
2500-3500 J/kg will be common within the vicinity of the front, so
ample surface based instability will be present to maximize
potential of any thunderstorm development.

Louisiana and Middle-Upper Texas Coast...

Models show a subtle mid-upper level shortwave lifting gradually
northward toward the central- western LA Coast today and tonight.
Subtle upper- level forcing along with persistent (albeit not
overly robust) low- level moisture transport from the Gulf of
Mexico will result in a localized flash food risk, especially
coinciding with peak diurnal heating . Precipitable water values
increase to 2.3-2.4 inches along with MLCAPEs between 1000-2000
J/Kg and WBZ heights climbing to aoa 15,000 feet will establish an
optimal thermodynamic profile for heavy rainfall as shown in the
NAM and ARW guidance. This should result in rainfall rates of 2-3
inch on a sub-hourly time scale will be possible underneath the
strongest cores. Given that the overall forecast reasoning has not
changed and the latest and the latest guidance continues to show 3
to 5+ inch amounts hugging the coastline...saw little reason to
make more than minor nudges to the Slight risk and Marginal risk
areas.

Bann


Day 2
Valid 12Z Fri Aug 30 2024 - 12Z Sat Aug 31 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG THE IMMEDIATE
GULF COASTAL AREAS OF SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA ...

Gulf Coast...

There is a Slight Risk of excessive rainfall along the immediate
Gulf coast region of southeast Texas into a small portion of
adjacent Louisiana...with a Marginal risk area extending as far
north as the upper Great Lakes in response to gulf moisture
streaming northward ahead of a well-defined cold front advancing
eastward. In addition...a well defined circulation that has
persisted a couple of days over the Gulf of Mexico and Texas will
meander eastward into Arkansas. While its impact will be waning as
the system fills...it still could allow for additional convective
flare-ups along and near the Gulf of Mexico. Precipitable water
values of 2 to 2.25 inches are widespread from eastern Texas into
Louisiana and Arkansas with an axis then extending north and east
ahead of the front being some 2 to 2.5 standard anomalies above
climatology being an indication of the moisture-laden atmosphere
still in place. Discrepancies linger in the guidance on placement
and amounts in where the deepest moisture gets funneled...with the
above- mentioned upper level feature playing a key role. Between
the NBM still showing 2 to 4+ inch amounts along the southeast
Texas coast on Day 2 alone and a more than 6 inches for a 2-day
total in proximity to the 28/12Z guidance and already covered by
yesterday's Day 3 outlook...saw little reason to make any changes
to the Slight Risk area.

Great Lakes to Southern Rockies/Southern High Plains...

Convection will continue to be driven by deep gulf moisture that is
initially drawn northward and then northeastward towards the Great
Lakes ahead of a well defined cold front pushing southward and
eastward. By 00Z Saturday...moisture anomalies of 2 standardized
anomalies will be in place. The overall upper forcing still does
not appear to be terribly robust but the diurnal instability
supports at least the potential for locally excessive rainfall.

Bann


Day 3
Valid 12Z Sat Aug 31 2024 - 12Z Sun Sep 01 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG A SMALL
PORTION OF THE UPPER TEXAS COAST AND ADJACENT COASTAL LOUISIANA...

There is a Slight risk of excessive rainfall once again over
portions of the Upper Texas coast and adjacent portions of
Louisiana with a broad Marginal risk are extending northward and
eastward as gulf moisture streams northward ahead of...and
eventually intersects with...a cold front. The 29/00Z suite of
guidance focuses highest rainfall amounts from Saturday into early
Sunday over portions of the Upper Texas coast and nearby Louisiana
where a moisture plume with precipitable water values in excess of
2.25 inches should be positioned at the start of the period (a
nearly 2.5 standardized anomaly greater than climatology for this
time of year and above the 90th climatological percentile along the
gulf coastline shown by both the ECENS and GEFS). Two inch
precipitable water values are forecast to extend from eastern Texas northeastward in a corridor to far southern Indiana. During the
ensuing 24 hours...the northern portion of the front reaches
portions of New England and the Mid-Atlantic region but the
southern portion of the front makes little progress into Texas and
Arkansas. Expectations are that downpours will be possible along
and ahead of the front. Given the amount of moisture and weaker
steering flow, though, the southern portion of the Marginal area
has a better chance for excessive rainfall while storms to the
north should be more progressive leading to a nominally low/more
isolated excessive rainfall risk. The question remains whether or
ot the stronger dynamics farther north will enhance amounts/rates.
Will leave as a Marginal risk area for the time being in deference
to the NBM amounts and guidance from the CSU ML EROs.

Bann
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FOUS30 KWBC 300826
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
426 AM EDT Fri Aug 30 2024

Day 1
Valid 12Z Fri Aug 30 2024 - 12Z Sat Aug 31 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG THE IMMEDIATE
GULF COASTAL AREAS OF SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA...

...Gulf Coast...

Moderate to heavy rainfall expected along the Gulf coast as deep
moisture advects northwards as a tropical low drifts in the
northwest portions of the Gulf of Mexico. Repeated rounds of slow-
moving heavy rain cells from the Gulf into the Texas/Louisiana
border area east of Houston. Guidance depict 1 to 4 inches for
areal average along the coast with isolated higher amounts
possible. Some of the hi-res guidance have very isolated maximums
of 6 to 11 inches. Areal averages of The focus for any potential
flooding in this small area will be mainly in the urban areas
around Beaumont/Port Arthur and points east. A Slight Risk is in
effect from the Houston area east to Vermillion Bay. The
surrounding Marginal risk was expanded to include areas near/west
of Mobile.

...Great Lakes to Southern Rockies/Southern High Plains...

Convection will continue to be driven by deep gulf moisture that
is streaming into the north/northeast towards the Great Lakes
ahead of a well defined cold front pushing southward and eastward.
Precipitable water values of 2 to 2.25 inches are widespread from
eastern Texas into Louisiana and Arkansas with an axis then
extending north and east ahead of the front being some 2 to 2.5
standard anomalies above climatology being an indication of the
moisture-laden atmosphere still in place. There continues to be
some variance on where the deepest moisture gets funneled... with
the above- mentioned upper level feature playing a key role.
Although the overall upper forcing still does not appear to be
terribly robust, the diurnal instability supports at least the
potential for locally excessive rainfall. A broad Marginal Risk was
maintained for this period from New Mexico/Texas to Wisconsin/New
York.

...Mid-Atlantic...

Portions of the region will have PW values greater than 2 inches
along with slow moving storms near the front. This environment
looks to be quite favorable for localized heavy rain with some of
the guidance showing probabilities of 3 inches/3 hour 30-50%
across Northeast North Carolina. A Marginal Risk area was raised
for portions of southeast Virginia and northeast North Carolina.

Campbell


Day 2
Valid 12Z Sat Aug 31 2024 - 12Z Sun Sep 01 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG A SMALL
PORTION OF THE UPPER TEXAS COAST AND ADJACENT COASTAL LOUISIANA...

...New Mexico and Texas...

Showers and thunderstorms are expected to fire across portions of
New Mexico and Texas as the trailing cold front slows its
progression over the region. Some of these storms will be capable
of producing hourly rain rates greater than 0.50/1 inch per hour.
A Marginal Risk area was maintained for this part of the country.

...Gulf Coast...

Showers and thunderstorms will persist along the Gulf coast along
the nearly stationary tropical low and frontal boundary. The Slight
Risk area that was in effect has bee maintained as well as expanded
eastward to just east of Vermillion Bay. A broad Marginal risk area
extends northward and eastward as gulf moisture streams northward
ahead of...and eventually intersects with...a cold front. Guidance
shows the highest amounts occurring from Saturday into early
Sunday over portions of the Upper Texas coast and nearby Louisiana
where a moisture plume with precipitable water values in excess of
2.25 inches should be positioned at the start of the period (a
nearly 2.5 standardized anomaly greater than climatology for this
time of year and above the 90th climatological percentile along the
gulf coastline shown by both the ECENS and GEFS).

...Lower Mississippi Valley to New England...

Two inch precipitable water values are forecast to extend from
eastern Texas northeastward in a corridor to far southern Indiana.
During the ensuing 24 hours...the northern portion of the front
reaches portions of New England and the Mid-Atlantic region but the
southern portion of the front makes little progress into Texas and
Arkansas. Moderate to heavy rain will be possible for areas along
and ahead of the advecting boundary.

Given the amount of moisture and weaker steering flow, though, the
southern portion of the Marginal area has a better chance for
excessive rainfall while storms to the north should be more
progressive leading to a nominally low/more isolated excessive
rainfall risk. The question remains whether or ot the stronger
dynamics farther north will enhance amounts/rates. Some of the
guidance do signal a concentration of QPF and increasing threat for
excessive rainfall over portions of central pennsylvania.
Antecedent conditions will have lowered FFGs across this part of
the region thus becoming more favorable for growing flooding
concerns. After coordination with the local forecast office decided
to hold off for another cycle to reassess the need for a possible
upgrade to a Slight Risk for central portions of Pennsylvania.

Campbell/Bann


Day 3
Valid 12Z Sun Sep 01 2024 - 12Z Mon Sep 02 2024

...New Mexico and Texas...

Showers and thunderstorm activity is expected to linger with the
capability of producing excessive rainfall. The threat for
localized flood concerns will remain elevated thus a Marginal Risk
was maintained for this period.

...Gulf Coast...

The highest rainfall in this multi-day heavy rain event will have
likely already occurred however showers and thunderstorms are
expected to linger over the region near the coastline. A Marginal
Risk remains in affect from the southeast Texas coastline to
eastern Louisiana coastline.

...Eastern Tennessee Valley and Mid-Atlantic region...

Moderate to locally heavy rainfall will persist across portions of
the Mid-Atlantic as a cold front approaches the region. Some of
these areas will have lowered FFGs by this period and may be more
susceptible for additional rainfall to increase the threat for
local flooding concerns. A Marginal Risk area was maintained from
eastern Tennessee Valley to the Mid-Atlantic region.

Campbell
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FOUS30 KWBC 310823
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
423 AM EDT Sat Aug 31 2024

Day 1 Valid 12Z Sat Aug 31 2024 - 12Z Sun Sep 01 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE GULF COAST
FROM GALVESTON TEXAS THROUGH THE MISSISSIPPI COAST AS WELL AS FOR
THE CENTRAL APPALACHIANS...

...Texas to the Mid-Atlantic and New England...

A slow-moving cold front over the Midwest will move into the
central Appalachians this afternoon. Surface dew points in the 60s
and rising precipitable water values to around 1.75 inches (+2
sigma or 98th percentile) will support both a severe weather threat
(see SPC outlook) and a heavy rain threat. Though convection
should be progressive with the front (or pre-frontal trough), FFG
values are around 1-2"/hr and 00Z HREF neighborhood probs show
values rising to 40-80% for >1"/hr and 10-40% for >2"/hr. Focus of
highest threat will lie from eastern WV northward through central
PA and into the Southern Tier of NYS where the complex terrain can
add to the flash flooding sensitivity coincident with slightly
higher than average soil moisture. Maintained the Slight Risk from
the previous forecast with little change in shape. Along the front
in general, a Marginal risk was maintained from New England back
through the mid-MS Valley/Mid-South into TX where convection will
be a bit less coherent and the threat for any flash flooding will
be lower, but non-zero.

...Central Gulf Coast...
Decaying mid-level vort max will drift eastward along the coast,
detached from any surface trough just offshore. However, in-situ
moisture remains highly anomalous -- precipitable water values
around 2.25 inches which is about +2 to +3 sigma. Most of the hi-
res guidance keeps the heaviest rainfall today along and just off
the coast but hint at drawing some heavier cores inland a bit
toward the I-10 corridor in LA. Maintained the Slight Risk outline
for southern Louisiana given the continued threat of heavier rain
today.

...Florida...
Above normal moisture (PW > 2") will linger over southeast FL
where afternoon convection could support some local downpours
(2-3"/hr rates) that may induce some flooding over the urban areas
from ~PBI to MIA/HST and perhaps into the Keys.

...Arizona...
Added a Marginal Risk for the Mogollon Rim as a weak mid-level
vort center pushes through the region. Though precipitable water
values are around normal, sufficient instability this afternoon
could support some isolated heavier rain cores with 1"/hr rates.

Fracasso


Day 2 Valid 12Z Sun Sep 01 2024 - 12Z Mon Sep 02 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
NEW MEXICO/TEXAS, THE NORTHERN GULF COAST, AND THE MID-ATLANTIC...

...Southeastern New Mexico and West Texas...
250mb upper trough moving out of northern Mexico and southern
AZ/NM and mid-level vort max (perhaps weakly closed low) will creep
closer to far western Texas day 2. Sufficient moisture (though
near normal) will be in place over the region to sustain some
isolated excessive rainfall via afternoon convection.

...Gulf Coast...
Meandering weakness in the mid/lower-levels will again help drive
some heavier rainfall along the Upper TX Coast into southern
Louisiana. Maintained a Marginal Risk for now given the uncertainty
in the day 1 period with respect to heavier rain placement (on or
offshore) and amounts. Again, the highest rainfall may linger just
off the coast but potential is certainly there to nudge inland.

...Eastern Tennessee Valley and Mid-Atlantic region...
Cold front will continue to push through the area to the east and
south, squeezing the best forcing into southern Virginia and into
North Carolina where afternoon convection may yield 1-2" amounts
and a localized threat of flash flooding. There and to the west
over western VA into WV, FFG guidance is lower and some lingering
rain may eclipse those values as the front works through.

Fracasso


Day 3 Valid 12Z Mon Sep 02 2024 - 12Z Tue Sep 03 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR TEXAS AND
THE CAROLINAS...

...Texas...
Mid-level vort and upper trough will move into West Texas on
Monday atop increased moisture from the southeast. Guidance
continues to show modest QPF of 1-5" in various locations but the
spread is quite large -- nearly covering the whole state in their
QPF max region among the deterministic, ensemble, and AI guidance.
The CSU machine learning first guess fields suggest a broad Slight
Risk over the Hill Country which is, perhaps, a best consensus
placement, but prefer to hold off an upgrade to a Slight Risk for
now until at least the ensembles come into better agreement.

...Carolinas...
Cold front will sink into the Carolinas which will nudge the
excessive rainfall threat south from day 2. Best dynamics move
offshore with the trough axis but the Marginal Risk should cover
any isolated flooding threat due to afternoon convection.


Fracasso
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FOUS30 KWBC 010838
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
438 AM EDT Sun Sep 1 2024

Day 1
Valid 12Z Sun Sep 01 2024 - 12Z Mon Sep 02 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
NEW MEXICO/TEXAS, THE NORTHERN GULF COAST, AND THE MID-ATLANTIC...

...Southeastern New Mexico and West Texas...

An approaching 250 mb upper trough will move into far West Texas
today while a surface boundary lingers across the Hill Country.
Precipitable water values are forecast to be around 1.5-1.75" which
is about +1 to +2 sigma with the typical NW to SE gradient.
Afternoon convection should percolate today and could fall over
areas that have seen a few inches of rain on Saturday (with lower
FFG values as a result). Coverage should be somewhat isolated so
the Marginal Risk will suffice.

...Gulf Coast...

Meandering weakness in the mid-lower levels will again help drive
some heavier rainfall along the Upper TX Coast into southern
Louisiana. Maintained the Marginal Risk as the bulk of the guidance
keeps the heaviest rain offshore, though it will be close (again)
just like on Saturday.

...Eastern Tennessee Valley and Mid-Atlantic Region...

A cold front will approach the Appalchians this afternoon as the
lead boundary dissipates, leaving a trough over the coastal plain.
The best forcing for afternoon convection will lie there, generally
over far southeastern Virginia into central/eastern North Carolina.
00Z HREF probs of exceeding FFG values are around 10-20% (via 1-2
inch per hour rates), though there are hints at some higher rates
still. Activity should be mostly progressive, suggesting a
localized threat of flash flooding. Kept the Marginal Risk for this
area.

Fracasso


Day 2
Valid 12Z Tue Sep 03 2024 - 12Z Wed Sep 04 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
HILL COUNTRY OF TEXAS...

...Texas...

Mid-level vort and upper trough will move into West Texas on
Monday atop increased moisture from the southeast. Guidance
continues to show modest QPF of 1-5 inches near and around the Hill
Country, with various foci in the deterministic models. ECMWF-AIFS
was still decidedly north compared to the other models. The CSU
machine learning first guess fields still suggest a broad Slight
Risk over the Hill Country, so at least there is some consistency
over the past 24-36 hours in this guidance vs the models (which is
the point). FFG values are lowest near/south of San Angelo to Del
Rio (due to recent rain) where the HREF probs of exceeding these
values reach ~50%.

...Carolinas...

Cold front will sink farther into the Carolinas from day 1, which
will nudge the excessive rainfall threat south as well. Best
dynamics move offshore with the trough axis so the Marginal Risk
should cover any remaining isolated flooding threat due to
afternoon convection.

Fracasso


Day 3
Valid 12Z Tue Sep 03 2024 - 12Z Wed Sep 04 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR TEXAS...

...Texas...

Mid-level vort will be exiting the region though precipitable
water values will remain high (+1 to +2 sigma initially, then
decreasing late Tuesday). Depending on how much (and where) rain
falls on day 2, there is room to upgrade some of this region to a
Slight Risk pending better model agreement in future runs. For now,
ensemble consensus is just east of the Hill Country but individual
models are quite varied north/south. First guess fields from the
CSU machine learning algorithm do show a Slight Risk outline,
lending credence to a future upgrade.

Fracasso
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FOUS30 KWBC 020830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
430 AM EDT Mon Sep 2 2024

Day 1
Valid 12Z Mon Sep 02 2024 - 12Z Tue Sep 03 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE HILL COUNTRY/CENTRAL TEXAS AND ALONG THE TEXAS GULF COAST...

...Texas...

An upper level trough with a mid-level vort will be advancing into
western Texas during this period. Meanwhile a surface low hugging
the South Texas Coast will maintain easterly flow from the Gulf
allowing PW values of 2+ inches to pool over much of the state. The
latest guidance continues to depict areal averages of 1 to 5 inches
of QPF across the Hill Country into east-central Texas and along
much of the Texas coastline. Recent rainfall has increased soil
saturation across the state thus lowering FFGs. The hi-res guidance
is showing training of slow moving convection capable of 1 to 2.5
inches/hour rain rates which could easily lead to scattered areas
of excessive rainfall and localized flash flooding. A Slight Risk
areas remains in effect for west-central and central Texas.
Additionally, a Slight Risk was added for the coastline today where
storms will be producing rates of 1 to 3 inches/hour.

...Carolinas...

A cold front sinking through the Mid-Atlantic region will continue
to move showers and thunderstorms southward over the Carolinas
today. Guidance keeps the bulk of the QPF offshore during this
period where there are better dynamics in place however there will
still be an isolated threat for localized excessive rainfall and
flooding. A Marginal Risk area was maintained for eastern portions
of the Carolinas.

Campbell


Day 2
Valid 12Z Tue Sep 03 2024 - 12Z Wed Sep 04 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CENTRAL TEXAS...

...Texas...

The mid-level vort is expected to exit the region although
precipitable water values will remain high (+1 to +2 sigma
initially, then decreasing late Tuesday). A large portion of the
flooding potential will be contingent on a verified forecast from
Day 1/Monday, as Monday will have the heavier rain/stronger storms
of the two days. However, even the lesser amounts of rain expected
Tuesday should still cause flooding issues in the area with a
widespread 1 to 1.5 inches forecast with locally higher amounts. A
Slight Risk remains in effect for central portions of the state.

The heaviest rains in the state are expected to be along the Gulf
Coast from Galveston south and west through Corpus Christi. Locally
heavy rains to 2 inches per hour will be possible. For now the
greatest flooding threat remains confined to any urban areas, but
should Monday's rains overperform here then a Slight may be needed
for the hardest hit areas with future updates.

...Idaho/Montana...

A potent shortwave trough will interact with up to 2 sigma above
normal atmospheric moisture on Tuesday. PW values rising to near 1
inch will support storms capable of heavy rain that may produce
isolated flash flooding should the storms impact particularly flood
sensitive or more urban areas.

Campbell/Wegman


Day 3
Valid 12Z Wed Sep 04 2024 - 12Z Thu Sep 05 2024

...Gulf Coast and Lower Mississippi Valley...

The influx of anomalous Gulf Moisture will persist all across the
southern tier states while the upper trough and vort exits the
plains and into the Mississippi Valley. The surface front will
continue to be draped west to east across the South continuing to
provide focus for showers and thunderstorms across the region.
During the late afternoon and evening hours there will be an
intensification of instability and forcing to boost rainfall rates
across the Lower Mississippi Valley, particularly over Louisiana,
western Mississippi and southeast Arkansas. Most of the guidance
are suggesting that 1 to 3 inches will concentrate over this part
of the region thus increasing the risk for excessive rainfall and
local flooding potential. There is the potential for a few
locations for local maximums to exceed 6 inches near northern Louisiana/Arkansas. Onshore flow across southeast Louisiana and
southern Mississippi could yield 1 to 4 inches as well. A Slight
Risk area was raised for parts of Louisiana, Mississippi and
Arkansas.

Campbell

d
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FOUS30 KWBC 031328
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
928 AM EDT Tue Sep 3 2024

Day 1
Valid 16Z Tue Sep 03 2024 - 12Z Wed Sep 04 2024

....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CENTRAL AND SOUTH TEXAS...

...13Z Outlook Update...

...Texas...
Slight risk areas were combined and expanded to include more of
south Texas (near the Del Rio area). This morning, slow-moving
convection has materialized and produced areas of 1-2.5 inch/hr
rain rates just east of the Rio Grande. These storms are in a
sufficiently moist/unstable enviornment with weak flow aloft for
continued heavy rainfall. Low FFG thresholds (near zero in spots)
were also noted. The flash flood threat should persist for most of
the D1 forecast period under this regime. Reference MPD #0968 for
additional mesoscale details.

...Southeastern Mississippi eastward to northern Florida...
Latest CAMs indicate a robust axis of convection materializing amid
weak flow aloft from the Pine Belt of Mississippi eastward to the
Jacksonville Metro area. HREF probabilities of 24-hr, 3 inch+
precipitation totals maximize near Jacksonville, where models
depict a persistent fetch of deep convection originating along a
frontal boundary over the Gulf Stream. Multiple rounds of
precipitation are expected today through the early overnight
hours especially across northeastern Florida. Localized flash
flood potential is expected where rainfall can occur over
sensitive/urbanized locales. The Marginal risk has been expanded
northwestward and eastward to include areas of isolated flash flood
potential.

The remainder of the forecast is unchanged. Refer to the previous
discussion below for more details.

Cook

...Previous Discussion...

...Texas...

The mid-level vort is expected to exit the region although
precipitable water values will remain high. Flooding issues will be
possible in the area with a widespread 1 to 1.5 inches forecast
with locally higher amounts. A Slight Risk remains in effect for
central portions of the state although it was expanded y 1 tier of
counties to the south to reflect the latest trends in the guidance.
A slow moving tropical low will continue to bring periods of heavy
rain in the form of slow- moving showers and thunderstorms from
the Gulf into the adjacent Texas Coast. Most areas will not see
steady rain the entire time, but very localized areas of training
storms resulting in flash flooding. The heaviest rains in the
state are expected to be along the Gulf Coast from Galveston south
and west through Corpus Christi. Locally heavy rains to 2 inches
per hour will be possible.

...Mississippi and Alabama Gulf Coast...

The Marginal Risk was maintained for the potential of slow moving
and training storms to the east of the low along a stalling front
into coastal Mississippi and Alabama. The abundance of atmospheric
moisture and instability, as well as, the slow-moving nature of
the synoptic systems increases confidence that an isolated flash
flood or two could develop along this stretch of coast.

...Idaho/Montana...

There is potential for isolated to scattered heavy rainfall as an
advancing shortwave encounters an anomalously moist airmass. PW
values rising to near 1 inch will support storms capable of heavy
rain that may produce isolated flash flooding should the storms
impact particularly flood sensitive or more urban areas.

Campbell


Day 2
Valid 12Z Thu Sep 05 2024 - 12Z Fri Sep 06 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE MISSISSIPPI
DELTA REGION AND ADJACENT GULF COAST...

...Gulf Coast and Lower Mississippi Valley...

The surface front will continue to be draped west to east across
the South, albeit further south than previous forecast cycles. This
frontal boundary will provide focus for showers and thunderstorms
to spread across the entire Gulf Coast from south Texas all the
way to the Florida Peninsula on Wednesday. Most of the guidance
shows 1 to 3 inches will concentrate over this part of the region
thus increasing the risk for excessive rainfall and local flooding
potential.

There is the potential for a few locations for local
maximums to exceed 6 inches near northern Louisiana/Arkansas.
Onshore flow across southeast Louisiana and southern Mississippi
could yield 1 to 4 inches as well. The focus for the heaviest rains
will be in the central Gulf Coast from Louisiana east through the
Florida Panhandle. Locally heavy rains are likely, especially from
New Orleans east through Pensacola, where a higher-end Slight is in
place. With increasing amounts of rain forecast in and around New
Orleans, continued increases in rainfall there may require an
eventual targeted Moderate Risk should trends continue.

Given the trends, the back edge of the Marginal Risk was trimmed
eastward toward the Texas coast in addition to reducing the
northern boundary by 1 tier of counties across Alabama and
Mississippi.


Campbell/Wegman


Day 3
Valid 12Z Thu Sep 05 2024 - 12Z Fri Sep 06 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ALONG THE CENTRAL
GULF COAST...

...Gulf Coast and Lower Mississippi Valley...

The area of precipitation mentioned for the Day 2 period will
shift eastward across the central Gulf Coast with the heaviest QPF
still focusing across portions of southeast Louisiana, southern
Alabama, southern Mississippi and clipping western portions of the
Florida panhandle. Again, there was a notable southern shift in
placement within a majority of the guidance from previous
cycles.coastlineThe inherited Marginal Risk areas was removed
from southern Tennessee and northern portions of Alabama,
Mississippi and northwest Georgia while trimmed eastward across
central Louisiana. The Slight Risk spans along the Gulf Coast from
west-central Louisiana to eastern Choctawhatchee Bay Florida.

Campbell
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FOUS30 KWBC 040824
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
424 AM EDT Wed Sep 4 2024

Day 1
Valid 12Z Wed Sep 04 2024 - 12Z Thu Sep 05 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE MISSISSIPPI
DELTA REGION AND ADJACENT GULF COAST...

...Gulf Coast and Lower Mississippi Valley...

The surface front will continue to be draped west to east across
the South provide focus for convection to spread from south Texas
to Florida Peninsula. The latest guidance has continued to favor a
less progressive eastward advancement with the precipitation
shield. A blend of CAMs/global guidance has shifted the focus for
heavier rainfall to be along the Upper Texas coast where they will
be located closest to an organizing and elongated area of low
pressure in the western Gulf of Mexico. General consensus has 2 to
5 inches along the coast between Corpus Christi and Lake Charles. Southeast
TX also still sports >80% soil moisture percentiles within the
0-40cm layer according to NASA SPoRT-LIS, suggesting soils there
would be more sensitive to 2-3"/hr rainfall rates.

Onshore flow across southeast Louisiana and southern Mississippi
could yield 1 to 2 inches as well. Locally heavy rains are likely,
especially from New Orleans east to Mobile. For the Florida
Panhandle there will be an influx of anomalous PWs and modest
instability along the stalled frontal boundary that may trigger
additional thunderstorms capable of producing torrential downpours.
Areas most at risk for possible flash flooding will be areas whose
soils are more saturated following Tuesday's thunderstorm activity
and as far east as the Jacksonville metro area.

Campbell


Day 2
Valid 12Z Thu Sep 05 2024 - 12Z Fri Sep 06 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ALONG THE CENTRAL
GULF COAST...

...Gulf Coast and Lower Mississippi Valley...

The latest guidance keeps a slower progression of the QPF
associated with an elongated area of low pressure in the northwest
Gulf of Mexico. As such, the Slight Risk area was expanded further
west along the Gulf Coast, between Houston and Corpus Christi, to
account for the westward trend. While dispersion is on the higher
side on Day 2, there is a better consensus for heavier rainfall
along the central Gulf Coast given the bulk of PWs >99th
climatological percentile residing along the Gulf Coast. The region
is also closer to the surface-850mb southeasterly flow that will
sustain a steadfast regime of low level theta-e advection into the
nearby stationary frontal boundary. Additional forecast changes are
likely given so much of this setup lies with the development of
low pressure along the Gulf Coast.

...New Mexico and Colorado...

Convection is expected to fire up ahead of an approaching cold
front thanks to PWs topping 0.75" and up to 500 J/kg of MUCAPE.
Soils across this part of the region are sensitive given recent
moisture and burn scars. The Marginal Risk area was maintained for
the localized flash flood potential for the afternoon and evening.

Campbell/Mullinax


Day 3
Valid 12Z Fri Sep 06 2024 - 12Z Sat Sep 07 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CENTRAL AND EASTERN GULF COAST...

...Gulf states and Southeast...

The frontal boundary is expected to slowly progress eastward during
this period will draped along the Gulf Coast and the Southeast.
Deep moisture will continue to override the boundary helping to
concentrate the heaviest QPF along the central and eastern Gulf
coast. A Slight Risk remains in effect from southeast Louisiana to
the Florida Panhandle while a Marginal Risk area spans from south-
central Louisiana to northeast Florida and northward to South
Carolina. Areal averages of 1 to 2 inches will be common across the
region with the possibility of very isolated maxes of 3 to 5
inches, especially along the coastline.

Campbell
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FOUS30 KWBC 050828
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
428 AM EDT Thu Sep 5 2024

Day 1
Valid 01Z Thu Sep 05 2024 - 12Z Thu Sep 05 2024

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL ALONG THE
CENTRAL GULF COAST...

...Gulf Coast, Lower Mississippi Valley and Southeast...

In coordination with local forecast offices near the Mississippi
Delta region, a Moderate Risk area was hoisted for this period to
include portions of southeast Louisiana and southern Mississippi. There
is consensus for heavier rainfall along the central Gulf Coast
given the bulk of PWs >99th climatological percentile residing
along the Gulf Coast. The region is also closer to the
surface-850mb southeasterly flow that will sustain a steadfast
regime of low level theta-e advection into the nearby stationary
frontal boundary. Additionally, the latest guidance shows a
potential for locally higher amounts upwards of 10" per NBM 95th
percentile to focus in the vicinity of the New Orleans metro and
points east and south. A Slight Risk spans from the southeast Texas
coast to southern Mississippi.

Deep-layer instability across portions of the Southeast may be
lacking, however PWs of 2.2-2.4" will make for highly-efficient
rainfall rates as the quasi- stationary front shifts a bit
northward by tonight as the upper shortwave trough dips across the
western Gulf Coast. A Marginal Risk spans from extreme southern
South Carolina to central Florida and westward to the central Texas
coast.

...New Mexico and Colorado...

Convection is expected to fire up ahead of an approaching cold
front thanks to PWs topping 0.75" and up to 500 J/kg of MUCAPE.
Soils across this part of the region are sensitive given recent
moisture and burn scars. The Marginal Risk area was maintained for
the localized flash flood potential for the afternoon and evening.

Campbell/Hurley


Day 2
Valid 12Z Thu Sep 05 2024 - 12Z Fri Sep 06 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL AND EASTERN GULF COAST...

...Gulf states and Southeast...

During this period the trough will be digging across the western
Gulf Coast region and increasing (and persistent) low-level
frontogenesis along the central-eastern Gulf Coast to the Georgia
Coast. While narrowing with time, the corridor of favorable
thermodynamics (PWs of 2.2 to 2.5" with tall/skinny CAPE profile)
and low-level FGEN along the quasi-stationary surface boundary will
favor the more intense short term rainfall rates. This is
essentially where the Slight Risk was drawn, which also correlates
well with the highest 24hr QPF exceedance probabilities from the
NBM.

While there is some spread on exactly where the highest QPF will
focus there is a general consensus for 1 to 3 inches across the
region. Local maxes may be closer to with the possibility of very
isolated maxes of 4 to 7 inches, especially along the coastline.
The NAM, although hedging toward being an outlier solution for
this period, does show isolated maximums closer to 10 inches. At
this time, a Slight Risk seems to adequately cover the level of
threat for excessive rainfall and flooding concerns. There may be
the need to upgrade with a targeted Moderate Risk along the central
Gulf Coast should guidance continue to trended up.

Campbell/Hurley


Day 3
Valid 12Z Fri Sep 06 2024 - 12Z Sat Sep 07 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE EASTERN GULF COAST AND SOUTHEAST ALONG WITH PORTIONS OF THE NORTHEAST...

...Gulf Coast and Southeast...

Slow moving convection will continue to focus along the draped
frontal system along the Gulf Coast and Southeast U.S. Abundant
Gulf moisture will continue to feed into the region leading to
higher rainfall rates. Multi-day rains will have increased soil
saturation and lowered flash flood guidance by this period thus
there will be a continued threat for excessive rainfall and local
flooding concerns. A Marginal Risk is in effect across northern
Florida and southern Georgia.

...Northeast...

An upper trough/low will pivot across the region during this
period sending showers and thunderstorms across the Northeast where
multiple recent rains have increased soil sensitivity. A Marginal
Risk area is in effect for eastern New York, northeast
Pennsylvania, northern New Jersey and northwest Vermont.

Campbell
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FOUS30 KWBC 060804
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Fri Sep 6 2024

Day 1
Valid 12Z Fri Sep 06 2024 - 12Z Sat Sep 07 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR SOUTHEASTERN
LOUISIANA...

...Gulf Coast & Southeast...

A very slow moving tropical low will track east along a stationary
front draped along the Gulf Coast today. Near record amounts of
atmospheric moisture in place across the Gulf will be drawn
northward into the front ahead of the low. PWATs currently are
around 2.6 inches and will not change much through the day. This
would be over 3 sigma above normal for this time of year...which
for southeastern Louisiana is no small feat.

The southerly flow ahead of the low will keep a steady supply of
deep Gulf moisture tracking into the Gulf Coast primarily...but
will spread east across portions of the Southeast in the Slight
Risk. The big question about heavy rain will be how much
instability will be available for any showers and thunderstorms.
Since it's currently raining over much of Louisiana and will
continue into tonight, any instability will need to be advected in
to the Gulf. That said, given the near record levels of moisture
available, it will not take much to result in 2+ inch per hour
rates with the strongest convection. The area's soils are quite
water-logged from multiple days of rains, so today's rainfall
should fully convert to runoff...greatly increasing the flooding
threat.

In coordination with LIX/Slidell, LA forecast office, the Moderate
Risk area was left unchanged with this update, with the greatest
threat for the greater New Orleans and Baton Rouge areas due to
lower FFGs. The Slight was nudged a row of counties north, and
removed from most of northeast Florida. Due to recent heavy rains
across much of the Peninsula however, the Marginal risk was
expanded to include the Orlando, Tampa, and Ft. Myers metros.

...New Mexico...

A small low-confidence Marginal Risk area was added for the
Sacramento Mountains of south-central New Mexico with this update.
Afternoon showers and thunderstorms may form right over the very
flood prone burn scars near Ruidoso, which could cause local flash
flooding once again. However, it would require just that scenario
to unfold for flooding to occur which is low confidence since the
storm would have to form right over the correct spot, a microscale
challenge that's nearly impossible to know for sure well in
advance. The pattern supports one more day of area showers and
storms, prompting the localized upgrade.

Wegman


Day 2
Valid 12Z Sat Sep 07 2024 - 12Z Sun Sep 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
EMERALD COAST OF THE FLORIDA PANHANDLE...

...Southeast...

The stationary front from Friday will drift southeastward across
the Southeast on Saturday. For the Central Gulf Coast, it would
probably be more accurate to call it a cold front, as the front
will make steady progress across southern Louisiana and into the
northwestern Gulf. Meanwhile across the Southeast, the front will
stall out over the Florida Panhandle, southern Georgia and up the
Carolina coast. It's in this region where training storms may cause
localized flash flooding. Moisture will not be a problem at all as
PWATs will be from 2 inches in the Carolinas to nearly 2.5 inches
in the Florida Panhandle. Thus, just as on Friday, the big limiting
factor for heavy rainfall will be instability, as very slow moving
fronts tend to be very lacking in that department due to extensive
cloud cover.

In coordination with TAE/Tallahassee, FL forecast office, a Slight
Risk area was introduced with this update. Storms are likely to be
robust rain makers out over the northern Gulf on Saturday. With
very weak steering flow and limited instability inland however,
the area with greatest likelihood for the storms to impact land
will be around the Emerald Coast of the Florida Panhandle. The most
likely hazard area was highlighted in the Slight. The expectation
is that any storms that move into the Emerald Coast will greatly
struggle to maintain the heavy rainfall rates more than a few miles
inland from the coast, so the Slight is only for the immediate
coast.

The Marginal Risk area was expanded several rows of counties north
with this update, while in the Carolinas it was more like a couple
states. The primary driving factor for these changes is the slowing
of the front in recent model runs. Thus, the rain may persist for a
bit longer than expected into Saturday morning on the northern edge
of the Marginal Risk area. Meanwhile Saturday will be another day
with potential strong thunderstorms capable of heavy rains across
the northern Florida Peninsula. This hard-hit area is likely to see
multiple days of afternoon thunderstorms capable of isolated flash
flooding.

...Northeast...

The inherited Marginal Risk area was removed in coordination with BTV/Burlington, VT and ALY/Albany, NY forecast offices. Fast-moving
storms with this fast-moving front in this part of the country,
very limited/no instability, and somewhat dry weather in recent
days should all preclude any flash flooding in this area.

Wegman


Day 3
Valid 12Z Sun Sep 08 2024 - 12Z Mon Sep 09 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE GULF COAST...

...Louisiana to the Atlantic Coast...

The stalled out front will weaken in place through the day on
Sunday. This once again should prevent most areas from getting
prodigious amounts of rain, despite abundant atmospheric moisture.
Further, there is increasing disagreement in the guidance as to
where the axis of heaviest rainfall associated with the front will
be on Sunday. Guidance trends have been towards the northwest,
resulting in a large expansion of the Marginal in that direction
due to the aforementioned uncertainty. It's likely given how wet
this entire area of the country has been that an area of Slight
Risk impacts will occur somewhere within the Marginal risk, but
where that will be is highly uncertain right now. Thus, it's likely
a Slight Risk upgrade will be needed with increased confidence.

...Deep South Texas...

A Marginal Risk area was added to the Brownsville to South Padre
Island area of Deep South Texas with this update. A tropical wave
will have moved through the Caribbean and into the western Gulf by
Sunday. Associated heavy rainfall may impact the immediate Deep
South Texas coast. Recent heavy rainfall has lowered FFGs here
which may not fully recover by the arrival of this heavy rainfall
due to potential additional shower and thunderstorm activity both
today and Saturday prior to this period.

Wegman
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FOUS30 KWBC 080817
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
417 AM EDT Sun Sep 8 2024

Day 1
Valid 12Z Sun Sep 08 2024 - 12Z Mon Sep 09 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST, DEEP SOUTH TEXAS, AND SOUTHEAST...

...Summary...

Only a few very minor changes were made to the inherited Marginal
Risk areas across the CONUS.

...Southwest...

A bit more widespread convection is expected with the monsoon this
afternoon across the Southwest. Much of the convection will once
again be focused along the various mountain ranges from the
Peninsular Ranges of southern California through the Sangre de
Cristos of Colorado. As usual in the desert Southwest, somewhat
limited moisture will be the limiting factor, even though areas
could be 2 sigma above normal for atmospheric moisture for this
time of year. Thus, the primary flood threat is for urban areas,
slot canyons, and arroyos where slow moving convection in chaotic
steering flow may result in long-duration localized heavy rain from
the most persistent convection. Any resultant flash flooding will
be isolated.

...Deep South Texas...

The Marginal Risk area was trimmed closer to the coast with this
update, now primarily for the urban area of Brownsville over to the
South Padre Island beaches. A stalled out front will begin to focus
an area of heavy rainfall associated with a slowly developing
tropical low over the western Gulf. Guidance has shifted east a
bit, resulting in lower forecasted rainfall totals for all of Deep
South Texas, with little if any rain expected west of Brownsville
through tonight. However...given the abundance of atmospheric
moisture available any stronger showers and storms will be capable
of very heavy rainfall rates which could cause isolated flash
flooding.

...Southeast...

The stalled out front that has been haunting the Southeast for well
over a week now remains in place from far southern South Carolina
through the northern Florida Peninsula. Besides the front itself
being strong...indicative of a tight gradient between the extremely
humid air mass over the Gulf and an outright autumnal air mass to
its north...instability remains very lacking since this front
hasn't moved in days, so diurnal heating is limited under the
extensive low cloud cover. Thus, almost all of the rain will be
light across this region. This is countered by the aforementioned
abundant amounts of atmospheric moisture available for any
convection that can form. Thus, a low-end Marginal remains in
place, with the greatest threat for flooding over the Florida
Peninsula well south of the front where diurnal heating can
actually make a difference.

Wegman


Day 2
Valid 12Z Mon Sep 09 2024 - 12Z Tue Sep 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR COASTAL DEEP
SOUTH TEXAS...

As on Day 1, very few changes were needed to the inherited ERO risk
areas.

...Coastal Deep South Texas...

Weak easterly flow north of a developing tropical low over the
southwestern Gulf will advect increasingly deep tropical moisture
into coastal Deep South Texas on Monday. This is highly likely to
result in much more rainfall for South Padre Island and over to
Brownsville as compared with Day 1/Sunday. Given PWATs that could
exceed 2.5 inches, or 3 sigma above normal for this time of year,
any convection that moves west off the Gulf into the coast will be
capable of very heavy rain rates. Thus, the real question regarding
flood coverage will be how frequent storms producing those rates
move over urban areas. Think right along the coast widely scattered
instances of flash flooding can be reasonably expected. Any
training could quickly result in significant flash flooding. That
said, the system will only really just be getting organized, so
overall rains will likely be more intermittent in most areas. Urban
areas such as Brownsville will be at a higher likelihood for flash
flooding.

...Four Corners Region...

Convective coverage should shift northeastward a bit on Monday.
Thus, the flooding threat shifts into the Four Corners region and
away from the West Coast. Flooding concerns will be greatly
focused in area slot canyons and arroyos of southern Utah and
southwest Colorado Monday afternoon and evening with peak heating.

...Rest of the Gulf Coast...

Rinse and repeat weather pattern will continue, albeit shifted just
a bit south of Sunday's focus. Thus, most of the north Gulf Coast
will get a relative break from the potential for steady heavy rain,
as the heaviest rains shift south a bit away from the coast. The
exception will be into the Florida Peninsula, where a repeat day of
sea breeze showers and thunderstorms can be expected to the south,
with more widespread lighter rain expected further north.

Wegman
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FOUS30 KWBC 081545
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1145 AM EDT Sun Sep 8 2024

Day 1
Valid 16Z Sun Sep 08 2024 - 12Z Mon Sep 09 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST, DEEP SOUTH TEXAS, AND SOUTHEAST...

...16Z Update...

Very little changes were made to the overall D1 outlook with the
consensus remaining steady for low to medium end MRGL impacts
expected across portions of the West, Southeast, and Deep South
Texas. A small shift was made across South TX where the MRGL risk
was tightened even further to the coast to confine mainly
Brownsville and South Padre Island as the two main areas of focus
with the northern periphery of any banding associated with the
tropical wave to the south. The latest 12z HREF mean QPF output
depicts a sharp western gradient for precip through the period with
the best potential aligning with the overnight time frame as the
wave scoots more to the northwest, bringing some of the deeper
tropical moisture north into the tip of South TX. There's some
discrepancy on the timing of any banding with a 50/50 split amongst
CAMs and some global deterministic. There's enough merit to
warrant the continued MRGL to maintain continuity, especially with
a tropical disturbance positioned to the south. There's a chance
this materializes after the period, but as a precaution for the
low-end threat, decided against removal.

Over the Southeast, the main focus will reside along the coasts of
FL and perhaps over the coast of SC as convection will align near
the coastline during peak diurnal destabilization. The best
opportunity for heavy rain will likely occur with the sea breeze
across Northeast FL between Jacksonville to Melbourne with the HREF neighborhood probabilities and EAS both fairly aggressive in the
latest update for >3" of rainfall in the vicinity. The airmass in
place is sufficient for these higher hourly and intra-hour rates to
produce some localized flash flood concerns, especially within the
urbanized areas along the coast. This was enough maintain the MRGL
risk with no real changes to the risk positioning from previous
forecast.

Out West, the only change occurred over the northern extent of the
Peninsular range where 12z CAMs indicate a few cells developing
just north of where the risk area was forecast. HREF mean SBCAPE
values lie within the 500-1000 J/kg with a few CAMs a bit more
robust in the depiction. Considering a marginally more favorable
airmass overhead and the complex terrain additions over the area,
thought the expansion was favorable and was agreed upon in
coordination with the San Diego WFO. Otherwise, no other changes
were necessary from the previous issuance across the west.

Kleebauer

..Previous Discussions..

...Southwest...

A bit more widespread convection is expected with the monsoon this
afternoon across the Southwest. Much of the convection will once
again be focused along the various mountain ranges from the
Peninsular Ranges of southern California through the Sangre de
Cristos of Colorado. As usual in the desert Southwest, somewhat
limited moisture will be the limiting factor, even though areas
could be 2 sigma above normal for atmospheric moisture for this
time of year. Thus, the primary flood threat is for urban areas,
slot canyons, and arroyos where slow moving convection in chaotic
steering flow may result in long-duration localized heavy rain from
the most persistent convection. Any resultant flash flooding will
be isolated.

...Deep South Texas...

The Marginal Risk area was trimmed closer to the coast with this
update, now primarily for the urban area of Brownsville over to the
South Padre Island beaches. A stalled out front will begin to focus
an area of heavy rainfall associated with a slowly developing
tropical low over the western Gulf. Guidance has shifted east a
bit, resulting in lower forecasted rainfall totals for all of Deep
South Texas, with little if any rain expected west of Brownsville
through tonight. However...given the abundance of atmospheric
moisture available any stronger showers and storms will be capable
of very heavy rainfall rates which could cause isolated flash
flooding.

...Southeast...

The stalled out front that has been haunting the Southeast for well
over a week now remains in place from far southern South Carolina
through the northern Florida Peninsula. Besides the front itself
being strong...indicative of a tight gradient between the extremely
humid air mass over the Gulf and an outright autumnal air mass to
its north...instability remains very lacking since this front
hasn't moved in days, so diurnal heating is limited under the
extensive low cloud cover. Thus, almost all of the rain will be
light across this region. This is countered by the aforementioned
abundant amounts of atmospheric moisture available for any
convection that can form. Thus, a low-end Marginal remains in
place, with the greatest threat for flooding over the Florida
Peninsula well south of the front where diurnal heating can
actually make a difference.

Wegman


Day 2
Valid 12Z Mon Sep 09 2024 - 12Z Tue Sep 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR COASTAL DEEP
SOUTH TEXAS...

As on Day 1, very few changes were needed to the inherited ERO risk
areas.

...Coastal Deep South Texas...

Weak easterly flow north of a developing tropical low over the
southwestern Gulf will advect increasingly deep tropical moisture
into coastal Deep South Texas on Monday. This is highly likely to
result in much more rainfall for South Padre Island and over to
Brownsville as compared with Day 1/Sunday. Given PWATs that could
exceed 2.5 inches, or 3 sigma above normal for this time of year,
any convection that moves west off the Gulf into the coast will be
capable of very heavy rain rates. Thus, the real question regarding
flood coverage will be how frequent storms producing those rates
move over urban areas. Think right along the coast widely scattered
instances of flash flooding can be reasonably expected. Any
training could quickly result in significant flash flooding. That
said, the system will only really just be getting organized, so
overall rains will likely be more intermittent in most areas. Urban
areas such as Brownsville will be at a higher likelihood for flash
flooding.

...Four Corners Region...

Convective coverage should shift northeastward a bit on Monday.
Thus, the flooding threat shifts into the Four Corners region and
away from the West Coast. Flooding concerns will be greatly
focused in area slot canyons and arroyos of southern Utah and
southwest Colorado Monday afternoon and evening with peak heating.

...Rest of the Gulf Coast...

Rinse and repeat weather pattern will continue, albeit shifted just
a bit south of Sunday's focus. Thus, most of the north Gulf Coast
will get a relative break from the potential for steady heavy rain,
as the heaviest rains shift south a bit away from the coast. The
exception will be into the Florida Peninsula, where a repeat day of
sea breeze showers and thunderstorms can be expected to the south,
with more widespread lighter rain expected further north.

Wegman
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FOUS30 KWBC 090830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
430 AM EDT Mon Sep 9 2024

Day 1
Valid 12Z Mon Sep 09 2024 - 12Z Tue Sep 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR COASTAL DEEP
SOUTH TEXAS...

...Coastal Deep South Texas...

The Slight Risk for the coastal sections of Cameron, Willacy, and
southeast Kenedy Counties remains largely unchanged, though trimmed
a hair on the west/inland side with this morning's forecast update.
The northern edge of the convection associated with Potential
Tropical Cyclone Six (hereafter, PTC6), will try to move into the
coast today into tonight. A strong front remains draped over South
Texas, along the coast, but extending west/inland over Deep South
Texas. This front is keeping dry air nearby, greatly limiting any
westward extent to the rainfall, but is also a source of forcing
for the very deep tropical moisture currently in place over most of
the Gulf. Thus, as PTC6 organizes today into tonight, waves of rain
may move into the coast over South Padre Island and Brownsville.
Widely scattered instances of flash flooding are probable,
especially where the storms are the most persistent today.

...Louisiana through Florida Gulf Coast...

Few changes were made to the Marginal Risk area...which will be
largely in place for afternoon sea breeze convection as deep
tropical moisture associated with PTC6 move east across the
Peninsula and along the Gulf Coast. There has been a nominal
southward shift in the guidance, so the Marginal was trimmed to
just the immediate Gulf Coast except over the Florida Peninsula
where sea breezes and outflow boundaries will be much more of a
factor in forcing storms capable of producing heavy rain and
resultant flash flooding.

...Four Corners...

No changes were made to the Marginal Risk area, where isolated
flash flooding is possible especially in slot canyons and arroyos.
Guidance has backed off a bit on the areal coverage of convection
in this region, so this area is a low-end Marginal.

Wegman


Day 2
Valid 12Z Tue Sep 10 2024 - 12Z Wed Sep 11 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR ALL OF THE GULF
COAST WEST OF PENSACOLA..

...Gulf Coast...

Potential Tropical Cyclone 6 (PTC6) will continue organizing over
the western Gulf based on the latest NHC forecast as it tracks
north and east over the northwestern Gulf. Heavy rains associated
therewith will impact all of the Gulf Coast, especially into
Louisiana and Texas. The latest guidance has been shifting the
axis of heaviest rainfall east, in response to very dry air north
of a strong front that will be guiding PTC6 northeastward. Thus,
the westward extent of the associated rainfall will be greatly
limited. Thus, the inherited Slight Risk was trimmed from the west,
especially over Texas. With that said, any heavy rain associated
with PTC6 will have well above average amounts of atmospheric
moisture to work with, making it more common for prodigious
rainfall rates to occur. Much of southern Louisiana has been very
wet in recent weeks, so saturated soils will only quicken the onset
of flooding once the heavy rain gets going.

Into Florida, the same stalled out front will shear some of the
moisture from PTC6's circulation, adding fuel for diurnally driven
showers and storms once again on Tuesday afternoon. Isolated flash
flooding will be possible once again.

...Utah/Colorado...

No changes were made to the inherited Marginal Risk area, where
numerous showers and storms may develop Tuesday afternoon. The most concentrated and heaviest showers and storms will be in the
Marginal Risk area from eastern Utah into western Colorado.
Isolated flash flooding will be possible in flood prone areas such
as slot canyons.

Wegman


Day 3
Valid 12Z Wed Sep 11 2024 - 12Z Thu Sep 12 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE
MISSISSIPPI DELTA...

Potential Tropical Cyclone Six (PTC6) is forecast to continue
strengthening up until landfall in southwest Louisiana on
Wednesday. Abundant associated moisture will advect north ahead of
and alongside the low center, resulting in multiple inches of rain
over almost all of Louisiana and adjacent southern Mississippi. For
Louisiana, much of the southern half of the state has seen abundant
rainfall over the past couple weeks, resulting in highly saturated
soils. A hurricane making landfall here will cause most of the rain
to convert to runoff. Thus, in coordination with LCH/Lake Charles,
LA; LIX/Slidell, LA; JAN/Jackson, MS, and SHV/Shreveport, LA
forecast offices, a Moderate Risk upgrade was introduced with this
update. The greatest risk of significant and potentially life-
threatening flash flooding will be in the hardest hit areas of the
I-10 corridor from New Orleans west through Baton Rouge to
Lafayette. A higher-end Moderate is considered in effect for this
portion of the I-10 corridor.

Considerable uncertainty persists on the north and west side of the
ERO risk areas. To the west, a notable and persistent drying trend
continues, partially due to eastward shifts in the track and
partially due to disagreement as to whether PTC6 will begin
extratropical transition around landfall. With the center expected
to track along the spine of Louisiana, locations to the west will
be on the dry side of the storm, which will quickly cut down on
rainfall totals. Given these trends, the Slight was trimmed on the
western side. To the north, the concern will be more about rapidly deteriorating antecedent conditions, as northern Louisiana,
Mississippi, and Arkansas have all been much drier than points
further south towards the Gulf Coast. This in turn will make the
watersheds much more able to absorb heavy rainfall before
significant flooding commences. Thus, the Slight and Marginal Risk
areas are quite conservative, as the first few inches of rain
should be largely beneficial in these areas.

The aforementioned eastward shift in track should mean wetter
conditions into Alabama and the Florida Panhandle, and the Slight
was expanded east for that reason, though Alabama has been
similarly dry away from the Gulf Coast as its neighbors to the
west.

With PTC6 really still trying to form, expect continued adjustments
in the track and expected rainfall associated therewith.
Uncertainty with locations and amounts have also precluded some
areas well away from the current forecast track of the center from
being upgraded, but may be with future updates, especially east of
the track.

...Intermountain West...

A Marginal Risk was introduced for this region as a strong digging
shortwave trough interacts with topography and above normal
moisture for this region. Forecast amounts may be high enough to
potentially need a targeted Slight with future updates in this
area.

Wegman
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FOUS30 KWBC 100727
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
327 AM EDT Tue Sep 10 2024

Day 1
Valid 12Z Tue Sep 10 2024 - 12Z Wed Sep 11 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL GULF COAST...

...Gulf Coast...
Tropical Storm Francine will continue making headway to the north
and northeast towards Louisiana, with NHC forecasting the system to
become a hurricane. The combination of dry/cool air to the west
and northwest of the storm will lead to a tight rainfall gradient
on its west side. Further enhancing the western gradient will be
the increasing vertical wind shear with time out of the west-
southwest, which will attempt to shift convection downshear and
downshear left of its center (to its northeast). With QPF
continuing to trend downward, the Slight Risk for the TX coast was
removed this cycle. Across the immediate Brownsville and Port
Isabel area, recent heavy rains could make them more sensitive to
additional rainfall this morning. Even though the risk area was
reduced to Marginal, Slight Risk impacts cannot be ruled out.

Prospects increase gradually along the central Gulf Coast for
heavy rainfall. While initial bands from the periphery of tropical
cyclones can quickly erode existing instability ashore, portions of
Acadiana and Southeast Louisiana along with far southern MS have
had an exceeding wet week from a cyclone that ultimately merged in
with Francine, so keeping the inherited Slight Risk makes sense.
Also, guidance tends to bias slow with tropical cyclone
recurvature, and this Slight Risk area can account for some
possible track acceleration between now and its coastal approach.
As with any warm core cyclone, the low-level inflow will exceed
the mean flow, aiding precipitation efficiency. Plentiful effective
bulk shear will organize convection into curved bands within its
cyclonic circulation. Hourly rain totals to 3" will be possible
with any bands that manage to train.

...Florida...
An unusually far south synoptic front for Mid-September focuses
very high moisture east of Francine where, at times, effective bulk
shear could flirt with 25 kts. Where semi- organized and organized
convection manages to form, hourly rain totals to 3" and local
amounts to 6" are considered possible where storms merge, train, or
get tied to the boundary. The 00z NAM and 00z Canadian were
especially bullish with local maxima, both remained widely
scattered to isolated in coverage of the heaviest rainfall. This
kept the risk at the Marginal level.

Another area with sufficient instability and moisture is behind
the front near the northeast FL coast. Adding to possible issues
there is low level and upper level flow trying to zero out. Short
bands of efficient convection, which could lead to hourly totals to
2" and local amounts to 4", are possible. Kept this area in the
Marginal Risk to help support their flood watch.

...Inter-Mountain West and Southern Rockies...
A scattered convective footprint is anticipated across portions of
the West with the main threat residing over the Southern Rockies
into the Wasatch of UT. The threat is on the lower end of
probabilities considering the middling signal within the latest
HREF for >1" chances over the region. However, with precipitable
water values near 0.75" and sufficient instability, localized flash
flooding can't be ruled out in any dry washes/arroyos, burn scars,
slot canyons, or steep topography where hourly rain totals manage
to reach 1.5". The Marginal Risk area maintained showed good
continuity.

Roth


Day 2
Valid 12Z Wed Sep 11 2024 - 12Z Thu Sep 12 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
LOUISIANA AND SOUTHERN MISSISSIPPI...

...Southeast...
Francine should begin extratropical transition and become highly
sheared around, if not before, the time of landfall Wednesday afternoon/evening, with a developing dry slot possible. This should
lead to a convective comma head and an inflow band/baroclinic
trough/developing front becoming increasing removed to the east of
its center which would both be foci for heavy/excessive rainfall.
The cities of Lafayette, Baton Rouge, and New Orleans (along with
their suburbs) would be most susceptible for flash flooding as
hourly rain totals to 4" (if not more) should be possible,
particularly within the trailing band/forming front to its
southeast. Acadiana and Southeast Louisiana are more susceptible
due to heavy rainfall from this past week caused by the cyclone
which merged in with Francine, so the soils will be more primed
relative to what is typical to the area. Continuity was generally
maintained in the risk areas.

...Intermountain West...
A deep layer cyclone moving into MT brings moderate to strong
upslope flow into western portions of the state, along with MU CAPE
of ~750 J/kg. Precipitable water values are sufficient for heavy
rain-related issues, so increased the risk area to Slight for
portions of western MT. Hourly rain totals to 1.5" with local
amounts to 3" are expected, which would be most impactful in burn
scars. Some of the QPF would be in the form of snow at the highest
elevations of the northern Continental Divide.

Roth


Day 3
Valid 12Z Thu Sep 12 2024 - 12Z Fri Sep 13 2024

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR THE MID-SOUTH...

Mid-South/Southeast...
Francine is expected to be fully extratropical, with a well-
developed comma head and trailing front. Guidance suggests that MU
CAPE will be modest, 250-500 J/kg. Effective bulk shear should
continue to be sufficient for convective organization where enough
instability develops/exists. Precipitable water values remain
near 2", so hourly rain totals up to 1-2" should be possible, which
would be most problematic in urban areas and initially beneficial
elsewhere. This region has been quite dry lately. With the volume
of rain expected, and the concept of this being on the cusp of a
flash flood and longer duration flood event, kept the Slight Risk
area which showed minimal change from continuity. Across the
Southeast, there is a risk of training convection along Francine's
cold front, but its progression is expected to limit issues. Still,
hourly rain totals to 2" and local amounts to 4" should be
possible.

Western MT, Idaho Stovepipe & Vicinity...
One or two surface lows are expected to lift northward this
period through MT, drawing in sufficient upslope flow, moisture,
and instability from the east to be concerned about the potential
for organized convection. The guidance signal is not cohesive as of
yet, so left the risk across the area as Marginal. Should the
guidance get more agreeable or confidence increase, a Slight Risk
could become necessary in later updates. Hourly rain totals to 2"
and local amounts to 4" appear possible.

Roth
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FOUS30 KWBC 102042
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
442 PM EDT Tue Sep 10 2024

Day 1
Valid 16Z Tue Sep 10 2024 - 12Z Wed Sep 11 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL GULF COAST...

...16Z Update...

...Central Gulf Coast and Florida...

Rainfall along the far south Texas Gulf coast should come to an
end by early afternoon, with the expectation that the risk for any
additional heavier rainfall should remain along the immediate
central and upper Texas Gulf Coast as Francine tracks to the north-
northeast. The greater threat will be with bands of convection
already focused along the central Gulf coast far to the northeast
of Francine, with additional bands expected later this evening and
overnight as the center of the system approaches from the
southwest. Updated 12Z hi-res guidance shows remarkably good
agreement on the heaviest rainfall footprint along the central Gulf
Coast, stretching from near Cameron, LA east through southeastern
LA and to the immediate coast of MS. Areal average totals through
early tomorrow morning are on the order of 2-3" with locally higher
amounts of 3-6" possible with training bands.

Additional storms are expected further east in vicinity of a
quasi-stationary frontal boundary draped through central Florida.
Enhanced moisture in the area from Francine will help contribute to
some locally heavy downpours with rain rates of 2-3" per hour,
which could lead to some isolated flooding/ponding issues in urban
areas.

...Intermountain West...

General footprint for the current Marginal Risk remains the same
with a small northwestward extension into southwestern Wyoming to
cover additional areas of scattered convection expected this
afternoon. Latest hi-res guidance indicates the potential for some
locally heavy storm total rainfall of 0.5-1", possibly as high as
1.5", as well as some low-end HREF probabilities (20-30%) of
exceeding 2-year ARIs. These totals may be enough to lead to some
isolated concerns for flash flooding in the usual more terrain
sensitive areas such as slot canyons, dry washes, and any burn
scars.

Putnam

...Previous Discussion...

...Gulf Coast...
Tropical Storm Francine will continue making headway to the north
and northeast towards Louisiana, with NHC forecasting the system to
become a hurricane. The combination of dry/cool air to the west
and northwest of the storm will lead to a tight rainfall gradient
on its west side. Further enhancing the western gradient will be
the increasing vertical wind shear with time out of the west-
southwest, which will attempt to shift convection downshear and
downshear left of its center (to its northeast). With QPF
continuing to trend downward, the Slight Risk for the TX coast was
removed this cycle. Across the immediate Brownsville and Port
Isabel area, recent heavy rains could make them more sensitive to
additional rainfall this morning. Even though the risk area was
reduced to Marginal, Slight Risk impacts cannot be ruled out.

Prospects increase gradually along the central Gulf Coast for
heavy rainfall. While initial bands from the periphery of tropical
cyclones can quickly erode existing instability ashore, portions of
Acadiana and Southeast Louisiana along with far southern MS have
had an exceeding wet week from a cyclone that ultimately merged in
with Francine, so keeping the inherited Slight Risk makes sense.
Also, guidance tends to bias slow with tropical cyclone
recurvature, and this Slight Risk area can account for some
possible track acceleration between now and its coastal approach.
As with any warm core cyclone, the low-level inflow will exceed
the mean flow, aiding precipitation efficiency. Plentiful effective
bulk shear will organize convection into curved bands within its
cyclonic circulation. Hourly rain totals to 3" will be possible
with any bands that manage to train.

...Florida...
An unusually far south synoptic front for Mid-September focuses
very high moisture east of Francine where, at times, effective bulk
shear could flirt with 25 kts. Where semi- organized and organized
convection manages to form, hourly rain totals to 3" and local
amounts to 6" are considered possible where storms merge, train, or
get tied to the boundary. The 00z NAM and 00z Canadian were
especially bullish with local maxima, both remained widely
scattered to isolated in coverage of the heaviest rainfall. This
kept the risk at the Marginal level.

Another area with sufficient instability and moisture is behind
the front near the northeast FL coast. Adding to possible issues
there is low level and upper level flow trying to zero out. Short
bands of efficient convection, which could lead to hourly totals to
2" and local amounts to 4", are possible. Kept this area in the
Marginal Risk to help support their flood watch.

...Inter-Mountain West and Southern Rockies...
A scattered convective footprint is anticipated across portions of
the West with the main threat residing over the Southern Rockies
into the Wasatch of UT. The threat is on the lower end of
probabilities considering the middling signal within the latest
HREF for >1" chances over the region. However, with precipitable
water values near 0.75" and sufficient instability, localized flash
flooding can't be ruled out in any dry washes/arroyos, burn scars,
slot canyons, or steep topography where hourly rain totals manage
to reach 1.5". The Marginal Risk area maintained showed good
continuity.

Roth


Day 2
Valid 12Z Wed Sep 11 2024 - 12Z Thu Sep 12 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
LOUISIANA AND SOUTHERN MISSISSIPPI...

...2030Z Update...

...Southeast...

Minimal adjustments were made to the current Moderate Risk area
focused mainly on a narrowing corridor of heavier rain totals along
and to the east of the forecast path of Francine, which has been
extended a bit further northeastward into Mississippi. This region
covers an area with moderate to high (50-90%) probabilities of
rainfall totals exceeding 5" and rain rates in excess of 2-3" per
hour. The majority of this rainfall is expected to fall within 6-12
hours, exacerbating the potential for scattered to numerous
instances of flash and urban flooding. Storm total rainfall in the
broader Slight Risk area is expected to be on the order of 2-4".
The western edge of the Slight Risk has been trimmed eastward as
increasing shear will limit convection and subsequent rainfall
along the western side of the system track.

...Intermountain West...

Still expect post-frontal, moist upslope flow (PWs 1.0-2.0
standard deviations above the mean) will lead to periods of locally
heavy rainfall across portions of western Montana into central
Idaho. Newly available hi-res guidance shows storm total rainfall
of 1-3", backed by HREF guidance indicating high (70-90%)
probabilities of totals over 1".

Putnam

...Previous Discussion...

...Southeast...
Francine should begin extratropical transition and become highly
sheared around, if not before, the time of landfall Wednesday afternoon/evening, with a developing dry slot possible. This should
lead to a convective comma head and an inflow band/baroclinic
trough/developing front becoming increasing removed to the east of
its center which would both be foci for heavy/excessive rainfall.
The cities of Lafayette, Baton Rouge, and New Orleans (along with
their suburbs) would be most susceptible for flash flooding as
hourly rain totals to 4" (if not more) should be possible,
particularly within the trailing band/forming front to its
southeast. Acadiana and Southeast Louisiana are more susceptible
due to heavy rainfall from this past week caused by the cyclone
which merged in with Francine, so the soils will be more primed
relative to what is typical to the area. Continuity was generally
maintained in the risk areas.

...Intermountain West...
A deep layer cyclone moving into MT brings moderate to strong
upslope flow into western portions of the state, along with MU CAPE
of ~750 J/kg. Precipitable water values are sufficient for heavy
rain-related issues, so increased the risk area to Slight for
portions of western MT. Hourly rain totals to 1.5" with local
amounts to 3" are expected, which would be most impactful in burn
scars. Some of the QPF would be in the form of snow at the highest
elevations of the northern Continental Divide.

Roth
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FOUS30 KWBC 111603
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1203 PM EDT Wed Sep 11 2024

Day 1
Valid 16Z Wed Sep 11 2024 - 12Z Thu Sep 12 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
LOUISIANA AND SOUTHERN MISSISSIPPI...

...16Z update...

The latest NHC track is very similar to the previous issuance
therefore no significant adjustments were needed for the Moderate
and Slight Risk areas that follow the core path of Francine as it
approaches the coast, makes landfall and then moves inland. The
latest guidance did show a decrease in QPF across portions of
eastern Texas and Oklahoma therefore the Marginal Risk area was
trimmed eastward by 1-2 tiers of counties to reflect the reduction
in threat for excessive rainfall.

The latest hi-res and global guidance continues to show convective
activity firing up along the higher terrain areas of western
Montana and central Idaho, with the potential for hourly rainfall
rates to pulse up to 1.5 inches/hour. The inherited Slight Risk
area encompasses where the majority of the guidance suggest an
elevated threat for excessive rainfall and isolated to scattered
instances of flash flooding concerns

Campbell

...Southeast...

Francine should begin extratropical transition and become highly
sheared around, if not before, the time of landfall late on
Wednesday, with a developing dry slot possible. This should cause
sheared convection initially expected to prefer the north and
northeast quadrants -- near and left of track -- and eventually a
convective comma head and an inflow band/baroclinic trough/
developing front becoming increasing removed to the east of its
center which would be foci for heavy/excessive rainfall. The
cities of Baton Rouge and New Orleans (along with their suburbs)
would be most susceptible for flash flooding as hourly rain totals
to 4" (if not more) should be possible, particularly within the
trailing band/forming front to its southeast. Southern Louisiana is
more susceptible due to heavy rainfall from this past week caused
by the cyclone which merged in with Francine, so the soils will be
more primed relative to what is typical to the area. Continuity was
generally maintained in the risk areas, though gradients were
sharpened across LA and the slower track for Francine inland caused
some retreat of the northern fringes of the risk areas.

...Intermountain West...

A deep layer cyclone moving into MT brings moderate to strong
upslope flow into western portions of the state, along with MU CAPE
of ~750 J/kg. Precipitable water values are sufficient for heavy
rain-related issues, so the Slight Risk area remains for portions
of western MT. Hourly rainfall rates up to 1.5 inches/hour will be
possible as individual cells pass through along with a daily
accumulations up to 3 inches in isolated locations; which would be
most impactful in the vicinity of burn scars. Some of the QPF
would be in the form of snow at the highest elevations of the
northern Continental Divide.

Roth/Campbell


Day 2
Valid 12Z Thu Sep 12 2024 - 12Z Fri Sep 13 2024

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
MID-SOUTH & SOUTHEAST...

...Mid-South/Southeast...

Francine is expected to be fully extratropical, with a well-
developed comma head and trailing front. Guidance suggests that MU
CAPE will be modest, 250-500 J/kg. Effective bulk shear should
continue to be sufficient for convective organization where enough
instability develops/exists. Precipitable water values remain
near 2", so hourly rain totals up to 1-2" should be possible, which
would be most problematic in urban areas and initially beneficial
elsewhere. This region has been quite dry lately. With the volume
of rain expected, and the concept of this being on the cusp of a
flash flood and longer duration flood event, kept the Slight Risk
area which showed minimal change from continuity. Across the
Southeast, there is a risk of training convection along Francine's
cold front which shows a greater signal for excessive rainfall
overnight. Broadened the risk area to encompass the possible
training rain band, as enough moisture, instability, and possible
stalling to be concerned about hourly rain totals to 3".

...Western MT, Idaho Stovepipe & Vicinity...

One or two surface lows are expected to lift northward this period
through MT, drawing in sufficient upslope flow, moisture, and
instability from the east to be concerned about the potential for
organized convection. The Slight Risk raised by continuity has been
maintained across portions of western MT. Hourly rainfall rates may
intensify up to 2 inches/hour during this period, with a few
isolated locations possibly accumulating up to 4 inches by the end
of the day.

Roth/Campbell


Day 3
Valid 12Z Fri Sep 13 2024 - 12Z Sat Sep 14 2024

...A MARGINAL RISK OF EXCESSIVE RAINFALL EXISTS ACROSS PORTIONS OF
THE MID-SOUTH AND SOUTHEAST...

A broad Marginal Risk of excessive rainfall exists for portions of
the Mid-South and Southeast with the weakening extratropical/Post-
Tropical Cyclone Francine. The guidance isn't showing a great deal
of overlap in potential heavy rain areas, so left the risk area
as-in, but in theory, portions of northern FL and the Southeast,
possibly including the southernmost Appalachians, have potential
for hourly rain totals to 2.5" and local amounts of 5" as enough
instability and low- level inflow/effective bulk shear exists for
possible issues. Should the guidance align on this idea QPF-wise
further, a Slight Risk could be added in later cycles.

Roth
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FOUS30 KWBC 120053
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
853 PM EDT Wed Sep 11 2024

Day 1
Valid 01Z Thu Sep 12 2024 - 12Z Thu Sep 12 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
LOUISIANA AND SOUTHERN MISSISSIPPI...

...Southeast...

Francine has come inland over southern Louisiana but continues to
show a healthy circulation approaching the greater New Orleans
areas. Though some dry air has disrupted part of the core, intense
rainfall rates of 2-3.5"/hr are shown per MRMS, with storm totals
over 7 inches in south central LA. Rainfall tapers off notably to
the southwest of the center. Will maintain the Moderate Risk area
near the path of the center overnight given the likelihood of high
rainfall rates to continue as additional moisture is drawn in off
the Gulf across into southeastern LA and southern MS. The New
Orleans metro area will bear the brunt of the rainfall this evening
before translating northward, with the inflow band off to the east
responsible for the eastward bump in the outline. Francine will
continue inland overnight where the threat for excessive rainfall
extends northward trough much of Mississippi. Removed much of the
rest of Florida that was in a Marginal risk as lingering activity
should be diminishing over the next couple of hours.

...Intermountain West...

A deep layer cyclone moving across the northern Continental Divide
has brought afternoon convection and some flash flooding to parts
of Idaho into western Montana. Precipitable water values are
sufficient for heavy rain-related issues (0.75"), and the Slight
Risk area remains for portions of western MT and just into west-
central ID overnight. Hourly rainfall rates of 0.50-1.00" have been
observed and/or shown via MRMS which have been enough to reach
generally low FFG values in areas of complex terrain. With earlier
rainfall soaked in, additional rainfall may still exceed FFG values
overnight, but did trim off the western side of the risk area as
the focus should be mostly over western MT tonight closer to the
frontal boundary.

Fracasso


Day 2
Valid 12Z Thu Sep 12 2024 - 12Z Fri Sep 13 2024

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
MID-SOUTH & SOUTHEAST...

...Mid-South/Southeast...

21Z update... The latest guidance favored a general
south/southeast trend with the QPF footprint associated with
Francine from the previous cycle. As such, this resulted in WPC
increasing amounts across eastern Tennessee, northern and central
Mississippi, and northern and central Alabama. This uptick
increased the threat for excessive rainfall and flooding concerns
for both rural and some major metropolitan areas. The Slight Risk
area was trimmed a little eastward across eastern Arkansas but also
expanded to the south and east to encompass more of central
Mississippi, central Tennessee, and west-central and eastern
Alabama. The latest guidance also suggested an increase in feeder
band convection across the Florida Panhandle thus the Marginal Risk
area was extended 1-2 counties to the south.

Campbell

Francine is expected to be fully extratropical, with a well-
developed comma head and trailing front. Guidance suggests that MU
CAPE will be modest, 250-500 J/kg. Effective bulk shear should
continue to be sufficient for convective organization where enough
instability develops/exists. Precipitable water values remain
near 2", so hourly rain totals up to 1-2" should be possible, which
would be most problematic in urban areas and initially beneficial
elsewhere. This region has been quite dry lately. With the volume
of rain expected, and the concept of this being on the cusp of a
flash flood and longer duration flood event, kept the Slight Risk
area which showed minimal change from continuity. Across the
Southeast, there is a risk of training convection along Francine's
cold front which shows a greater signal for excessive rainfall
overnight. Broadened the risk area to encompass the possible
training rain band, as enough moisture, instability, and possible
stalling to be concerned about hourly rain totals to 3".

...Western MT, Idaho Stovepipe & Vicinity...

21Z update... Multiple impulses within the flow will trigger
showers and thunderstorms that will track across the Northern
Rockies region. PW values around 0.50-0.75 inches will be pooled
over the region throughout this period and will bolster rainfall
efficiency wit each passing impulse. Per the CAM guidance any of
these storms will be capable of producing periods of moderate to
heavy rainfall as they pass over the favored upslope areas and then
exit into the adjacent High Plains. There was a trend for
increasing QPF coverage and amounts across portions of the Hi-
Line. The Slight Risk area was expanded eastward to now include
more of north-central and northeast Montana and southwestward to
extend into portions western Montana and into Idaho.

Campbell

One or two surface lows are expected to lift northward this period
through MT, drawing in sufficient upslope flow, moisture, and
instability from the east to be concerned about the potential for
organized convection. The Slight Risk raised by continuity has been
maintained across portions of western MT. Hourly rainfall rates may
intensify up to 2 inches/hour during this period, with a few
isolated locations possibly accumulating up to 4 inches by the end
of the day.

Roth/Campbell
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FOUS30 KWBC 120838
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
438 AM EDT Thu Sep 12 2024

Day 1
Valid 12Z Thu Sep 12 2024 - 12Z Fri Sep 13 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF CENTRAL AND NORTHERN ALABAMA...

...Mid-South into the Southeast...
As of 08z Tropical Storm Francine continues to move northward out
of Louisiana and into Mississippi. The consolidated core of heavy
rainfall to the north of Francine will lift north across MS today,
and eventually into portions of far eastern AR and western TN by
this afternoon. This is the corridor that will likely see the most
widespread axis of 3-6" of rainfall. However rainfall rates along
this axis will generally be on the decline through the day. At 12z
we still may seeing some 1-2" per hour rainfall just north of the
center, but by 18z we are probably below 1" per hour for the most
part, and by 00z we may be struggling to even get 0.5" per hour.
Thus even though this axis has the highest HREF EAS probabilities
of 1,2 and 3", the flash flood risk is likely mitigated by the
lower rainfall rates. In fact despite the high QPF in the HREF, the
probability of exceeding 3 or 6 hr FFG in the HREF is negligible
over this area. Now 3-6" is still a lot of rain, and will probably
see some urban and perhaps small stream flooding, however currently
not expecting to see more widespread higher end impacts. Thus the
Slight risk should cover the threat.

The higher risk of flash flooding may actually end up well east of
Francine over portions of central and northern AL. Areal averaged
rainfall may be lower here than areas along the track of Francine,
but rainfall rates and upper bound rainfall potential is likely
higher. A narrow axis of enhanced convergence appears likely, with
south southwesterly flow east of Francine, and easterly flow from
the building high over the western Atlantic. This axis may stay
rather persistent though the period, with around 1000 j/kg of
instability advecting northward behind Francine as well. This
environment does appear conducive for possible training convective
bands and several high res model solutions suggest we do see
periodic training convective bands across this area by this
afternoon and evening. HREF neighborhood probabilities of exceeding
5" are 50-70% and exceeding 8" are as high as 30-40%. Not
necessarily expecting widespread coverage of these amounts, however
localized swaths of 6-10" of rain are a possibility today/tonight.
This could lead to locally considerable flash and urban flood
impacts. For this reason we have upgraded to a small MDT risk where
the conditional threat of high end impacts appears greatest.

Slow moving/backbuilding convection also appears possible today
over portions of the FL Panhandle. Model agreement on the
potential is not quite as strong as over AL, but certainly some
potential for higher end impacts here as outer banding east and
southeast of Francine could train/backbuild at times near the
coast. Given a bit more uncertainty and higher FFG here, we will
not upgrade at this time, but do consider this area as a higher end
Slight risk.

...Montana...
We did trim the Marginal and Slight risk areas some with this
update. Overall not convinced we will see much in the way of true
flash flooding today over MT. Instability is lacking over much of
the state which will keep rainfall rates generally below flash
flood thresholds. However with strong and persistent forcing the
latest WPC deterministic rainfall forecast is 1-3" near and just
south of Great Falls. If this occurs it would be an event that
falls in the 5-25 year ARI range. So despite weak rates rainfall of
this magnitude could certainly cause some areal flood concerns.
Over northeast MT there should be more instability and the
potential for rainfall totals over 1"/hr. Current indications
suggest this stronger convection would be progressive in nature
likely limiting the flood risk...however given the high PWs and
instability forecast could certainly see pretty impressive sub
hourly rates which could cause some flood concerns in any more
sensitive areas. Thus even though the Slight risk appears lower
end...we opted to maintain it over areas that may either see a
higher ARI longer duration rain or the potential for at least short
duration high rates.

Chenard


Day 2
Valid 12Z Fri Sep 13 2024 - 12Z Sat Sep 14 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE TENNESSEE VALLEY INTO THE SOUTHEAST...

By Friday the remnant surface circulation of Francine will likely
be somewhere near the AR/TN border. By this time the surface
feature will not be a main driver of heavy rainfall. However the
pattern will remain favorable for periodic training convective
bands from portions of TN into AL/GA and the FL Panhandle. While
the surface circulation of Francine will be dissipating, we will
still have plenty of mid level energy left over. Meanwhile we will
also have a trough of low pressure off the Southeast coast and a
high pressure to the north over the Western Atlantic. The
combination of these features will likely result in a corridor of
persistent low level convergence over TN/AL/GA. We should have
plenty of moisture and instability in place as well, and thus a
notable flash flood risk could continue. We will carry a higher end
Slight risk across portions of TN/AL/GA with this update.
Depending on what happens on day 1 (impacting soil and streamflow
conditions) can not rule out needing a MDT risk over a portion of
this area. However there is a bit more uncertainty on convective
details by Friday compared to Thursday, and so would like to
continue to evaluate future high res model runs, as well as see how
convection evolves today, before making any decision on an
upgrade. Either way flash flooding appears possible, and a locally
considerable threat could evolve.

Uncertainty increases with northeastward extent. There is some
flash flood risk over the western Carolinas, but unclear how far
northeast the risk will get. Quite possible the better convergence
and convective threat stays further west and southwest on Friday
as that appears to be the trend at the moment. Thus will only
carry a Marginal risk here. There is also some risk over the
coastal Carolinas where a low pressure may try to form offshore.
Again at the moment the most likely scenario sees the heaviest
rainfall stay offshore...however we could see some heavier
convective cells along coastal areas, warranting a Marginal risk.

Chenard
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FOUS30 KWBC 130755
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
355 AM EDT Fri Sep 13 2024

Day 1
Valid 12Z Fri Sep 13 2024 - 12Z Sat Sep 14 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF CENTRAL AND NORTHERN ALABAMA...

...Deep South...

Remnant circulation from Francine will be pivoting back south and
then southeast in retrograde thanks to a strong block from a stout
mid- level ridge positioned over the Great Lakes through
Ontario/Quebec. This will allow for the a migration of elevated
moisture centered under the disturbance to pivot back across MS/AL
where drier air has punched through under prevailing southwest flow
aloft, mainly above 500mb. This is well- documented within the 00z
sounding analysis out of KJAN where moisture is pooled between the
surface to 500mb with a large wedge of drier air focused above. The
sounding from KBMX was beginning to show signs of the dry tongue
and can be noted within the radar presentation as deep convective
development is struggling to initiate this evening. Tomorrow
afternoon and beyond is when the pattern shifts to a more favorable
convective regime across far Eastern MS into much of AL, especially
the northern 2/3's of the state thanks to the stacked synoptic
circulation sliding back overhead. Guidance is keen on the deeper
moisture return as indicated within the 700-500mb RH field leading
to an uptick in regional PWATs back above 1 deviation above normal
with ample mid- level energy accompanying.

The latest 00z HREF remains very aggressive within its depiction
for a broad axis of heavy rainfall in-of Northern and Central AL
during the late- afternoon and evening time frame in conjunction
with the increased upper forcing approaching from the west along
the tightened theta-E gradient located across much of the state.
Surface ridge to the northeast will also begin wedging south into
Northern GA with an axis of convergence developing upstream between
the approaching circulation from now Post-Tropical Francine. This
will place a good portion of AL into the crosshairs for a better
convective training episode as the deep layer flow aligns perfectly
from the southeast. HREF neighborhood probability for >5" is robust
between the area of KHUN down to KBHM indicating a 50-70% prob with
an EAS signal of 50-80% for at least 2", a signal correlated highly
for a higher end risk. Hourly rate probs are also aggressive in the
means with a corridor of elevated probs for between 2-3"/hr within
the HREF, along with some intra-hour rate potential exceeding 4"
given the efficient rainfall processes and expected instability
presence within the eastern fringe of the general circulation. All
these prospects weighted on the decision to maintain the inherited
MDT risk with some minor adjustments to correlate with the blended
mean QPF off the latest HREF, as well as the EAS prob field
coverage of higher probs for at least 2" of rainfall. The changes
made were not extensive in the grand scheme, so the overall
forecast was close to general continuity.

...Coastal Carolinas...

A weak inverted trough located off the Southeast coast will allow
for a targeted axis of heavy rainfall across the Eastern Carolinas,
mainly north of KCHS with a bullseye being forecast along the coast
of Southeast NC. The prevailing easterlies off the Atlantic within
the integrated water vapor field (IWV) from the GFS signal the axis
very well with a nose of elevated PWATs being advected right into
the coastal areas of NC during the first half of the period. 00z
CAMs also signal the threat for a period of heavy rainfall with
some varying degrees of the latitudinal push of where the heaviest
precip would occur. The greatest probabilities for >3" are centered
from Wilmington up through Morehead City into Cape Hatteras.
Considering the area FFG's, the main flooding risks will be
relegated to more urbanized areas where run off potential is
highest. The signal was good enough for a continued MRGL risk with
some expansion further inland, mainly west of Raleigh where some
convergence from the damming high to the north and the prevailing
easterlies may intersect allowing for a small axis of enhanced
precip away from the coastal plain. Not anticipating a large areal
coverage of flash flooding in any case for the region, but a few
pockets are plausible leading to a low to middle ground MRGL for
the forecast.

...Florida Panhandle...

Deep tropical flow pulling north from the Gulf will allow for an
axis of heavy convection to push north out of the Gulf into the Big
Bend of FL. Areal FFG indices for 1/3/6 hr rates are pretty
substantial, so the threat is low-end within the MRGL risk
category. Still, the signal for amounts >5" is relatively high
right along the coast leading to the MRGL continuation from
previous forecast.

Kleebauer


Day 2
Valid 12Z Sat Sep 14 2024 - 12Z Sun Sep 15 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHEASTERN U.S...

...Southeast...

The remnant mid and upper circulation from Francine will get stuck
under the blocking pattern positioned across the northern and
eastern U.S with little propagation of any kind during the period.
This will allow for a continuation of broad, cyclonic flow across
the Southeast with a steady convergence pattern positioned over
parts of the Deep South. A steady southeast flow pattern will
preside over much of AL and Western GA with a sharp convergence
signal focused over the central portion of the outlined area thanks
to the persistent anti-cyclonic "wedging" occurring around the
southern flank of the ridge, banking against the cyclonic regime
centered around Francine's remnants. Ensemble QPF distribution is a
bit further south compared to the previous forecast allowing for an
adjustment in that direction for the SLGT risk prospects. Totals
are generally favored to be within 1-3" overall, but some pockets
of higher totals are depicted within the 00z deterministic suite
leading to some locally impactful flash flood prospects, especially
when coupled with the previous period(s) of rainfall lowering the
area FFG's across AL/GA.

The SLGT risk is on the higher-end of the spectrum with a higher
risk potential relying on the contingency of how the D1 period
plays out across the region. There's a non-zero chance of an
upgrade, but the slowly degrading axis of instability may thwart
the potential all together. Regardless, the SLGT risk is sufficient
just given the variables at hand.

...Arizona...

A surge of deep tropical moisture from now Tropical Storm Ileana
will make progress into the southern portion of AZ by the middle to
end of the forecast period. With sufficient diurnal heating
Saturday afternoon, environment across Southern and Southeast AZ
will destabilize allowing for isolated to scattered thunderstorms
to initiate in-of the terrain situated within Pima/Santa Cruz
counties to possibly as far east as Cochise county in proxy to the
Huachuca mountains. MUCAPE forecast is relatively favorable for
convective development with the ensemble SBCAPE forecast between
750-1250 J/kg off the latest HREF mean. The combination of
increasing moisture anomalies and environmental buoyancy adds
favor to an isolated flash flood risk, especially within the
terrain and adjacent locales. A MRGL risk was maintained from
previous forecast, but trimmed on the northern edge given the
expected timing of the moisture push to be delayed for a greater
convective threat within Pinal/Maricopa counties. This area will
have more favorability later on D3.

Kleebauer
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FOUS30 KWBC 140809
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Sat Sep 14 2024

Day 1
Valid 12Z Sat Sep 14 2024 - 12Z Sun Sep 15 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHEASTERN U.S...

...Southeast...

Current radar/satellite composite depicts a broad cyclonic gyre
situated across the Southeastern U.S with a north-south band of
convection bisecting the a good portion AL into Western TN around
the northeast periphery of the remnant cyclone. The surface
reflection from what was Francine will become more diffuse over the
next 6 hrs with a degrading surface signature, leaving much of the
flow tied to the leftover mid and upper lows associated with the
storm. That said, the cyclonic spin from the tandem 850-500mb
low(s) will allow for a continued favorable moisture stream around
the circulation with small mid-level perturbations stuck over the
same areas allowing for locally enhanced ascent within the confines
of AL/GA/TN. PWATs generally residing within the +1 standard
deviation anomaly across the Deep South will be sufficient enough
within the pattern to yield another round of scattered to
widespread convection across similar areas that were impacted
today. The difference is the magnitude of the convective pattern
will be a bit less vigorous thanks to the weakening mid and upper
low centers as denoted within all the recent guidance height
fields. Still, the combination of the moisture anomaly and semi-
favorable ascent under the remnant mid and upper lows will be
plenty to offer another round of convection across the Deep South.

To the northeast, a stout surface ridge will nose down further into
the interior Southeast with a formidable easterly regime focused
in-of Northern GA down into the Northwest side of AL. The
combination of the cyclonic flow from the mid-level remnants and
wedging associated with the surface ridge will create a tightened
axis of convergence within the state of AL down into Western GA.
The consensus this evening within the 00z CAMs suite was very well
represented within the HREF mean QPF and associated probability
fields, highlighting the semi-narrow corridor of higher rainfall
potential located just to the south and west of Huntsville,
bisecting much of North-Central AL down into the Southwest side of
GA. This area has been the beneficiary of some significant rainfall
the past 24-48 hrs leading to a degraded FFG footprint where flash
flood prospects will be greater, relative to average. Signals for
1-2"/hr rainfall rates would be sufficient given the antecedent
conditions across the area, and with the setup likely to garner
some locally enhanced rainfall rates >2"/hr as indicated within the
prob fields, there's a higher likelihood for continued flash flood
concerns within the confines of those areas in AL and GA mentioned
above. A higher end SLGT risk is the forecast for those areas
extending from Northwestern AL near the AL/MS line, southeast
through Columbus, GA, an area that includes the Birmingham metro.
SLGT risk extends further northwest and southeast, respectively
with a broad MRGL extension around the periphery as heavy rain
concerns exist from as far north as Western KY to as far Southeast
as Northeastern FL.

...Arizona...

A surge of deep tropical moisture from now Tropical Storm Ileana
will make progress into the southern portion of AZ by the middle to
end of the forecast period. With sufficient diurnal heating
anticipated this afternoon, the environment across Southern and
Southeast AZ will destabilize allowing for isolated to scattered
thunderstorms to initiate in-of the terrain situated within
Pima/Santa Cruz counties to possibly as far east as Cochise county
in proxy to the Huachuca mountains. MUCAPE forecast is relatively
favorable for convective development with the ensemble SBCAPE
forecast between 500-1250 J/kg off the 00z HREF mean. The
combination of increasing moisture anomalies and environmental
buoyancy adds favor to an isolated flash flood risk, especially
within the terrain and adjacent locales. A MRGL risk was maintained
from previous forecast with only minor adjustments based within the
HREF blended mean QPF footprint, and aligning with the edges of the
10% or great probabilities within the neighborhood probability
output for >2" rainfall potential. This area will have more
favorability later on D2.

...South Florida...

Surface trough located in-of South FL will maintain a prevailing
westerly flow across the Southern part of the Peninsula, placing
the mean steering pattern pointed towards the population centers
along the Southeast FL coast in time for the sea breeze convective
initiation this afternoon. Area PWATs are very elevated this
evening with the 00z sounding out of KMFL depicting a solid 2.40"
PWAT reading placing the area within the +1-2 standard deviation
anomaly for the period. This environment will be conducive for
convective generation just inland along the penetrating sea breeze
in the afternoon with locally strong convective cores producing
rainfall rates between 2-3"/hr on initiation, moving towards the
coast thanks to the prevailing steering flow. HREF probabilities
for >3" are solidly between 50-80% along the population centers
extending from PBI down through MFL with the highest probs situated
between PBI and FLL. Lower end 5+" probabilities are also
highlighting the area of interest, so the threat is within the
middle grounds for flash flood concerns leading to an addition of a
MRGL risk situated along the Southeast FL coast encompassing the
population centers.

Kleebauer


Day 2
Valid 12Z Sun Sep 15 2024 - 12Z Mon Sep 16 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST U.S...

...Southeast...

Despite the remnant mid and upper circulation from Francine
degrading in its presentation, another period of enhanced
convective activity will spawn underneath the primary upper forcing
lingering over the Southeastern U.S. There's a bit more emphasis on
an axis of convection developing across portions of the Lower
Mississippi Valley in-of AR and MS, extending southeast into parts
of the Deep South, mainly Southern MS and AL. Areal PWATs will
remain elevated within +1 standard deviations, enough of an anomaly
to spur up some potential heavier convective cores that could
result in some flash flood prospects, especially over any urban
zones where run off potential is greatest. Ensemble bias corrected
QPF and the 75th percentile of the NBM indicate a fairly stout axis
of heavier precip likely to occur under the influence of the upper
low and remnant energy pivoting around the general circulation. The
primary concerns will continue to be those locally heavy rates that
will reach between 1-2"/hr with some intra-hour potential for
heavier rates that typically cause more issues in this part of the
country. A SLGT risk was added to the previous forecast with an
adjustment southwest to the overall SLGT/MRGL risk areas to align
with the current trends and ensemble forecast consensus on the
heaviest precip location. The MRGL expands into the FL Panhandle to
cover the area that has been hit pretty hard in the past 36 hours
as isolated storms are still forecast for those areas that have
seen copious amounts of rainfall in the above time span.

...Southwest...

Remnant moisture from now Tropical Storm Ileana will continue to
advect northward into the rest of the Desert Southwest with a
trajectory towards the Four Corners, wrapping back eastward into NM
during the afternoon hours Sunday. The ensemble QPF footprint upped
the total precip forecast compared to the previous periods, a trend
that was noted when assessing the QPF differential from 12z to 00z.
This places the convective pattern towards those areas we've been
highlighting all summer for flash flood concerns thanks to a
plethora of burn scars located within the terrain across parts of
NM. The previous forecast was relatively unchanged over AZ into the
Four Corners, but the MRGL risk was expanded to include much of NM
with a focus into the terrain over the Sangre de Cristos and the
Sacramento Mountains. General QPF average between 0.25-0.75" is
expected, but maxima of >1" will be plausible anywhere within the
confines of the forecast risk area. A targeted SLGT risk is still
possible, but the scattered nature of the convection forecast
doesn't instill enough confidence at this time. A reassessment with
the addition of CAMs guidance could sway that the other way, so
stay tuned for future updates.

Kleebauer
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FOUS30 KWBC 150911
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
511 AM EDT Sun Sep 15 2024

Day 1
Valid 12Z Sun Sep 15 2024 - 12Z Mon Sep 16 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL GULF COAST INTO THE MISSISSIPPI...

...Central Gulf Coast into MS...
The setup that has resulted in a convective bands and locally
heavy rainfall the past couple days will continue today, just
shifted a bit to the southwest. Lingering mid level energy and low
level convergence will result in convection today from coastal AL
northwestward across MS and into eastern AR. The persistence of the
convergence will allow for some training/backbuilding potential
locally increasing rainfall totals. The overlap of strongest
convergence and higher instability looks to focus closer to the
Gulf Coast today, across portions of coastal MS/AL and the western
FL Panhandle. The flash flood risk is likely highest across these
areas, with 5"+ HREF neighborhood probabilities as high as 50-80%.
HREF guidance indicates one round of potential backbuilding cells
this afternoon, with another round possible late tonight into
early Monday. Given this signal the Slight risk was expanded into
this region, and do consider this area to be a higher end Slight
risk, with locally significant flash flooding a possibility given
what should be very efficient rainfall producers.

The flash flood risk is a bit lower further north across MS and AR
given weaker instability and what should generally be more
transient convective cells. Nonetheless some training/backbuilding
is still possible, and soil saturation is still above average due
to rainfall from Francine a few days ago. Thus still think a
Slight risk is warranted, with isolated to scattered flash flooding
possible.

....Coastal Carolinas...
An area of low pressure off the southeast coast may bring heavy
rainfall into portions of coastal SC/NC between 06z-12z Monday. The
GFS remains a fast outlier in bringing heavy rainfall inland from
this system, and thus is not a preferred solution. While there is
still some spread amongst the other model solutions, some form of
consensus is developing. This consensus would suggest that some
bands of locally heavy rainfall may get into coastal portions of
the Carolinas early Monday. Still think the greater flash flood
risk ends up after 12z Monday, but can not rule out some heavier
totals right along the coast by 12z...and thus will introduce a
Marginal risk.

...South TX...
A small Marginal risk was added to far southern TX. Will likely be
an active convective day across northeast MX today, with easterly
low level flow advecting in moisture off the Gulf, and westerly
mid/upper flow bringing in tropical moisture off the Pacific. Low
level convergence should be enhanced in this pattern, and also
have some mid/upper level energy to work with as well. In general
expect the bulk of convective activity to be over northeast MX
where convergence is strongest, however there is at least some
threat far south TX can see some activity as well. Guidance
indicates that any convection that organizes over south TX should
drop back south into MX, however there is an opportunity for some
slow moving cells later this morning or afternoon before this
propagation takes hold.

...Southwest...
A Marginal risk covers portions of AZ and NM today where a
localized flash flood risk may exist. This risk area was reduced in
size to just cover areas where convective coverage should be a bit
greater and instability more pronounced. Rainfall over the
Marginal risk area could locally exceed 1" which could produce an
isolated flash flood over any more susceptible basins.

Chenard


Day 2
Valid 12Z Mon Sep 16 2024 - 12Z Tue Sep 17 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CAROLINAS INTO FAR SOUTHEAST VIRGINIA...

...Carolinas into Virginia...
An area of low pressure will likely move into portions of NC on
Monday bringing a heavy rainfall threat to the area. Confidence is
increasing that this system will have a notable core of heavy
rainfall near the center and heavy convective banding to the east
of the center. The threat of flash flooding across portions of
eastern NC appears to be increasing, with locally significant
impacts possible. With that said there remains some model spread
regarding the location of landfall and the structure/intensity of
the system.

Like was mentioned in the day 1 discussion, think the 00z GFS
remains a less likely fast and west outlier with this system on
day 2. After discounting that solution the overall model consensus
improves, although not without some notable spread. The 00z NAM
and Gem Reg are two of the stronger and further south solutions,
with the 00z CMC and UKMET further east over coastal NC. With the
high res models you have the 00z 3km NAM and ARW stronger/quicker
and further south near the SC/NC border, and the HRRR and ARW2 a
bit slower/weaker and north. Overall it appears that the earlier
the low begins to deepen the stronger, quicker and further south it
moves ashore. Where as the models with a slower developing low
keep it a bit weaker and east over NC. At the moment do not really
have a strong preference, with things likely becoming clearer today
as the low begins to become more well defined offshore.

The above described uncertainties will keep us from upgrading to a
MDT risk at this time. However do consider this a higher end
Slight risk across portions of southeast NC. Wile the details still
need to be ironed out, what we can say is that the flash flood
risk from this system is increasing and locally significant flash
flooding is possible over portions of eastern NC (and possibly
northeast SC depending on the track). Just about every model
solution brings a low pressure ashore with locally heavy rainfall
near and east of the center...however enough spread still exists
with the track and intensity of the system to keep the risk level
at Slight for now. Once the low develops and confidence on the
evolution of the system continues to increase, a MDT risk upgrade
may be needed.

...Central Gulf Coast...
Some flash flood risk will likely linger across portions of the
central Gulf Coast into southeast AR on Monday. However the pattern
becomes gradually less favorable with time, and thus currently
expecting that only a localized flash flood risk will linger into
Monday.

...Southwest to Four Corners... A strong deep layered low moving
into the CA will result in an uptick in large scale forcing over
portions of the Southwest on Monday. Broad south to southwesterly
flow ahead of this feature will also advect moisture into the
region, and should have plenty of instability and moisture in
place for locally heavy rainfall within convection. Given the
increased forcing convective coverage should be notable over the
region, suggesting at least an isolated flash flood threat. Cell
motions should be fairly quick off to the northeast limiting the
duration of heaviest rainfall and the overall flash flood risk.
However with the persistent forcing in place areas could see
multiple convective cells/clusters move through over the period
adding to rainfall totals.

...NV/ID...
An axis of higher areal averaged rainfall is likely closer to the
stronger forcing underneath the deep layered low over portions of
northern NV, southeast OR and into ID. On Monday morning there is
some signal for potential training rainfall bands over portions of
NV, although instability looks rather weak, suggesting rainfall
rates may struggle to get high enough for flash flooding.
Nonetheless will need to be monitored and some areas of 1-2" of
rainfall are possible, which for some of this area could be around
a 5yr ARI event. Thus even without higher rates some areal flooding
is a possibility. By Monday afternoon we should see some increase
in instability over the broader region likely allowing for some
heavier convective cells. However currently expecting these cells
to be rather quick moving. Thus overall think a Marginal risk
should suffice, with localized flooding concerns a possibility.

...ND/MN...
A Marginal risk was added across portions of ND and MN. Model
guidance shows a lifting warm front, mid level vort energy moving
through, and divergent flow aloft between two jet streaks...likely
enough forcing to get convective development Monday into Monday
night. Convective details differ from model to model, but the
overall ingredients are similar and instability should be
plentiful. Overall the threat is there for an axis of training
and/or backbuilding convection within the Marginal risk area, and
some flash flooding could evolve.

Chenard
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FOUS30 KWBC 160829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Mon Sep 16 2024

Day 1
Valid 12Z Mon Sep 16 2024 - 12Z Tue Sep 17 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER SOUTHEASTERN
NORTH CAROLINA AND THE NORTHWESTERN CORNER OF SOUTH CAROLINA...

...Carolinas...

PTC8 continues to churn off the Carolina coast with an ill-defined
center of circulation and convective clustering to the north of
the analyzed low off the coast of SC. The beginning wave of
tropical rainfall has started across Northeast SC into Southeast
NC with rates anticipated to pick up as the deeper tropical
moisture flux located offshore begins to propagate into the coast.
There has been relatively modest uncertainty to exactly where the
heaviest rainfall will occur due to a less defined surface low
center that provides more consensus on the specific track and
subsequent heavy rain axis. One of the notable observations through
the past 6-8 hrs has been the QPF shield displaced further north
away from the analyzed surface center provided by NHC. A lot of
this is likely due to the moderate shear impinging the southern
flank of the circulation allowing for an offset of the precip field
to the north and northeast of the primary circulation. This has
caused issues within the NWP suite of forecasts, especially higher
resolution guidance that tends to need a more defined surface
initiation to outline short range prospects within the precip
field and track of the surface reflection. There is enough data to
project the current QPF swath to be displaced further north than
some of the CAMs and global deterministic output with a surface
reflection likely to come ashore a bit further north than even the
00z consensus. For that, the trend is for 4-8" totals with locally
up to 10" possible across the Northeastern corner of SC through
Southeast NC, an agreed axis within the neighborhood probability
fields from the latest HREF. The signal for >5" is very robust with probabilities between 70-90% located across Southeastern NC with
the strongest signal located near Wilmington, an area of greatest
concern considering the urbanization factors.

The storm will induce some pretty good rainfall across Northern SC
and much of NC through the periods as the circulation moves inland
and progresses westward into the Carolina Piedmont. Bands of
tropical rainfall with efficient warm rain processes will pivot
inland with the prospects of flash flooding increasing over areas
that see training. As a result, a broad SLGT risk is centered
across much of North Carolina and the northern periphery of South
Carolina. A targeted MDT risk is in place over the northeast corner
of SC and much of Southeastern NC as the consensus for higher
rainfall amounts is most prolific within that zone.

...Northern Plains and Upper Midwest...

Aloft, a shortwave will eject out of the Central Plains and push
quickly to the northeast, entering the Northern Plains of the
Dakotas into Northwestern MN by later this evening providing ample
mid-level ascent conducive for convective initiation. At the
surface, a pre-frontal trough will develop in-of the Southern
Canadian Prairies, shifting southward into Northern ND and MN by
early this evening, setting the stage for a strong surface
convergence axis located across Eastern ND and Northwest MN. This
is thanks to the tandem mid-level ascent pattern and convergence
signature located within a formidable theta-E tongue bisecting the
area. The signal has grown considerably in the past succession of
runs with the latest CAMs all generally robust with its
presentation of locally enhanced rainfall located over the above
regions. With the mean flow generally parallel to the pre-frontal,
surface based trough, there is a growing concern for training cells
that develop upstream over ND and progress east-northeast along the
slow-moving trough axis. The 00z HREF blended mean QPF is quite
robust in its depiction with an areal average of 1.75-2.5" of total
precip located from just west of Grand Forks up through the
International border in Northern MN. A bullseye of 3-5" is co-
located within the axis of the surface trough positioning extending
over much of Northwestern MN, an area that typically does not favor
these types of convective outputs. HREF EAS probabilities for 1"
(80-90+%) and 2" (30-50%) are incredibly high for an event that is
not tied to a strong organized synoptic complex, only adding
emphasis to the potential with such high agreement within this
evenings CAMs. Neighborhood probs are just as impressive with a
strong >3" signal (70-90+%) and modest >5" (15-30%) output with the
latter tied closer to the Canadian border where the model agreement
is strongest for the heavier totals. A SLGT risk was added given
the favorable forecast from this evening and a strengthening
consensus amongst CAMs members for a locally enhanced flash flood
threat across the northern tier of the ND/MN area.

...Western U.S...

Upper air analysis indicates a broad closed upper circulation
positioned over Northern California with an expectation to
strengthen as we progress through the period. Increasing moisture
on the eastern flank of the mean trough will allow for a better
convective environment as the region enters a strong upper forcing
regime with a correlated instability maximum located over the Great
Basin. The approach of the upper low will initiate a blossoming of
convection across the Eastern and Northern Sierra, extending into
NV and eventually ID as we progress through today and this evening.
MUCAPE between 500-1000 J/kg will be most common within the
interior, plenty to induce a swath of enhanced convection over an
area not typically acclimated to see a decent amount of rainfall.
The current forecast calls for a multi-region impact of
convectively driven rainfall that could easily exceed 1" in any
area located from the Great Basin, Four Corners, and portions of
the Southwestern U.S. A fairly robust and widespread probability
for >1" (70+%) is well documented within the 00z HREF neighborhood
probability output over the above locations, a strong enough signal
to warrant a continuation of the previous MRGL risk forecast.

...Deep South...

Lingering low-level moisture with the proximity of a quasi-
stationary front across the Deep South will allow for another
period of locally enhanced rainfall that could cause some flash
flood concerns, generally over the Lower Mississippi Valley into
the Central Gulf coast. The signal is more diffuse than previous
periods, but the probability fields still indicate a formidable
potential for >3", especially along the Gulf coast where the
surface based instability is most prominent. This is a low-end MRGL
risk with a better chance for flash flooding to occur over those
areas that have been hit hardest the past several days from
Francine and its remnants.

Kleebauer


Day 2
Valid 12Z Tue Sep 17 2024 - 12Z Wed Sep 18 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID ATLANTIC, FLORIDA PANHANDLE, SOUTHERN ROCKIES, AND WESTERN
MONTANA...

...Mid Atlantic...

The remnant cyclone will be perusing through the Mid Atlantic come
Tuesday with its moisture flux steadily pushing northward through
the Central Mid Atlantic, carrying a potential for locally enhanced
rainfall and flash flood prospects. As of this time, the consensus
is still muddled on exactly where the remnant circulation will be
progressing, as well the forecast instability positioning on the
eastern flank of the circulation. PWAT anomalies will be creeping
closer to 1-2 standard deviations above normal, a historical
characteristic for heavy rain and flash flood concerns within the
Mid Atlantic. Ensemble instability fields are generally more
defined in-of the Blue Ridge in VA and across Southeastern VA.
These would likely be the areas with the most interest when it
comes to any higher risk. The shifts within the ensemble mean QPF
add too much variance to conclude the prospects for a higher risk,
at this time. With coordination from the local WFOs across the Mid
Atlantic, a MRGL was maintained from the previous forecast with
some adjustments based on the latest ensemble QPF footprint.

...Florida Panhandle...

Lingering low-level moisture flux tied a quasi-stationary front and
subsequent weak surface reflection along the Gulf Coast will allow
for one more period of isolated to widely scattered thunderstorms
within the Western FL Panhandle, bisecting an area that is
currently under more sensitive FFG indices compared to
climatological averages. The most prone location resides near
Apalachicola where recent 5-day rainfall totals are upwards of
8-15" leading to a fairly water-logged position along the immediate
Gulf coast. Despite the signal not being as impressive as previous
periods, the instability gradient right along the coast could
provide the necessary element to maintain a risk for locally heavy
rainfall, especially any cells tied to the boundary running
parallel to the coast. This is a lower-end MRGL risk categorically,
but with forecasts within the deterministic still pointing towards
cells producing >2" of rainfall, this was enough of a signal to
warrant the MRGL risk inherited from the previous forecast.

...Southern Rockies...

Ejecting shortwave trough out of the Four Corners will provide
ample mid and upper support for a generation of scattered
convection located across the Southern Rockies down into the
Sacramento Mountains in NM. The setup is geared towards locally
enhanced rainfall prospects tied to the terrain with the best
opportunity for impacts likely occurring over burn scars located
within the Sangre de Cristos and the Sacramento Mountains near
Ruidoso. Those two locations are very sensitive, and the setup
would certainly be conducive to providing local impacts within the
two separate MRGL risk areas. Areal QPF average is between
0.25-0.5", but deterministic output still signals potential for
upwards of 1.5-2" of rainfall, plenty to cause issues within the
complex terrain and over any sensitive grounds. A MRGL risk was
added over the above locations to account for the threat.

...Western Montana...

Approaching closed upper low over the Great Basin will pivot
northeastward while tilting negative as it progresses into the
Interior Mountain West, eventually situating over MT by the end of
the forecast cycle. Large scale ascent pattern will be maximized
downstream of the mean trough with ample mid-level moisture
advection being carried poleward into Big Sky Country, pushing PWAT
anomalies into the +2 to +3 standard deviation range. This is a
prominent signal when coupled with a strong upper forcing regime
and is co-located with an increase in boundary layer instability
when assessing the area MUCAPE field(s). Current QPF distribution
signals a scattered array of 1-2" totals with the most precip
footprint of the maxima tied closer to the terrain thanks to the
orographic elements typically favored in these types of setups. The convectively driven pattern is one that maintains prominence on
local flash flood prospects and still has some room for a targeted
higher risk pending the convective outlook once into better range
of the CAMs. For now, maintained general continuity with some
extension on the southern periphery of the risk area over MT.

Kleebauer
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FOUS30 KWBC 170800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Tue Sep 17 2024

Day 1
Valid 12Z Tue Sep 17 2024 - 12Z Wed Sep 18 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER SOUTHEAST VIRGINIA...

...Mid Atlantic...

The disturbance that pushed ashore yesterday will continue to churn
over the Southern Mid Atlantic with a funneling of moisture off the
Atlantic aimed across far Northeastern NC and the adjacent VA
Tidewater through the morning and afternoon hours. Modest SBCAPE
located across the above areas will justify enough instability to
trigger heavier convective cores capable of producing heavy
rainfall in an area that has a historically lower FFG due to the
urbanization factors over places like Norfolk, Virginia Beach, up
to Williamsburg. The pattern has produced a relatively robust precip
footprint as it is with models struggling to handle the overall
magnitude of the rainfall on the eastern flank of the low. 00z HREF
probability fields are still pretty exuberant for >3" (50-70%)
across the Tidewater with an extension of 30-50% further inland
towards Richmond. PWAT anomalies are sufficiently around +2
standard deviations with the 00z sounding out of MHX producing an
observed PWAT of 2.27", a similar airmass that will be advecting
north with time. This pinpoints the Southeastern VA area as the
most notable area for potential flash flood capabilities for the
period when you couple the moisture anomalies and anticipated areal
instability presence for tomorrow. This allowed for a general
maintenance of the SLGT risk from the previous forecast with only
an minor adjustment necessary on the western and northern flank of
the risk area.

Across the rest of Western NC and Western VA, the general
circulation of the remnant low will drift into the Carolina
Piedmont and become fairly stationary over the course of the
forecast. The weakening of what's left over from the disturbance
will mitigate the precip field enough to limit the flash flood
concerns further inland, although still within the low end of the
MRGL risk. In fact, some of the 24 hr totals within the means are
pretty high across Western NC and VA, but a lot of the rainfall
comes from a persistent, steady light to moderate rain with
embedded heavier echoes during the afternoon and evening hours with
marginal diurnal destabilization. Forecast 1"/hr rainfall
probabilities are relatively tame with basically no calls for 2"/hr
within the prob fields. The signal was sufficient to maintain the
MRGL for the forecast with most of the rain accumulating over a
long period of time and not so much a classic flash flood prospect.
Those areas along the Blue Ridge into the Shenandoah will have the
best opportunity for flooding in this setup, but with higher FFGs
across the region, the prospects are lower than normal for a
heightened flash flood concern.

...Florida Panhandle...

Lingering low-level moisture flux tied a quasi-stationary front and
subsequent weak surface reflection along the Gulf Coast will allow
for one more period of isolated to widely scattered thunderstorms
within the Western FL Panhandle, bisecting an area that is
currently under more sensitive FFG indices compared to
climatological averages. The most prone location resides near
Apalachicola where recent 5-day rainfall totals are upwards of
8-15" leading to a fairly water-logged position along the immediate
Gulf coast. Despite the signal not being as impressive as previous
periods, the instability gradient right along the coast could
provide the necessary element to maintain a risk for locally heavy
rainfall, especially any cells tied to the boundary running
parallel to the coast. 00z HREF neighborhood prob output signals a
stripe of 25-50% in any given location across the I-10 corridor
down towards Apalachicola for >3" potential with a 10-15% prob for

5" over the same area. The convective coverage is more scattered

in nature, so the previous MRGL has merit given the probabilities
and anticipated rates hovering between 1-2"/hr.

...Southern Rockies and High Plains...

A strong, broad upper low over the Great Basin will continue to
slowly migrate to the northeast with increasing large scale forcing
downstream of the mean trough. Model consensus has grown over the
past succession of runs for a broader ascent pattern to develop
across the Southern Rockies with some aid of modest surface based
instability and terrain to generate a period of convection
beginning later this afternoon and early evening. Further east into
the NM and TX High Plains, a region of relatively favorable SBCAPE
between 500-1500 J/kg will allow for convection to develop
downstream of the mountains with cells becoming rooted at the
surface and helped along by shortwave energy ejecting out of the
adjacent terrain. 00z CAMs are more robust with the convective
pattern than even 24 hours ago, matching well with the recent ML
output from the ECMWF AIFS and Graphcast with some precip focus
over those areas. The HREF probs for >1" were much higher than
previous forecast as a result with some lower end probs for >2" and

3" located across parts of the Southern Rockies and High Plains.

The focal points for flash flooding potential will continue to be
the complex terrain and burn scars situated within the Sangre de
Cristos along with the Sacramento Mountains, further south. The
High Plains area is low-end within the MRGL risk threshold, but the
favorable pattern lends credence to the chance at an isolated cell
or two over-performing and causing some flood concerns. This also
matches the current UFVS First Guess Field forecast for the period
allowing for the two previous MRGL's in the region to be bridged
together and expanded east to account for the threat.

...Northern Rockies and High Plains...

Approaching closed upper low over the Great Basin will pivot
northeastward while tilting negative as it progresses into the
Interior Mountain West, eventually situating over MT by the end of
the forecast cycle. Large scale ascent pattern will be maximized
downstream of the mean trough with ample mid-level moisture
advection being carried poleward into Big Sky Country, pushing PWAT
anomalies into the +2 to +3 standard deviation range. This is a
prominent signal when coupled with a strong upper forcing regime
and is co-located with an increase in boundary layer instability
when assessing the area MUCAPE field(s). The latest 00z
deterministic and relevant ensembles, including the HREF provide a
strong consensus on the potential for locally heavy rainfall
extending from Western MT, where the signal is the strongest, over
into the High Plains of Eastern MT and points south near the Bad
Lands of SD. Ensemble QPF output is still within that 1-2" range
for an areal average, but pockets of higher QPF are dispersed all
across the above area thanks to the approach of the potent mid-
latitude cyclone. Considering the overall setup and growing
convective support of the CAMs downstream of the previous MRGL
risk, the risk area was expanded to include much of the rest of MT
down into Northeast WY and Western SD, areas that have more
favorability for flooding potential due to lower FFGs and higher
run off capabilities given the soil type and topographic makeup in
those locations.

A SLGT risk was mulled over for Western MT, but with coordination
from the local WFO in Great Falls, decided against the upgrade with
retaining focus for the higher impacts anticipated the next period
(Wednesday).

Kleebauer


Day 2
Valid 12Z Wed Sep 18 2024 - 12Z Thu Sep 19 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF MONTANA...

Negatively tilted mean trough and closed low over the Northern
Rockies will become vertically stacked over Big Sky Country leading
to a prolific axis of deformation developing in-of the Northern
Rockies encompassing Northwest MT. Ensemble mean QPF is quite
impressive given the synoptic regime with very little surface based
instability to work with. The whole pattern is driven by powerful
upper forcing within a well-defined axis of deformation on the
western side of a broad, occluding surface cyclone. Precip totals
off the latest deterministic are gaudy with a wide swath of 2-4"
with locally as high as 5+" located within the terrain to the east
of Great Falls. There has been some adjustments within the ensemble
means for the heaviest axis of QPF with a small displacement to the
east. When assessing the 500mb height anomalies between ensemble
runs and the current deterministic, there is a subtle, but
noticeable difference in the closed upper reflection being a bit
more into East-Central MT leading to a heavier QPF distribution
being a bit further east than previous iterations. This also
follows with the ML outputs recently with the trend having the axis
of deformation a bit further east of Great Falls, a general marker
for where the heaviest precip will focus. Ensemble bias corrected
QPF is also a touch east with totals relatively similar in the 2-4"
range with a max of just over 5". This will be something to
monitor going forth, but the signal is still very much present for
a locally impactful rainfall thanks to a strong mid-latitude
cyclone entering the interior Northern U.S. A SLGT risk was
maintained with a small extension eastward to reflect the recent
trends in guidance.

Kleebauer


Day 3
Valid 12Z Thu Sep 19 2024 - 12Z Fri Sep 20 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer
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FOUS30 KWBC 180753
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
353 AM EDT Wed Sep 18 2024

Day 1
Valid 12Z Wed Sep 18 2024 - 12Z Thu Sep 19 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF MONTANA...

...Montana...

Current WV satellite imagery is a sight this evening with a broad
upper circulation engulfing much of the Inter Mountain West through
Big Sky Country in MT. Height falls have been impressive with this
disturbance as it pivots northeastward with an intensifying
dual surface low reflection located across Central MT with
pressures now down below 1000mb. The expectation is for the
cyclone to continue to intensify through the evening with an
occlusion phase occurring later this morning allowing for a strong,
well- defined deformation axis to center itself over the Northern
Rockies, east of Great Falls. PWAT anomalies approaching the upper
end of climatological peak for not just this time of year, but all
years according the latest NAEFS and ECENS moisture return
intervals. PWAT anomaly forecast is between +3 to +5 deviations, a
solid 97th to 99th percentile outcome given climatology which is
impressive to say the least. The strong large scale forcing
focused on the western side of the occluded cyclone will induce a
focused TROWAL across the aforementioned area above, in good
agreement amongst all guidance, including the CAMs and global
deterministic. Regardless of which model output you assess, the
prospects for 3-5" of rainfall with locally higher are being
forecast in-of the terrain east of Great Falls and the I-15
corridor in MT.

Latest HREF probabilities are pretty stout within both the
neighborhood and EAS fields across that general area with the
neighborhood probs running between 50-80% for >5" and even some
15-30% probs for the >8" totals being expressed. EAS probabilities
are >80% for at least 2", a testament to both the expected rainfall
and the consistency among the CAMs. This is no different from the
totals expressed within the global deterministic, and even the
ensemble blends are signaling over 4" in places. The bottom line
is; this will be a pretty formidable storm for the Northern Rockies
and adjacent Great Plains of MT with scattered instances of
flooding increasingly likely as we move through the daytime,
Wednesday. The storm will drift north and begin losing steam the
back end of the forecast leading to the organized TROWAL to fade
with lighter rates before tapering off later in the evening. The
previous SLGT risk was maintained given the strong continuity from
guidance. The only limitation to this being a higher risk is the
lack of sufficient surface instability with most of the positive
buoyancy relegated above the boundary layer. Still, rates of
1-1.5"/hr are still possible in the stronger cores, enough to
solidify the SLGT risk forecast.

...Mid Atlantic...

The period can be characterized by uncertainty within the guidance
as a disheveled surface and mid-level reflection left over from
what was Potential Tropical Cyclone 8 (PTC8) continues to meander
over the Mid Atlantic with a broad PWAT anomaly positioned across
Northern NC through the Delmarva. The interesting aspect of the
forecast is multiple deterministic outputs have some prospects of
heavy rainfall across parts of the Mid Atlantic, but there is a
large disagreement on where exactly that could take place. The
issue is the lack of an organized surface reflection that can help
bring everything together, but still has a presence that can allow
for smaller zones of opportunity to crop up. Assessing the ensemble
QPF has helped curb some of the discontinuity within the
deterministic leading to two areas of focus within the next 24 hrs.

The first is across the coast of NJ where an axis of convective
potential seems reasonable as the weak surface low analyzed over
Eastern NC begins to drift northeast with some resemblance of
organization as it enters over the Gulf stream. A modest jet streak
is forecast to develop over the Western Atlantic with the surface
low likely to lie within the left exit region of the jet allowing
for some modest strengthening as it moves northeast off the coast
of DE/NJ. The synoptic evolution is moving towards the "classic"
axis of deformation prospects as the low begins to intensify and
the western side of the cyclone exhibits a band of heavier precip
close to the DE/NJ coastal plain. This was outlined within the
latest HREF ensemble blended mean QPF with the matched mean QPF
displaying a relatively significant heavy QPF signature within the
Southern and Central NJ coast impacting areas from just north of
Cape May up through Atlantic City to just to the east of Toms
River. These areas aren't as flood prone compared to some of the
focused urban corridors inland, but the combination of some heavy
surf with rainfall rates between 1-2"/hr could cause some localized
flooding within the coast. Considering some of the uncertainty, the
only risk to add was a MRGL as the probabilities for >3" and >5" are
still favorable (40-60% and 15-30% respectively), but with only
modest agreement amongst guidance, it would be hard to issue
anything higher.

The second area of interest lies within much of Northern and
Eastern VA where the closed 500mb low will continue to spin south
of the region prompting some weak ascent focused over a region of
relatively modest instability and deep layer moisture. This is
another scenario where the guidance has precip, but the focus is
anywhere from Southern PA down to Hampton, VA. HREF probabilities
signal a broad axis of 40-60% probs for >3" somewhere from the WV
Panhandle down to Virginia Beach with some low end >5" probs
lingering within the same corridor. Ensemble QPF footprint depicts
an areal average of 1-1.5" located across the above zone with a
maxima centered over Northern VA. The prospects for heavy rainfall
also include areas along the Potomac, including the DC metro which
has notoriously lower FFGs thanks to urban sprawl. There is too
much uncertainty again for anything more than a MRGL risk, however
the environment is favorable for somewhere to see a heavy cell or
two that could cause issues. For that, have opted to add a second
MRGL risk within the Mid Atlantic with points between the two risk
areas void from the threats due to a greater model consensus
pointing at a relative QPF min within that area of the Delmarva.

...North-Central Sierra and Western NV...

Another broad closed upper low will come ashore over Northern CA
from the Pacific leading to increased moisture and favorable upper
forcing across the terrain of CA/NV beginning later this afternoon.
Despite cooler surface temps, steep low and mid-level lapse rates
with a decent outline of positive buoyancy within the forecast
soundings out of KREV signal the potential for some heavier
convective cell initiations across the North-Central Sierra over
into Western NV. There has been an uptick in the ensemble QPF
across this area the past succession of runs leading to a bit more
potential than what was thought prior. Historically, including with
the past system, we've seen these strong upper lows tend to
overachieve at times with the magnitude and spatial coverage of the
convection downstream. In this case, it's favoring the prospects
for locally heavy rainfall in the complex terrain and over an area
of lower FFGs like Reno which carry the urbanization factor. The
latest UFVS First Guess Field has also introduced a recommended
MRGL risk for the first time in its runs as of late with the uptick
in the signal. A MRGL risk was added to account for the threat with
the threshold still on the lower half of the risk spectrum.

Kleebauer


Day 2
Valid 12Z Thu Sep 19 2024 - 12Z Fri Sep 20 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

A non-zero flash flood threat does exist across portions of the
Upper Midwest, however the antecedent dry conditions will allow for
much of this rain to be beneficial over the area of interest
(Northern IA, Southeastern MN, Western WI, and the Arrowhead of
MN). Urban corridors will be the most favorable spots for flash
flood prospects. Rates generally capped around 1-2"/hr, falling shy
of the current FFG forecast in the area. If the signal becomes more
impressive in the next 24 hours, a targeted MRGL is possible.

Kleebauer


Day 3
Valid 12Z Fri Sep 20 2024 - 12Z Sat Sep 21 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer
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FOUS30 KWBC 190742
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
342 AM EDT Thu Sep 19 2024

Day 1
Valid 12Z Thu Sep 19 2024 - 12Z Fri Sep 20 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE TRANSVERSE RANGES OF CALIFORNIA, UPPER MIDWEST, AND THE URBAN
CORRIDOR OF SOUTHEAST FLORIDA...

...California...

A fairly stout closed upper low over the Pacific will be the
driving force behind increased forcing and region moisture
advection into the southern half of California this period. Recent
wildfires have brought about a plethora of burn scars within the
terrain of the Transverse Ranges that have become increasingly
susceptible to flash flooding prospects due to hydrophobic soils
allowing for consistent run off capabilities. The pattern evolution
supports a strong mid and upper forcing regime to be co-located
within the Central and Southern CA coasts, as well as the immediate
terrain to the east of the coastal plain. Latest 00z HREF mean QPF
distribution pinpoints a regional maxima within the confines of
the Transverse Range, intersecting an area with multiple burn scar
locations that will likely exhibit flash flood effects thanks to
the current antecedent soil environment. There's a consensus within
both the mean QPF and probability fields for >1" of rainfall in-of
the aforementioned area with even some prospects for locally >2"
as noted within the neighborhood probabilities for D1. With
coordination from earlier updates by the local WFOs involved
prompting the MRGL risk, and with the signal remaining prolific
enough from the latest guidance, the MRGL risk was maintained to
project continuity.

...Upper Midwest...

An increasingly favorable pattern will invoke a period of
scattered to widespread thunderstorm activity capable of producing
locally enhanced rainfall cores leading to 1-2"/hr rain rates in
the strongest convective cores. Steepening lapse rates, increasing
bulk shear, and modest surface to mid-level buoyancy will create an
environment conducive for not only thunderstorm initiation, but
prolonged updrafts capable of maintaining significant storm
structure within a core of elevated PWATs advected ahead of a mean
trough to the west. Latest HREF EAS signals for >1" are pretty high
(60-80%) across much of Northwest WI, an area where most CAMs are
pinpointing as the primary area of focus for this afternoon's and
evening's convective prospects. Neighborhood probs are a bit less
emphatic than what normally constitutes a higher impact potential,
but still fairly significant nonetheless for potential totals
ranging between 2-4" over portions of Eastern MN into Northwest WI.
The antecedent conditions present within the zone of highest
probabilities is borderline unfavorable for flooding with NASA
SPoRT indicating soil moisture percentiles closer to 40-50% over
the area. Considering the favorable environment and SPC outlining
the area with a Slight Risk for severe weather, believe the setup
is good enough for a targeted MRGL within the core of the best
probabilities based off the latest hi-res ensemble.

...Southeast Florida...

A meandering frontal boundary in-of South FL will become a focal
point for elevated convective coverage, especially just inland of
the urban metro of Miami up to West Palm Beach when sea breeze
initiation becomes tied within the frontal positioning later this
afternoon. The steering pattern is favorable for convective
development to drift back over the urban metro, settling within a
modest PWAT anomaly situated over the area. The core of convection
will likely drop rates between 1-3"/hr with intra-hour rates >3"
more than plausible, a factor that typically causes flash flood
concerns within the urban corridor. HREF blended mean QPF has a
bullseye situated within the Fort Lauderdale/Pompano Beach area
with a small secondary max near Miami. This signal is fairly
classic for a lower category risk, especially when you add the
steering pattern leading to favorable motions back over the cities
along the Southeast FL coast. The previous forecast was maintained
with only a very minor adjustment along the western periphery of
the risk area.

Kleebauer


Day 2
Valid 12Z Fri Sep 20 2024 - 12Z Sat Sep 21 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE URBAN CORRIDOR OF SOUTHEAST FLORIDA, NORTHEAST NEW MEXICO, AND
THE DESERT SOUTHWEST...

...Southeast Florida...

A secondary period of impact from active sea breeze convection and
propagation into the urban corridor is forecast to transpire on
Friday afternoon. The signal is not as robust as the previous
period, but any heavy rainfall prior would precede this potential
event with lower FFG signals leading to a bit more sensitivity to
flash flood prospects. The ensemble mean QPF is a touch less
aggressive as stated, so it will remain a period to monitor to see
if the threat trends higher once we move closer to the range of the
CAMs. For now, maintained general continuity as the signal
persists for a flash flood threat in-of the urban corridor
extending from Miami up through West Palm Beach.

...New Mexico...

The prolific closed upper circulation out across the Southwest will
begin pressing eastward with an increased upper forcing pattern
thanks to a broad diffluent axis downstream of the mean
trough/upper low. Most of the latest global deterministic eject a
rapidly moving shortwave out of Chihuahua, traversing over the
Eastern half of NM by the afternoon and evening hours Friday. A
tongue of modest instability based off the mean MUCAPE forecast
from all the deterministic is forecast to bisect that eastern side
of the state with the best focus aligned from the Sacramentos up
through the western side of the Caprock and into the High Plains of Northeastern NM. Flash flooding threats will likely be tied to
urban areas and some of the remnant burn scars located within the
Sacramento Mountains, however these setups are notoriously tricky,
especially with the propensity for convection to become anchored
along the instability gradient favored in the terrain and adjacent
Caprock. Some of the deterministic output is pretty reasonable for
isolated flash flood prospects, especially when you add the
increasingly favorable upper pattern. A small MRGL risk was added
to encompass the areas above with the threat lying on the lower-end
of the risk threshold.

...Desert Southwest...

Our deep closed upper reflection will migrate slowly to the east
with the circulation likely crossing Southern CA into the interior
Desert Southwest as we move towards the end of the period. As of
now, the current QPF output is not exactly what would constitute a
favorable flash flood scenario. However, considering the expected
pattern evolution and the advection of more moist, buoyant air
northward ahead of the upper low, you have to acknowledge the
prospects of a more scattered pulse convective pattern over an
area that is much more conducive for flash flood potential. Recent
ECMWF AIFS ML output was actually more aggressive than the recent
deterministic in the spatial coverage of precip, and even for the
magnitude of the expected setup. This tends to signal a red flag
for the deterministic not being aggressive enough with such a
strong mid and upper pattern. A low-end MRGL was placed over
portions of Southern CA/NV into Western AZ to outline the favored
area for scattered convective development with modest storm cores
capable of locally heavy rainfall.

Kleebauer
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FOUS30 KWBC 200821
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
421 AM EDT Fri Sep 20 2024

Day 1
Valid 12Z Fri Sep 20 2024 - 12Z Sat Sep 21 2024

......THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN UNITED STATES......

...Southern California/Western Arizona Deserts...

An upper low moving down the coast early today will move inland over
the Desert Southwest later today. Increasing coverage of showers
and thunderstorms are expected as moisture will accompany the low
into the usually dry areas of southeast California, southern Nevada,
and northwestern Arizona..with greatest coverage tied to the
steepest low- to mid-level lapse rates at the center of the upper
low where upper level temperatures will be coldest. That is also
where steering flow becomes weak...leading to slow moving storms.
With any more persistent showers and storms, expect isolated flash
flooding with any burn scars, dry washes, and other flood-prone
areas.PWATs between 0.5 and 0.75 inches in these areas will peak at
about 1.5 sigma above normal for this time of year.

...New Mexico...

Broad upper level diffluence ahead of the positively tilted low
over the Desert Southwest will cause a somewhat narrow 50-100 mile
wide plume of training showers and possibly embedded thunderstorms
to develop over eastern New Mexico and into portions of the far
western Texas and Oklahoma Panhandles. Given the sensitivities of
some of these areas to prolonged rainfall, the Marginal risk
remains in place, especially for any burn scars or flood prone
areas.

...South Florida...

Today looks to be the final day of heavy rainfall potential is
expected in South Florida...especially in the urban corridor from
West Palm Beach south through Homestead. Highly efficient rainfall
producing thunderstorms should be slow-moving on the leading edge of
an advancing cold front. The front will clear South Florida by
early Saturday turning the predominant flow more northeasterly. This
will cut down on the precipitable water values some, while also
greatly limiting, though not eliminating the coverage of storms by
Saturday. Thus, the Marginal flash flooding threat should end once
the convection simmers down late this afternoon or this evening.

Bann


Day 2
Valid 12Z Sat Sep 21 2024 - 12Z Sun Sep 22 2024

......THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF
THE CENTRAL ROCKIES AND CENTRAL PLAINS......

A broad upper trough with evolution of a closed low over the West
will translate eastward on Saturday with an evolving setup capable
of showers and thunderstorms across the Rockies through the
Central Plains, especially once the trough axis picks up forward
speed. A combination of favorable ascent and increased moisture
advection thanks to a developing LLJ pattern east of the Front
Range will lead to thunderstorms capable of producing several
heavy cores with locally enhanced rainfall. The 20/00Z HREF
neighborhood probabilities...available only during the first half
of the day 2 outlook period on the overnight shift...focuses brief
periods of 30 percent or greater probabilities of exceeding 1 inch
per hour developing out over the plains of eastern New Mexico that
ease into West Texas by early evening...with the threat continuing
into Saturday night in response to the development of a low level
jet. Farther north...the signals for locally heavy rainfall also
appear across portions of the Plains states as thunderstorms form
along and ahead of a cold front tied to an amplifying upper trough
building across the northern US. As mentioned in a previous discussion...antecedent conditions and the fact that much of the
area is rural will help mitigate some of the flash flooding concern
due to amount of infiltration possible.

Bann


Day 3
Valid 12Z Sun Sep 22 2024 - 12Z Mon Sep 23 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE SOUTHERN
GREAT LAKES SOUTHWESTWARD ACROSS PORTIONS OF THE CENTRAL PLAINS...

An upper trough initially over the central and southern Rockies on
Sunday morning will move eastward on Sunday into early Monday
morning...with showers and thunderstorms developing ahead of the
front in an airmass characterized by precipitable water values
generally in the 1.6 to 1.8 inch range. Given the moisture in place
and enough mid- and upper-level shear to support some convective organization...the possibility exists for excessive rainfall due to
some intense downpours. Tended to favor the cluster of models
guidance led by the ECMWF/GFS/CMC with respect to the potential for
heaviest amounts somewhere from southeast Kansas into
Missouri...but did not go as far east as suggested by the
aggressive UKMET. Suspect there is a non-zero threat of excessive
rainfall farther to the southwest where storms may also be able to
organize but for now favored the better moisture and the region of
better upper difluence.

Bann
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FOUS30 KWBC 210835
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
435 AM EDT Sat Sep 21 2024

Day 1
Valid 12Z Sat Sep 21 2024 - 12Z Sun Sep 22 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN HIGH PLAINS...

...New Mexico into Texas/Oklahoma Panhandles...
The large-scale flow across the southern Great Basin will continue
to draw moisture northward at the low levels while becoming increasingly diffluent aloft in response to the approach of an upper low moving
across the southern Great Basin today. Precipitable water values
are forecast to exceed 1.5 inches across parts of West Texas by
late afternoon while the right entrance region of an upper level
jet rounds the base of an upper trough and tracks over the region.
This combination should help support multi-cell storms capable of
producing isolated rainfall rates of an inch or more and storms
total rainfall amounts in excess of 2 inches over portions of
northeastern New Mexico into the Texas panhandle during the
afternoon or evening hours with an associated risk of flash
flooding. There was one round of showers and thunderstorms
that developed on Friday evening over southeast Kansas and
weakened as it moved into southwest Missouri...followed by a second
flare up of convection in the overnight hours on a track a bit to
the south of the first round. There was some concern is more about
the cumulative effect of multiple rounds lowering the flash flood
guidance here ahead of anything developing later in the day...but
warming cloud tops and limited coverage of 1 inch amounts was
enough to keep the area in the Marginal risk category for the time
being.

Bann


Day 2
Valid 12Z Sun Sep 22 2024 - 12Z Mon Sep 23 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID MISSISSIPPI VALLEY TO THE SOUTHERN HIGH PLAINS...

The focus for areas of heavy rainfall will continue to be along a
plume of deeper moisture...precipitable water values generally at
or above 1,75 inches...from the western portion of Texas
northeastward to where it begins to encounter a cold front moving
in from the northern United States. An upper level shortwave trough
over the central and southern Rockies on Sunday morning will eject
eastward during the day...aiding the formation of storms over parts
of western Texas capable of heavy downpours around the time of
maximum heating. Farther to the east...model guidance tends to
generate at least some convection capable of producing isolated 2
to 3 inch rainfall amounts over portions of Missouri as moisture
flux convergence occurs ahead of a cold front pushing southward.
Mesoscale guidance...available through the first 12 hours of the
Day 2 period for the overnight EROs...does show low-end potential
for 2 inch per hour rates embedded within a broader area where
probabilities of 1 inch per hour rates are on the order of 10 to 25
pct. There was already a Slight Risk introduced here and only
needed a bit of realignment to fit the latest guidance.

Bann


Day 3
Valid 12Z Mon Sep 23 2024 - 12Z Tue Sep 24 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A PORTION OF
THE MISSISSIPPI VALLEY EASTWARD INTO THE OHIO VALLEY...

As the large scale upper trough continues to move eastward on
Monday...the plume of available moisture gets elongated and the
moisture flux along the front becomes less well defined. There will
be some broader upper support along the front which will have taken
on a more east-west orientation...so there is at least some
potential for problems from run off with 1 to 2 inches or rainfall
over portions of Illinois into Indiana. But with convection
expected to become increasingly elevated and with flash flood
guidance tending to be 2.5 inches per hour or greater...will
maintain a Marginal Risk area for now and evaluate the need for an
upgrade if rates/amounts pick up in later model cycles.

Bann
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FOUS30 KWBC 220834
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
434 AM EDT Sun Sep 22 2024

Day 1
Valid 12Z Sun Sep 22 2024 - 12Z Mon Sep 23 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID MISSISSIPPI VALLEY TO THE SOUTHERN HIGH PLAINS...

The focus for areas of heavy rainfall will continue to be within a
plume of deeper moisture ahead of a large-scale upper trough making
its way out over the plains towards the Mid-Mississippi Valley. The
airmass already in place had precipitable water values generally
at or above 1,75 inches...from the western portion of Texas
northeastward to where it encounters a cold front moving in from
the northern United States. Latest model runs still support two
areas of more concentrated rainfall warranting a Slight Risk area--
namely over western Texas and from southern Missouri into southern
Illinois. The southern area should be more driven by diurnal
instability strong enough to support spotty 2 or 3 inch rainfall
amounts and rainfall rates topping an inch per hour. The area
farther east will have the added advantage of a surface front to
help focus moisture convergence but the upper support is not
expected to be as strong as it was on Saturday. For that
reason...confidence in occurrence is somewhat diminished. Made a
small southward adjustment to the Slight Risk area based on latest
guidance and a trimmed a bit of the northern periphery of the
Marginal given the placement of the cold front.

Bann


Day 2
Valid 12Z Mon Sep 23 2024 - 12Z Tue Sep 24 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID MISSISSIPPI VALLEY...

Surface low pressure begins to develop on Monday as shortwave
energy moving through the southern stream trough...leading to
renewed showers and thunderstorms in the Mid-Mississippi Valley
early in the day that shifts into the Ohio Valley by late Monday
night/early Tuesday morning. The best overlap of ingredients and
forcing looks appears to be from the afternoon into the early
evening across portions of southeast Missouri into parts of
southern Illinois. After that...low level flow should take on an
increasing component parallel to the front. Between the weakening
magnitude of moisture flux convergence at the front and the loss of
daytime heating/destabilization...rainfall rates should be waning.
There are a few ensemble members which generate over an inch of
rain over the Ohio Valley as upper flow backs in response to energy
in the northern stream...but the expectation is that the flash
flooding risk is minimal with those rainfall rates and dry
antecedent conditions.

Bann


Day 3
Valid 12Z Tue Sep 24 2024 - 12Z Wed Sep 25 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE Eastern OHIO VALLEY AND ACROSS CENTRAL OF WESTERN TEXAS...

Ohio Valley...
As energy in the southern stream interacts with digging energy in
the northern stream late on Day2...the flow begins to back and
become diffluent leading to increasing coverage of rainfall by the
time Day 3 begins. The flow should continue to become increasingly
diffluent aloft with precipitable water values now about 1.75
inches in place. Spaghetti plots of QPF from the ensembles show
minimal support for amounts greater than 2 inches...and most of
that support is from just a few GEFS members. With antecedent
conditions being so dry...it is presumed that only isolated
instances will occur that run off problems occur.

Texas
Light southeasterly on-shore flow across far southern Texas will
start to draw moisture northward again on Tuesday afternoon. As it
does so..a weakening cold front will help provide some focus for
showers and a few thunderstorms in central or western Texas. The
NAM and ECMWF were the only two operational runs from the 22/00Z
model suite to generate 2+ inch amounts of QPF while the GFS had
support from the GEFS favoring a weaker/drier solution. Given the uncertainty...opted to maintain a Marginal risk for this cycle.

Bann
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FOUS30 KWBC 230815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Mon Sep 23 2024

Day 1
Valid 12Z Mon Sep 23 2024 - 12Z Tue Sep 24 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID-MISSISSIPPI VALLEY EASTWARD TO THE SOUTHERN APPALACHIANS...

Precipitation over the southern Plains will continue to spread
north ahead of a positively-tilted upper shortwave trough drifting
east through the central Plains. Deepening moisture (PWs ~1.75-2
inches) supported by southwesterly inflow, and large-scale ascent
generated by the upper shortwave, are expected to produce a broad
area of precipitation spreading northeast early in the period from
the Ozarks through the lower Missouri and mid Mississippi valleys.
There is the potential for a stripe of locally heavy amounts, with
the 00Z HREF showing high neighborhood probabilities for
accumulations of 3 inches or more from central Missouri eastward
through the St. Louis metro. However, limited instability should
help to keep rainfall rates in check through the morning hours. A
better chance for heavy rainfall rates may develop later in the day
as trailing energy and daytime heating contribute to storms
redeveloping near the Ozarks and tracking northeast through the mid
Mississippi Valley and into the lower Ohio Valley later this
afternoon into the evening.

Moisture spreading further east is expected to fuel showers and
storms developing later today across the central and southern
Appalachians. Some of the hi-res guidance continue to show some
potential for isolated heavy amounts across the region, with the
greatest threat centered over western North Carolina, where the
HREF is showing high neighborhood probabilities for accumulations
of 2 inches or more.

Pereira


Day 2
Valid 12Z Tue Sep 24 2024 - 12Z Wed Sep 25 2024

..THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE OHIO VALLEY AND THE CENTRAL TO SOUTHERN APPALACHIANS...

The shortwave trough moving across the mid Mississippi Valley on
Day 1 will begin to interact with a northern stream trough
amplifying over the northern Plains early in the period. Models
show the upper pattern quickly amplifying over the Mississippi
Valley on Tuesday. At the surface, low pressure is expected to
track northeast from the mid Mississippi Valley to the Great Lakes,
with a trailing cold front extending back through the Ohio Valley.
An axis of deeper moisture (PWs ~1.50-1.75 inches) coinciding with
deep southeasterly flow ahead of the upper trough will fuel
showers and storms along the low track and ahead of the trailing
cold front. Models do not present a signal for widespread heavy
amounts but show the potential for locally heavy amounts,
including for portions of the central to southern Appalachians,
where relative soil moisture is slightly higher and flash flood
guidance values lower.

Pereira


Day 3
Valid 12Z Wed Sep 25 2024 - 12Z Thu Sep 26 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST, TENNESSEE VALLEY, AND THE SOUTHERN APPALACHIANS...

Although disagreements on the track continue, the consensus of the
models show a powerful tropical cyclone tracking north through the
eastern Gulf of Mexico during this period. Apart from the faster
Canadian solutions, which bring heavy amounts into the Florida
Panhandle, most of the deterministic models and their ensemble
means show moderate to heavy rains brushing the coast, but the
heaviest amounts remaining out over the open waters through 12Z
Thu. Therefore, just a Marginal was maintained from South Florida
and the Keys northward along the Florida Gulf Coast through the
Panhandle. However, should more guidance begin to trend toward a
faster solution, future upgrades may be necessary.

Despite their disagreements with the cyclone track, the models are
presenting a growing signal for heavy amounts developing well to
the north. The cold front pushing east into the Ohio, Tennessee,
and lower Mississippi Valley prior to the period is forecast to
slow across the region, providing a focus for moisture ushered in
by strong southeasterly to easterly flow ahead of the system. With
some longitudinal disagreement, the GFS and ECMWF show PWs
increasing to 1.75-2 inches along an axis of strong low level
convergence extending north from the northern Gulf Coast into the
Tennessee Valley. Meanwhile, an upper low that will begin to
develop over the mid Mississippi Valley on Wednesday is expected to
drop south, enhancing lift across the region. While there is some
west-east disagreement on its placement, most of the 00Z
deterministic runs showed a stripe of 2-4 inch accumulations
extending northeastward from northern Alabama into the southern
Appalachians.

Pereira
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FOUS30 KWBC 240826
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
426 AM EDT Tue Sep 24 2024

Day 1
Valid 12Z Tue Sep 24 2024 - 12Z Wed Sep 25 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE OHIO/Tennessee VALLEYS AND ADJACENT PORTIONS OF THE MID-ATLANTIC ...

One area of showers and thunderstorms that produced spotty moderate
to heavy rainfall overnight along a quasi-stationary front
overnight should be weakening as it reaches portions of the Mid-
Atlantic region by morning. However...shortwave energy in the
northern stream will be developing a closed low that deepens with
time as it tracks from the Upper Midwest into the Mid-Mississippi
Valley later tonight. This backs the flow aloft and supports some
convection with locally heavy rainfall rates in a diffluent flow
regime over the eastern Ohio Valley as well as thunderstorms ahead
of the low track and ahead of a trailing cold front. Model guidance
continues to show the potential for locally heavy amounts while not
presenting a signal for widespread heavy rainfall
totals...including portions of the central and southern
Appalachians where relative soil moisture is slightly higher and
where flash flood guidance was lower.

Bann


Day 2
Valid 12Z Wed Sep 25 2024 - 12Z Thu Sep 26 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST UNITED STATES AND EASTERN TENNESSEE VALLEY...

Only minor adjustments were needed to the previously issued Slight
risk area from portions of Alabama and Georgia into southeast
Tennessee...while a targeted Slight Risk area was introduced along
the coastline of the Florida panhandle. It appears that a
predecessor rainfall event will take shape somewhere in the
Southeast US as moisture streams northward from the Gulf of Mexico
ahead of Potential Tropical Cyclone Nine and interacts with a cold
front dropping southward from the Tennessee Valley. There is still
some disagreement among the various models with respect to where
the axis may set up but the area covered by the Slight risk has the
best overlap of different solutions so only minor adjustments were
needed to what is effectively a high-end Slight Risk area. Along
the coast...model QPF has increased along portions of the Florida
coastline to the point where a Slight seems warranted.

Bann


Day 3
Valid 12Z Thu Sep 26 2024 - 12Z Fri Sep 27 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST UNITED STATES AT POTENTIAL TROPICAL CYCLONE NINE
MOVES INLAND...

There should be an increasing threat of widespread and potentially
significant rainfall as Potential Tropical Cyclone Nine approaches
the coast and eventually makes landfall sometime around 27/00Z
based on the latest guidance from the National Hurricane Center.
Moderate to heavy rainfall may develop across portions of Florida
panhandle into the Southeast US well before PTC Nine make landfall
as strong transport of Gulf moisture interacts with deepening mid-
and upper-layer closed low over the central/southern Mississippi
Valley. Primary changes were to extend the Moderate risk area
northward along the NHC path of PTC Nine where the guidance had
shown an increase in rainfall amounts...with the Moderate risk now
into the southern Appalachians where terrain effects look to result
in locally enhanced rainfall amounts.

With an unusually deep low best seen in the mid- and upper-levels
located to the west...at least some of the moisture being drawn
inland by Nine will begin to get drawn westward over portions of
the Tennessee Valley and into the Mississippi Valley. As a
result...part of the Slight risk area from the Southeast US gets
pulled westward into the Tennessee Valley around the mid- and
upper-level low. Given the model spread and the poor run to run consistency...refrained from taking the Slight risk area too far
westward at this point.

Bann
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FOUS30 KWBC 241659
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1259 PM EDT Tue Sep 24 2024

Day 1
Valid 16Z Tue Sep 24 2024 - 12Z Wed Sep 25 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE VIRGINIA/NORTH CAROLINA PIEDMONT NEAR THE STATE LINE...

...16Z Update...

...VA/NC border...

In coordination with RNK/Blacksburg, VA; RAH/Raleigh, NC; and
AKQ/Wakefield, VA forecast offices, a Slight Risk area was
introduced with this update along the VA/NC border in the Piedmont
area. Tonight, much of the guidance, including the 12Z HRRR, HREF,
and both ARWs are suggesting an area of training convection will
develop. The heavy rain will be forced by a stationary surface
trough over the area combined with a local maximum of atmospheric
moisture with PWATs over 1.75 inches. A strong and deep upper level
trough over the Mississippi Valley will greatly increase the upper
level divergence to its east. This too will greatly add lifting
support to the storms as they form with the convective maximum
after sunset this evening. HREF probabilities are up to 30% of
exceeding FFGs in the western part of the Slight risk area, as well
as over 80% of exceeding 3 inches of rain in the neighborhood
probabilities and almost 50% of exceeding 5 inches through
tonight.

The factors working against heavy rain and flash flooding are some
antecedent dry conditions, with at least average soil moisture
across this area, and marginal instability generally around 500 to
1,000 J/kg. The instability will limit to some extent the
widespread coverage of the heavy rain, but the excellent forcing
may be able to make up for that. Portions of the Slight Risk area
saw heavy rainfall last week, which at least has kept those area
from having totally dry soils...but average soil moisture can
sometimes work against flash flooding as some clays can be
hydrophobic when they're really dry, resulting in extra runoff.
Such is not expected to be the case here.

...Midwest...

Elsewhere across the Upper Ohio and Tennessee Valleys expect
continued off and on showers and storms, but general struggles with organization. Very dry soils north of the Ohio River should also
generally limit the flooding threat...whereas along the west facing
slopes of the Appalachians, localized upslope may enhance it a bit.
Regardless any flash flooding in these areas should be confined to
urban and flood-prone locations.

Wegman

...Previous Discussion...

One area of showers and thunderstorms that produced spotty moderate
to heavy rainfall overnight along a quasi-stationary front
overnight should be weakening as it reaches portions of the Mid-
Atlantic region by morning. However...shortwave energy in the
northern stream will be developing a closed low that deepens with
time as it tracks from the Upper Midwest into the Mid-Mississippi
Valley later tonight. This backs the flow aloft and supports some
convection with locally heavy rainfall rates in a diffluent flow
regime over the eastern Ohio Valley as well as thunderstorms ahead
of the low track and ahead of a trailing cold front. Model guidance
continues to show the potential for locally heavy amounts while not
presenting a signal for widespread heavy rainfall
totals...including portions of the central and southern
Appalachians where relative soil moisture is slightly higher and
where flash flood guidance was lower.

Bann


Day 2
Valid 12Z Wed Sep 25 2024 - 12Z Thu Sep 26 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST UNITED STATES AND EASTERN TENNESSEE VALLEY...

Only minor adjustments were needed to the previously issued Slight
risk area from portions of Alabama and Georgia into southeast
Tennessee...while a targeted Slight Risk area was introduced along
the coastline of the Florida panhandle. It appears that a
predecessor rainfall event will take shape somewhere in the
Southeast US as moisture streams northward from the Gulf of Mexico
ahead of Potential Tropical Cyclone Nine and interacts with a cold
front dropping southward from the Tennessee Valley. There is still
some disagreement among the various models with respect to where
the axis may set up but the area covered by the Slight risk has the
best overlap of different solutions so only minor adjustments were
needed to what is effectively a high-end Slight Risk area. Along
the coast...model QPF has increased along portions of the Florida
coastline to the point where a Slight seems warranted.

Bann

Day 3
Valid 12Z Thu Sep 26 2024 - 12Z Fri Sep 27 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHEAST UNITED STATES AT POTENTIAL TROPICAL CYCLONE NINE
MOVES INLAND...

There should be an increasing threat of widespread and potentially
significant rainfall as Potential Tropical Cyclone Nine approaches
the coast and eventually makes landfall sometime around 27/00Z
based on the latest guidance from the National Hurricane Center.
Moderate to heavy rainfall may develop across portions of Florida
panhandle into the Southeast US well before PTC Nine make landfall
as strong transport of Gulf moisture interacts with deepening mid-
and upper-layer closed low over the central/southern Mississippi
Valley. Primary changes were to extend the Moderate risk area
northward along the NHC path of PTC Nine where the guidance had
shown an increase in rainfall amounts...with the Moderate risk now
into the southern Appalachians where terrain effects look to result
in locally enhanced rainfall amounts.

With an unusually deep low best seen in the mid- and upper-levels
located to the west...at least some of the moisture being drawn
inland by Nine will begin to get drawn westward over portions of
the Tennessee Valley and into the Mississippi Valley. As a
result...part of the Slight risk area from the Southeast US gets
pulled westward into the Tennessee Valley around the mid- and
upper-level low. Given the model spread and the poor run to run consistency...refrained from taking the Slight risk area too far
westward at this point.

Bann
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FOUS30 KWBC 250903
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
503 AM EDT Wed Sep 25 2024

Day 1
Valid 12Z Wed Sep 25 2024 - 12Z Thu Sep 26 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST UNITED STATES...

Even though Helene should still be well off-shore during the
period...abundant moisture should be streaming northward ahead of
the storm. The models have been increasingly aggressive with
rainfall amounts coming off the Gulf into the Florida panhandle
with locally excessive amounts of rainfall along the coastline. Of
greater concern is the moisture that continues to stream northward
into portions of northern Georgia and upstate South Carolina where
a surface cold front acts to focus a predecessor rainfall event.
Some pieces of guidance...including the HAFS A and B parent grids
...drop 5 or 6 inches or rainfall within a broader area of 2 to 4
inches of rainfall. The overall agreement on placement of the axis
is really very good with only subtle east/west variations...which
necessitated an expansion of the moderate risk area and now
includes some of the complex terrain of the southern Appalachians.
Slight and Marginal risk areas surrounding covered the risk of
convection forming along broad synoptic scale flow getting drawn
into the environment ahead of Helene.

Bann


Day 2
Valid 12Z Thu Sep 26 2024 - 12Z Fri Sep 27 2024

...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL IN PORTIONS OF THE
SOUTHERN APPALACHIANS...

Given the increasing confidence about the overlap of the axis of
a predecessor rainfall event on Day 1 period and the amount of
rainfall expected as the center of Helene approaches the southern
Appalachians during the latter part of the Day 2 period...there has
been a growing number of models generating close to 10 or 11
inches of rainfall for the 2-days combined in the complex terrain.
That raises concerns about impactful flooding becoming widespread
with considerable and potentially life-threatening flash and urban
flooding as well as areas of significant river flooding over
portions of Florida, the Southeast U.S. and the southern
Appalachians. Widespread minor to moderate river flooding is likely
and major river flooding is possible. Landslides are possible in
areas of steep terrain in the southern Appalachians given these
rainfall amounts. This prompted the upgrade to a high risk over
portions of northwestern Georgia into far western South Carolina
that was mainly confined to the terrain. What effectively amounts
to a high-end moderate risk surrounds the high that extends along
much of the track as Helene makes landfall along the Florida
panhandle coastline around 27/00Z (give or take a couple of hours)
based on the latest NHC guidance. In terms of model guidance...the
tracks tended to be clustered well resulting in NHC guidance being
close to most model runs. For the Day 2 period...that resulted in
the highest rainfall totals being close to each other where the
orographic forcing was consistent. A second axis of excessive
rainfall branched off to the northwest from Helene's track towards
a deep-layered low developing over the southern portion of the
Mississippi Valley as moisture gets entrained into that system
leading to scattered convection that could produce locally heavy
amounts. Mainly confined the Slight risk to the Tennessee Valley
and only a Marginal risk extending back towards the core of the
upper system.

Bann


Day 3
Valid 12Z Fri Sep 27 2024 - 12Z Sat Sep 28 2024

...INTRODUCED A MODERATE RISK OF EXCESSIVE RAINFALL OVER A PORTION
OF THE UPSLOPE REGION INTO THE SOUTHERN APPALACHIANS...

Based on latest NHC track guidance...Helene should be in northern
Georgia and tracking on a more northwestward course during the day.
This suggests the flow of deep moisture should be on-going to the
terrain of western Carolinas into southwest Virginia. Latest model
guidance shows several inches of rainfall in addition to what falls
in the predecessor 48 hours...felt a focused Moderate risk placed
where there was best model consensus was warranted. It was also a
multi-day rainfall total farther south along the NHC track in the
eastern Tennessee Valley that was the main reason to keep a Slight
Risk where model QPF be a little too light to support one. That
portion of the Slight Risk area extends westward to the deep-
layered low where steepening low level lapse rate and the
additional moisture streaming off of Helene could lead to some
showers and thunderstorms capable of producing locally heavy
downpours.


Bann
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FOUS30 KWBC 280758
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
358 AM EDT Sat Sep 28 2024

Day 1
Valid 12Z Sat Sep 28 2024 - 12Z Sun Sep 29 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
OHIO AND TENNESSEE VALLEYS AS WELL AS FOR CENTRAL FLORIDA...

...Ohio/Tennessee Valleys...

The combined upper low and remnant circulation of what is left of
Helene is expected to slow/stall over the Ohio and Tennessee
Valleys. With very little if any instability to work with the bulk
of rain today will likely be stratiform with hourly rates around
0.5 inch/hour or lower. At best there may be some isolated flash
flooding, therefore maintained the broad Marginal Risk that is in
place over the region.

...Florida...

A trailing cold front across the Florida peninsula will be present
during this period along with abundant instability and moisture
within proximity to this feature. The development of strong
thunderstorms can be expected, especially on the western side of
the peninsula. Recent heavy rain has increased soil sensitivity for
much of the area therefore maintained a Marginal Risk for excessive
rainfall for the western and central peninsula.

Campbell


Day 2 Valid 12Z Sun Sep 29 2024 - 12Z Mon Sep 30 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC/APPALACHIANS AS WELL AS THE NORTHERN FLORIDA
PENINSULA...

...Mid-Atlantic/Central Appalachians...

During this period the remnant low of Helene will get picked up by
the upper level jet and track eastward into the Mid-Atlantic and Central/Northern Appalachians. There will be an increase in
available instability which may lead to localized enhanced rainfall
rates for portions of the Shenandoah Valley and west to the
Allegheny Front in Maryland, West Virginia, and Virginia; which may
result in isolated to widely scattered instances of flash
flooding. The level of threat continues to be handled well with the
Marginal Risk that is currently in effect. There may be a need for
a Slight Risk with future updates depending on model trends and
observations.

...Florida...

Convection will continue to fire up in proximity to a stalled
frontal boundary draped across northern/central Florida. Storm
motion may be fast-moving with some tracking over areas hard-hit
by Helene, but because progressive nature of the convection a
Marginal Risk remains appropriate for this period.

Campbell


Day 3
Valid 12Z Mon Sep 30 2024 - 12Z Tue Oct 01 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC/CENTRAL APPALACHIANS...

The lingering upper low over the East and accompanying moisture
from Helene will continue to produce some showers and thunderstorms
over portions of the Appalachians and Mid-Atlantic into Monday.
Heavy intensity and accumulations are not expected to be widespread
or heavy, however the recent wet period keeps an elevated threat
for excessive rainfall and isolated flooding concerns. A Marginal
remains in effect from south-central Virginia to central
Pennsylvania.

Campbell
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FOUS30 KWBC 290815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sun Sep 29 2024

Day 1
Valid 12Z Sun Sep 29 2024 - 12Z Mon Sep 30 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE INTERIOR MID-ATLANTIC...

...Mid-Atlantic/Central Appalachians...

Remnant moisture from Helene will remain caught up in the upper
trough pattern across the Ohio Valley while the mean trough begins
to slowly advance eastward through the period. During this period
precipitable water anomalies will be on the order of 1 to 2
standard deviations above normal and will encounter increased
forcing from the upper jet and modest lift through the column over
much of the Mid-Atlantic. This setup will support the development
of scattered to numerous thunderstorms that will likely have slower
storm motions. Recent rains have lowered local FFGs and increased
sensitivity across the region. Areal average QPF for the region
will be in the 1 to 3 inch range with isolated maximums in excess
of 3 inches will be possible. A Slight Risk for excessive rainfall
is in effect for extreme western Maryland, eastern West Virginia, northern/central/south-central Virginia and north-central North
Carolina. A Marginal Risk area spans from northeast
Georgia/northwest South Carolina to southern Pennsylvania and
southeast Ohio.

...Florida...

An unstable airmass coupled with lingering deep layer moisture
will promote isolated to widely scattered thunderstorm activity
capable of localized flooding, especially within urbanized zones.
Any of these storms will have the capability to produce 2 to 4
inches, especially along the coastline. A Marginal Risk for
excessive rainfall is in effect for central portions of the
peninsula.

Campbell


Day 2
Valid 12Z Mon Sep 30 2024 - 12Z Tue Oct 01 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE INTERIOR MID-ATLANTIC...

High pressure to the north, and a developing surface reflection
off the Mid-Atlantic coast thanks to the upstream trough will
create a persistent northeasterly flow setup with greater upslope
emphasis within the terrain across Western Virginia into the
far eastern West Virginia. There will be an enhancement of forcing
through the column of atmosphere near the Appalachian/Blue Ridge
spine that may result in hourly rainfall rates of 1 to 1.5
inches/hour during this period. Soils near saturation from recent
rains will keep the threat for flash flooding elevated for much of
this region thus maintained a Slight Risk for excessive rainfall
for extreme south-central Pennsylvania, western Maryland, eastern
West Virginia and northern/central Virginia. A Marginal Risk area
spans from northeast Tennessee/northwest North Carolina to southern Pennsylvania.

Campbell


Day 3
Valid 12Z Tue Oct 01 2024 - 12Z Wed Oct 02 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.


Campbell
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FOUS30 KWBC 300809
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Mon Sep 30 2024

Day 1
Valid 12Z Mon Sep 30 2024 - 12Z Tue Oct 01 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
EASTERN WEST VIRGINIA, VIRGINIA AND NORTHERN NORTH CAROLINA...

The latest guidance continues to show the south/southeast trend of
where the heaviest rain is expected to occur Monday across the
Virginias. During this time the slow moving upper low will be transferring
its energy to a coastal low feature located offshore Virginia and
North Carolina. This will likely lead to a prolonged local
enhancement in hourly rainfall rates near the Blue Ridge of 1 to
1.5 inches/hour during this period. Soils near saturation from
recent rains will keep the threat for flash flooding elevated for
much of this region. A Slight Risk for excessive rainfall remains
in effect for extreme eastern West Virginia, northern/central
Virginia, and north-central North Carolina. The Marginal Risk was
extended to cover much of coastal North Carolina in association
with the developing coastal low potentially locally increasing
rainfall totals due to slow- moving convection especially on the
western side of Pamlico Sound.

Campbell


Day 2
Valid 12Z Tue Oct 01 2024 - 12Z Wed Oct 02 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell


Day 3
Valid 12Z Wed Oct 02 2024 - 12Z Thu Oct 03 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell
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FOUS30 KWBC 011241
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
841 AM EDT Tue Oct 1 2024

Day 1
Valid 12Z Tue Oct 01 2024 - 12Z Wed Oct 02 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR SOUTHEAST
Virginia INTO NORTHEAST NORTH CAROLINA AS WELL AS FOR CENTRAL FLORIDA...

...Virginia/North Carolina...

During this period an area of low pressure will slide off the
Virginia and North Carolina coast while periods of heavy rainfall
persists from Richmond south and east through Hampton Roads and
portions of far northeastern North Carolina and the northern Outer
Banks. A majority of the rain is expected through about mid-
afternoon. Rain amounts and coverage with decrease as the low moves
further offshore. The inherited Marginal Risk was maintained albeit
with minor adjustments to reflect the latest model guidance and
WPC forecast.

...Central Florida...

A disturbance moving along the stationary front over central
Florida may support more widespread shower and thunderstorm
activity from Tampa through Orlando to the Space Coast Tuesday
afternoon. Training of the convection and impacts with the urban
centers may result in isolated flash flooding. The inherited Marginal
Risk was maintained with a minor southward expansion.

Campbell/Wegman


Day 2
Valid 12Z Wed Oct 02 2024 - 12Z Thu Oct 03 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

There will be a lingering potential for convection near the
eastern coastline that could result in bursts of modest or very
local heavy rainfall intensities. The threat for excessive rainfall
and flooding concerns will remain below the 5 percent threshold for
this period.

Campbell


Day 3
Valid 12Z Thu Oct 03 2024 - 12Z Fri Oct 04 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

There is a non zero possibility for locally modest to heavy
rainfall to move northward from the Gulf of Mexico along the Gulf
Coast anywhere from the Mississippi River delta to west of the
Florida bend. There is a fair amount of model spread that further
serves to decrease confidence on where any of these storms may
occur. At this time a trends suggest that the bulk of the heaviest
rainfall will remain south of the coastline.

Campbell
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FOUS30 KWBC 020757
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
357 AM EDT Wed Oct 2 2024

Day 1
Valid 12Z Wed Oct 02 2024 - 12Z Thu Oct 03 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

There will be a lingering potential for convection near the
eastern coastline that could result in bursts of modest or very
local heavy rainfall intensities. The threat for excessive rainfall
and flooding concerns will remain below the 5 percent threshold for
this period.

Campbell/Hamrick


Day 2
Valid 12Z Thu Oct 03 2024 - 12Z Fri Oct 04 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

For a few days now there has been a signal for moderate to possibly locally heavy rainfall to move northward from the Gulf of Mexico into far
southeast portions of Louisiana and up near the Mississippi River
delta. This is associated with moisture convergence along a quasi-
stationary frontal boundary over the northern Gulf of Mexico. There
have been a fair amount of spread on where and how much will occur
and that has not resolved much for this round of guidance. In
general consensus keeps the highest QPF over the Gulf while a
couple of solutions suggest 2-3+ inches may reach the coastal water
and the wetlands. In coordination with the local forecast office
in New Orleans the forecast QPF will likely not lead to any impacts
of significance for the wetland areas of southeast Louisiana
especially given their recent drier stretch. The Marginal Risk area
was removed for this period.

Campbell


Day 3
Valid 12Z Fri Oct 04 2024 - 12Z Sat Oct 05 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

As mentioned during the Day 2 period there has been a multi-day
pattern where the convection is just offshore the Gulf Coast but
within the convection there could be a few inches of isolated heavy
rainfall. The spread for this period favors a placement more over
the Gulf than the Gulf Coastline. There is a non zero potential for
localized moderate, possibly heavy rainfall intensities however
nothing that is expected to become problematic at this time.

Campbell
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FOUS30 KWBC 030828
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
428 AM EDT Thu Oct 3 2024

Day 1
Valid 12Z Thu Oct 03 2024 - 12Z Fri Oct 04 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

The latest guidance continues to have heavier QPF over the
Southeast Louisiana Parishes with areal averages of 2 to 3 inches
for areas along and south of I-10 from near New Orleans through
Biloxi towards Mobile, with some of the CAMs as much as 3 to 5
inches near the coastline. Spread persists in the placement of the
local maxima with the highest potential likely over either St.
Bernard or Plaquemines Parishes, both areas that are very difficult
to flood due to the swampy land structures and sandier soils that
limit flash flood potential.

Campbell


Day 2
Valid 12Z Fri Oct 04 2024 - 12Z Sat Oct 05 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

During this period there will be broad cyclonic over the Western
Gulf along with deep tropical air that advects into the flow. This
will result in convection that breaks out across the Gulf and
creeps inland into South Texas. A majority of the guidance
maintainsthe highest QPF offshore however there could be 0.75 to
1.5 inches that occurs in South Texas that should provide
beneficial moisture to the area rather than pose as an threat for
local flooding concerns.

Campbell


Day 3
Valid 12Z Sat Oct 05 2024 - 12Z Sun Oct 06 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Campbell

d
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FOUS30 KWBC 040733
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
333 AM EDT Fri Oct 4 2024

Day 1
Valid 12Z Fri Oct 04 2024 - 12Z Sat Oct 05 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 2
Valid 12Z Sat Oct 05 2024 - 12Z Sun Oct 06 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Sun Oct 06 2024 - 12Z Mon Oct 07 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR SOUTHWEST
FLORIDA AND THE LOWER KEYS...

A tropical wave or weak and slow-moving disturbance over the Gulf
will drift east into the Florida Peninsula Sunday. Multiple inches
of rain are expected through the day from Tampa south into the
Keys. The heaviest rain is expected Sunday afternoon and evening,
where added instability from diurnal heating will locally increase
rainfall rates. The slow-moving nature of any storms will be the
greatest contributor to flash flooding. FFGs have recovered since
Helene last week, so despite the forecast of 2-4 inches of rain
broadly over the Florida Gulf coast, only isolated flash flooding
is expected at this point.

Wegman
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FOUS30 KWBC 050745
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Sat Oct 5 2024

Day 1
Valid 12Z Sat Oct 05 2024 - 12Z Sun Oct 06 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR COASTAL DEEP
SOUTH TEXAS...

...Deep South Texas...

Easterly flow to the north of a developing but weak low over the
western Gulf that is the focus for widely scattered thunderstorm
activity over the Gulf is forcing storms to move inland from the
Gulf over Padre and South Padre Islands this morning. A cold front
will push south across Deep South Texas today, which will push the
tropical moisture south into Mexico, so the threat for flash
flooding is confined to the immediate coast down to Brownsville for
the day today. The flood threat should abate by tonight.

...South Florida...

The urban corridor of southeast Florida, including Miami may see
occasional heavy rain from westward-moving thunderstorms this
afternoon and evening. The storms should continue moving and weaken
as they move inland, so the threat while non-zero, should remain
under Marginal Risk levels. Better agreement in the CAMs may
necessitate a Marginal Risk issuance for this area with the midday
update.

Wegman


Day 2
Valid 12Z Sun Oct 06 2024 - 12Z Mon Oct 07 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
SOUTHERN FLORIDA PENINSULA...

A trough developing ahead of a slowly developing tropical low over
the Gulf will form over the southern Florida Peninsula on Sunday.
The air mass the trough will be developing in will be incredibly moisture-rich...with PWATs anywhere from 2.2 to 2.6 inches. This
will be close to the climatological maximum for this time of
year...between the 95th and 99th percentile and more than 3 sigma
above normal. The predominant mid-level wind flow will switch from northeasterly to southwesterly during the period, resulting in
chaotic storm motions. The heaviest rainfall totals will be along
both coasts, from Tampa south through Cape Coral on the Gulf Coast
as well as from the Treasure Coast south through Miami on the
Atlantic side. This bimodal distribution of QPF suggests
organization will be somewhat lacking, depending more on mesoscale
phenomena such as sea breezes or differential heating between the
urban areas and their surroundings.

This will likely be the first day of several where heavy rain will
be common and widespread across the Florida Peninsula. In the
increasingly likely event a tropical cyclone eventually develops in
the Gulf and moves towards the Florida Peninsula mid to late week,
this will be the first day of the predecessor rain event, or PRE.

Given high FFGs areally and this being the first day of the PRE, a
Marginal Risk was left intact for this area, but further increases
in forecast rainfall may require a Slight Risk for some of the
urban areas with future updates.

Wegman


Day 3
Valid 12Z Mon Oct 07 2024 - 12Z Tue Oct 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
FLORIDA PENINSULA...

Conditions across the Florida Peninsula will continue to
deteriorate on Monday. The PRE is expected to continue to
intensify, making for a second full day of periodic heavy rainfall
across the Peninsula. Both overall rainfall amounts and coverage
north up the Peninsula will increase on Monday as compared with
Sunday. All but the fastest guidance suggest that should a tropical
cyclone form over the Gulf, it will remain well west of the Florida
Peninsula through Monday night. This means the PRE will remain in
full force across the Peninsula. Once again, there will be a
bimodal distribution of the precipitation...but much more
pronounced. The focus will remain along both coasts, albeit heavier
and spread north. Given the expected heavy rainfall from Day
2/Sunday, by Monday most soils should be at or near saturation.
This means most of the day's rains will convert to runoff in most
areas.

With heavier rainfall expected in the urban areas along both
coasts, a Slight Risk upgrade was introduced with this update, in
coordination with MFL/Miami, FL; TBW/Tampa, FL; and MLB/Melbourne,
FL forecast offices. With better definition as to how and where any
tropical cyclone may develop over the Gulf, this will improve the
forecast for the PRE on Monday. This will apply both to where the
heaviest rain may occur as well as how heavy the amounts will be.
Further, with the hindsight of where Sunday's rainfall will occur,
it's possible additional upgrades may be needed with future
forecasts...though a preponderance of the guidance suggests any
direct effects of a potential tropical cyclone will hold until
after this period. Depending on how the heaviest rain areas align
on Monday with Sunday, some areas may be approaching 2 day totals
of 10 inches of rain by Tuesday morning. These amounts of rain in
any urban areas could approach Moderate Risk level impacts.

Wegman
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FOUS30 KWBC 060758
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
358 AM EDT Sun Oct 6 2024

Day 1
Valid 12Z Sun Oct 06 2024 - 12Z Mon Oct 07 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE MIAMI-
FORT LAUDERDALE METRO...

In coordination with the MFL/Miami, FL forecast office, a Moderate
Risk upgrade was introduced with this update.

A weak surface low is developing over the eastern Gulf well east of
T.S. Milton, but in the same plume of incredibly deep tropical
moisture. The low will drift southeastward toward south Florida.
This will increase the easterly flow over the Straits of Florida
between the Bahamas and Florida. This increased easterly flow in an
air mass with PWATs between 2.25 and 2.5 inches will both increase
the concentration and intensity of resultant thunderstorms over the
Gold Coast.

Portions of the Ft. Lauderdale and Miami metros saw up to 3 inches
of rain on Saturday. Rainfall amounts today and especially tonight
may accumulate to over 6 inches in that time. With saturated soils
and urban effects, the threat for ponding and flooding in the area
has greatly increased. Expect numerous areas of ponding and
flooding from today's rainfall, which necessitated the Moderate
Risk upgrade.

Elsewhere, the surrounding Slight Risk was expanded to include the
Gulf Coast from Tampa south and the Atlantic coast from Cape
Canaveral south. The aforementioned low will enhance rainfall rates
along much of the Gulf Coast from Tampa south, where heavy rainfall
Saturday caused localized flash flooding. This additional rainfall
on saturated soils will cause renewed flash flooding, mostly in
urban areas. Further north up the Atlantic coast, similar
convergence as further south is expected, but with lesser forcing,
resulting in lower rainfall amounts for the Treasure and Space
Coasts. Widely scattered instances of flash flooding are expected.

Finally, for the middle of the Florida Peninsula, the area will be
furthest from the strongest forcing, resulting in a local minimum
of rainfall. Since the area will not have tidal flooding concerns
and is somewhat less developed, only isolated flash flooding is
expected. The threat for heavy rainfall will continue up to the
Georgia coast however, where a local convergence zone may develop
as indicated in several of the CAMs. The Marginal was expanded
north to account for this possibility.

Wegman


Day 2
Valid 12Z Mon Oct 07 2024 - 12Z Tue Oct 08 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN FLORIDA PENINSULA AND THE KEYS...

The weak surface low that will bring heavy rain to south Florida on
Sunday will continue eastward over the Peninsula and into the
Bahamas by Monday afternoon. Heavy rain will likely continue over
the southern Peninsula through at least Monday morning. There is
considerable disagreement on the track, strength and the speed of
the low, which will play a major role in how long the heavy rain
persists into Monday afternoon. With somewhat better agreement that
rainfall amounts will at least be lower than on Sunday, the Slight
risk for the area that was inherited was largely maintained, albeit
including some of the interior of the Peninsula as soils become
saturated area-wide, resulting in close to 100% conversion of heavy
rain to runoff. An internal higher-end Slight is in place for the
Gold Coast, for the potential that should amounts from Sunday
verify, then another targeted Moderate Risk upgrade will be
necessary. Meanwhile, a second day of very heavy rain and
thunderstorms is expected to impact all of the Keys, which at high
tide times may cause flooding due to poor drainage.

With some of the other CAMs moving the low across the southern
Peninsula and east to the Bahamas, portions of the Gulf Coast,
especially north of Ft. Myers/Cape Coral up through Tampa are in
the rare decreasing trend in the forecast rainfall amounts on
Monday. Thus, the Slight that extended up through Tampa was
downgraded to a Marginal north of Ft. Myers/Cape Coral with this
update.

Wegman


Day 3
Valid 12Z Tue Oct 08 2024 - 12Z Wed Oct 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
FLORIDA PENINSULA...

The PRE (predecessor rain event) will enter its third and final day
over the Florida Peninsula on Tuesday. The trough that occasionally
spins up weak surface lows will remain in place across the
Peninsula. The circulation of what will then be Hurricane Milton
will make its approach to the Gulf Coast of Florida, likely near
Tampa very late Tuesday night/early Wednesday morning. At this
time, expect little of the rainfall directly associated with
Milton's core to yet impact the Florida Peninsula. Of course, with
future updates and forecast changes from NHC, this may change.
Given the inherent uncertainty with the track and speed of this
small hurricane, the Slight over the Peninsula was maintained,
albeit with some filling in in the middle of the Peninsula near the
Orlando area. There remains a bimodal distribution of the rain with
much more expected along the Gulf coast from Tampa down through
Naples, but with a secondary maximum for the Space and First
Coasts.

With the latest guidance, there is some offset of the axis of
heaviest rainfall ahead of Milton. The northward trend will reduce
amounts in portions of the hard-hit Gold Coast in favor of more
rain for the northern Peninsula towards the First Coast. By Tuesday
the greatest overlap will be over the Gulf Coast. It is here than
an internal higher-end Slight was introduced for the Tampa through
Naples area due to increasing amounts of heavy rain moving into the
coast, being moved along by the predominant southwesterly flow in
the trough ahead of Milton's core circulation. Heavy rainfall both
the past couple days as well as expected both today and Tuesday
should keep all of the soils on the Florida Peninsula at or near
saturation, resulting in nearly all of the rainfall converting to
runoff. Thus, progressively less rainfall will be needed to result
in flooding.

Despite Milton and directly associated rains largely holding to the
Day 4/Wednesday period, it appears that similar to Helene, most of
the rain over the Florida Peninsula will be associated with the
PRE, while the heaviest rain (as well as wind and storm surge) will
conclude the multi-day rain event with Milton moving through,
causing much more widespread flooding.

Wegman
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FOUS30 KWBC 070823
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
423 AM EDT Mon Oct 7 2024

Day 1
Valid 12Z Mon Oct 07 2024 - 12Z Tue Oct 08 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE GOLD
COAST AND THE UPPER FLORIDA KEYS...

Very few changes were made to the inherited EROs for this period.

A leading low, front, and surface trough over the eastern Gulf and
Florida well ahead of Hurricane Milton continues to spread rain
over nearly all of the Florida Peninsula this morning. The low will
shift east over the Everglades and South Florida today. Ahead of
the low, additional showers and thunderstorms capable of very heavy
rainfall rates due to the extremely moist environment will
continue. Portions of the Gold Coast saw 2-4 inches of rain
yesterday, resulting in localized flash flooding, so the potential
for that much rain again today supports the continuance of the
Moderate Risk. The trailing front south and west of the low will
remain stationary near Southwest Florida and the Keys. This will
keep the threat for heavy rainfall ongoing through tonight. The
Slight Risk area remains in place for these regions as far
southwest Florida is the swampy Everglades and the Keys present
very small targets for heavy rain. If training cells were to move
over the Keys during high tide then flooding is probable.

HREF probabilities suggest the heaviest rain today all over south
Florida are more likely to remain offshore, so the heavy rain
threat is slightly lower today compared to yesterday/Sunday.
Convergence along the Atlantic coast remains prevalent today, so
the Slight Risk remains in place to the north through the Space and
Treasure Coasts. With the center of the low tracking over south
Florida and off to the east towards the Bahamas, this should give
the likely landfall areas of the Gulf Coast north of Ft. Myers
through Tampa a general reprieve from heavy rain for most of today.

Wegman


Day 2
Valid 12Z Tue Oct 08 2024 - 12Z Wed Oct 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
FLORIDA PENINSULA...

There will be a general lull in the overall general rainfall across
Florida on Tuesday. The "calm before the storm". The low impacting
most of the state Monday will be well east of the Bahamas by
Tuesday, while the rainfall directly associated with Hurricane
Milton will likely remain off or just arriving at the Gulf Coast
before 12Z Wednesday. Nevertheless, widespread light to moderate
rainfall will impact the state Tuesday and Tuesday night. Thus, any
resultant flooding will be largely due to favorable antecedent
conditions due to generally widespread saturated soils across the
Peninsula. Further, continued extremely moist atmospheric
conditions consistent with the deep tropical air mass with PWATs
around 2.25 inches will still support locally heavy rainfall with
any convection that manages to form.

On the Atlantic side, a convergence zone may remain over the Space
and Treasure Coasts on Tuesday, which could locally organize any
convection and result in locally heavier rainfall over these mostly
urban areas. Meanwhile over the Gold Coast, a local minimum of
rainfall may develop, but the heavy rain there the past couple days
as well as some chance of shower and thunderstorm activity may
cause widely scattered localized flooding. No changes were made to
the ERO risk areas.

Wegman


Day 3
Valid 12Z Wed Oct 09 2024 - 12Z Thu Oct 10 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR CENTRAL AND
NORTH FLORIDA AS WELL AS FAR SOUTHEASTERN GEORGIA...

The main circulation of Hurricane Milton will cross the Florida
Peninsula on Wednesday. There remains considerable uncertainty as
to where the center will make landfall, which will of course play a
huge role as to where the heaviest rainfall amounts will be. See
the NHC forecast for the latest track. The storm is expected to be
undergoing increasing shear, beginning extratropical transition,
growing in size, and ingesting dry air. Thus, there is decent
agreement that at landfall, the storm will be weakening. This
should help to reduce the rainfall south of the circulation center
as dry air ingestion associated with extratropical transition
should quickly erode the rain-producing storms southwest of the
center. Very dry air behind a southward moving front will greatly
cut into rainfall amounts on the northern fringe of the
circulation. Thus, expect there to be a tight gradient of rainfall
both on the south and north sides of the circulation, but for
different reasons. The ERO risk areas have been expanded in both
directions due to track and storm size uncertainties, especially
towards the north, with the Moderate Risk expanded into far
southeastern Georgia, and the surrounding Slight and Marginal
expanded into the Low Country of coastal southern South Carolina.
This may be optimistic, but these expansions were made primarily
due to uncertainties, and will likely be refined in the coming
days.

For the moment, there are several reasons a High Risk was not
considered in no particular order: 1) The storm will be weakening
prior to landfall which may temper rainfall amounts a little bit,
2) Milton's small size should reduce the areal coverage of the
heaviest rain, 3) The primary rain footprint of Milton over north
Florida will largely miss where the hardest hit areas of the PRE in
south Florida are. Of course there is some overlap, but not nearly
as much as with Helene, 4) The core of the heaviest rain at the
moment is expected to track from north of Tampa northeast through
around Jacksonville. This area has been relatively dry in recent
days compared to areas further south, 5) Milton will be moving
quickly and accelerating. This will reduce the time the heaviest
rain has along and north of the track to result in widespread and
numerous flash floods, 6) The inclusion of CAMs and higher
certainty with the track may help to narrow down where a potential
High Risk may be needed with future forecasts. For now with Day 3
being outside the CAMs time range, the large Moderate will
suffice.

Wegman
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FOUS30 KWBC 080816
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
416 AM EDT Tue Oct 8 2024

Day 1
Valid 12Z Tue Oct 08 2024 - 12Z Wed Oct 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
FLORIDA PENINSULA...

No significant changes were made to the ERO risk areas for this period.

"The calm before the storm" will be in place over much of Florida
today. This isn't to say it won't rain anywhere...but the risk of
heavy rain causing flooding on most of the Peninsula today will
most certainly be the lowest of the next few days. A stationary
front in the same tropical moisture plume as Milton is draped
across southern Florida. This is providing a focus for heavier
showers and storms south of the front from Miami south through the
Keys. Since the storms are tracking parallel to the front, training
is a significant concern this morning. As any mesolow tracking
along the front moves off, the heavy rain threat in the Keys should
diminish by this afternoon due to increasing influence of Milton.
For the rest of the Florida Peninsula, most of today should be dry,
especially the further north you go. This is because drier air
associated with a jet across the Panhandle is sinking southward
with a front and will ultimately catch Milton and force
extratropical transition as it approaches Florida. For today
however, it will keep things largely dry along and north of the
eventual track of the storm.

The rainfall threat (and the basis for the ongoing Slight) is
largely tied to any showers and storms that may form...most likely
from mesoscale effects like differential heating and sea breezes.
Due to an excess of atmospheric moisture over most of Florida with
PWATs of 2.25 to 2.75 inches today, any storms that form, even if
disorganized and not associated with any discernible forcing...will
have a superabundance of moisture to work with to convert to
rainfall. Much of south Florida has seen multiple inches of rain
over the past few days. While not prolific enough to cause
widespread flooding concerns, they have kept soils close to
saturated. This will play a role in the eventual flooding concerns
with Milton. 00Z HREF guidance highlights portions of the Treasure
Coast with the highest chances of 3 inches or more of rain today
not directly associated with Milton.

A higher end Slight remains in place for the Gulf Coast from Tampa
south through Naples. This is largely tied to the initial rain
bands from Milton which will begin to impact the coast in the
predawn hours Wednesday before the start of the Day 2 period.

Wegman


Day 2
Valid 12Z Wed Oct 09 2024 - 12Z Thu Oct 10 2024

...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CENTRAL FLORIDA...

...WIDESPREAD AND NUMEROUS INSTANCES OF FLASH FLOODING ARE
EXPECTED WITH LIFE-THREATENING AND CATASTROPHIC FLASH FLOODING PROBABLE...

With the ingestion of some of the longer range CAMs into the model
suite, the forecasted rainfall directly associated with Hurricane
Milton's crossing of the Florida Peninsula has increased markedly
from previous forecasts. The latest storm total rainfall has over
11 inches of rain for Tampa, 8 inches near and north of Orlando,
and 5.5 inches for Jacksonville. The corridor of the High risk
following the entire length of I-4 has seen the most impactful
increases in forecasted rainfall. Obviously there has been a nearly
historic increase in Milton's strength in the last 24 hours, and
all of this added energy and Gulf moisture will mean more rainfall
to come along its track, despite its fast forward speed.

The heaviest rainfall amounts along I-4 and north will generally
will be immediately along and north of the most probable track of
Milton's center. As mentioned in the NHC discussions, Milton is
expected to be well into the process of extratropical transition by
the time the storm crosses the Peninsula. This process should
greatly limit the amount of rainfall expected south of the center,
as dry air entrainment into the southwest quadrant of the storm is
an essential aspect of the extratropical transition process. Thus,
nearly all of the impressive tropical moisture associated with
Milton will be focused along and north of the center, and therefore
represents the greatest threats for flash flooding. The ERO risk
categories drop off a bit slower on the south side since the
predecessor rainfall event (PRE) of the past couple days and today
was largely focused on south Florida, as the stationary front that
has been there has persisted. Inflow into Milton's circulation and
the eventual development of a cold front south of the center
should still lead to bands of rain criss-crossing south Florida
from west to east. Since the PRE saturated this area the most...the
lesser amounts of rain expected here may still cause flooding
impacts...so the ERO risk categories south of the track may be a
bit generous.

Meanwhile on the north side of the circulation, abundant dry air
associated with a separate cold front and jet streak over the
Panhandle and far north Florida should act as a very effective sink
for the portion of Milton's rainfall that drifts too far away from
the center. Since this area has been quite dry in recent days, the
threat for flooding will be much more constricted, and therefore
the ERO risk categories are much more compact.

The additional rainfall now in the forecast will be one factor for flooding...while another one will be storm surge and tidal
flooding, especially south of the center where the flow will be
onshore and to a slightly lesser but still impactful extent, to
the north of the center on the Atlantic side where there will also
be onshore flow. At the time of high tide and the storm surge, the
added water from the Gulf/Atlantic will effectively block effective
drainage from the rainfall falling over the interior. The 6-12
inches (with locally higher amounts of rainfall) having nowhere to
drain due to the high tide and storm surge flooding will also work
to exacerbate the flooding impacts from Milton since that rain
water will have nowhere to drain.

Given all of the above, and despite the small to medium size of the
storm and the acceleration of the storm in the forecast, a High
Risk was introduced in coordination with TBW/Tampa, FL;
MLB/Melbourne, FL, and JAX/Jacksonville, FL forecast offices. It's
probable that the greatest flooding impacts will be with storm
surge primarily, but also the portions of the nearshore rivers,
streams, and creeks (especially near landfall) where the inland
flood waters from heavy rainfall are unable to drain to the Gulf.

Wegman


Day 3
Valid 12Z Thu Oct 10 2024 - 12Z Fri Oct 11 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR ORLANDO AND
PORTIONS OF THE FIRST AND SPACE COASTS...

A rare double upgrade was introduced with this update, with
potential for further adjustments with future updates. The latest
guidance suggests that the wraparound rain to the north and
northwest of the center of Milton will persist well into the day on
Thursday. Thus, associated forecast rainfall has increased
markedly from the previous forecasts. For the Moderate Risk area,
expect an additional 2 to 4 inches of rain after the 12Z/8am
Thursday start of the day 3 period. With a High Risk on Day 2,
further increases in the forecast rainfall may require a High Risk
in this general area to continue into Thursday. Obviously,
adjustments in the speed and track of Milton as it races off the
coast will result in additional big changes to this ERO forecast.

Essentially, the Day 3 ERO is just a continuation of the Day 2
rainfall with Milton. The vast majority of the rainfall for the
period will fall during the day Thursday, and expect trimming and
downgrades through the day as the rain ends from west to east.
Expect widespread and catastrophic flooding from the Day 2 period
to continue through the Day 3 period as the rain ends.

Wegman
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FOUS30 KWBC 100827
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
427 AM EDT Thu Oct 10 2024

Day 1
Valid 12Z Thu Oct 10 2024 - 12Z Fri Oct 11 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
EAST-CENTRAL TO NORTHEAST FLORIDA...

Heavy rainfall from Milton continues to quickly move east across
the Florida Peninsula. Additional rain of 1 to 4 inches is likely
over the next couple hours along portions of the central and
northern FL east coast. However based on recent radar and HRRR
trends it appears likely that most, if not all, of this heavier
rain will be offshore by 12z this morning. Thus while areas of
considerable flash flooding will continue over the next few hours,
the expectation is that additional flash flooding after 12z will be
minimal. For that reason we will carry only a Marginal risk on the
new day 1 ERO that goes into effect at 12z this morning. The
ongoing High risk remains valid for the next couple hours until
12z. Keep in mind that even after the heavy rain ends, significant
areal and river flooding will continue to be a concern in areas
that have received significant rainfall.

Chenard


Day 2
Valid 12Z Fri Oct 11 2024 - 12Z Sat Oct 12 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Chenard


Day 3
Valid 12Z Sat Oct 12 2024 - 12Z Sun Oct 13 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Chenard

d
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FOUS30 KWBC 110721
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
321 AM EDT Fri Oct 11 2024

Day 1
Valid 12Z Fri Oct 11 2024 - 12Z Sat Oct 12 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Easterly low level flow will bring showery conditions to the
central and southeast Atlantic coast of FL today into tonight.
However with PWs below 2" and instability limited not currently
expecting rainfall rates or totals to reach levels of concern for
flash flooding. Thus we will continue to carry no risk area in the
ERO.

Chenard


Day 2
Valid 12Z Sat Oct 12 2024 - 12Z Sun Oct 13 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

Moisture and instability return northward into southern FL Saturday
into Saturday night, with PWs increasing towards 2.25" and CAPE
over 1000 j/kg. Meanwhile a weak wave moving into the eastern Gulf
of Mexico may result in an uptick in low level flow and
convergence. Thus expect we should gradually see an uptick in
convective coverage this weekend over the Keys into south FL.

Easterly low level flow and westerly upper level winds support the
potential for slow moving convective cells near the coastal
convergence axis. Timing remains a bit uncertain, and the better
convective coverage may end up more over the Keys this period
(where flash flooding is harder to come by), but given the
increasing moisture and instability there is at least a conditional
threat of localized flash flooding Saturday into Saturday night
into the more urban areas of southeast FL. If deep convection does
indeed develop then urban flash flooding is possible from the
upper Keys into southeast FL.

Chenard


Day 3
Valid 12Z Sun Oct 13 2024 - 12Z Mon Oct 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

The risk on day 3 is a continuation of the threat on day 2 over
Southeast FL. The overall thermodynamic ingredients remain the
same, however there is a chance that forcing will be stronger by
Sunday. Still some timing and positional differences amongst the
guidance, but the general consensus is for a weak wave to move
across FL Sunday, which should both result in a subtle uptick in
mid/upper forcing and locally enhance lower level convergence.

Thus currently expecting a greater chance of loosely organized
convective clusters Sunday into Sunday night...and with wind fields
still supporting slow moving cells...this activity could tend to
anchor along the coastal convergence axis for a while. Thus
isolated urban flash flooding is considered possible. Certainly a
chance that a Slight risk may be needed for one of these weekend
days...but given some uncertainty with the synoptic evolution and
convective coverage, think a good first step is just introducing
Marginal risks for both days 2 and 3 (Sat and Sun) and continue to
monitor trends.

Chenard
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FOUS30 KWBC 120752
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
352 AM EDT Sat Oct 12 2024

Day 1
Valid 12Z Sat Oct 12 2024 - 12Z Sun Oct 13 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

Moisture and instability return northward into southern Florida
today which should result in deeper convection and the potential
for higher rainfall rates with PWs increasing towards 2.25".
Meanwhile a weak wave moving into the eastern Gulf of Mexico should
result in an uptick in low level flow and convergence. Thus expect
we should gradually see an uptick in deeper convective coverage
over the Keys into south FL and the adjacent waters today into
tonight.

The overall synoptic pattern still looks to favor slow moving
convective cells along and near the coastal convergence axis given
easterly low level flow and westerly upper level winds. Timing and
the CAPE distribution over land remain a bit uncertain. Some model
guidance wants to keep the better instability and convergence
offshore or over the Keys, while others shift these ingredients
more into the Southeast Fl coastal urban corridor. This decreases
confidence with regards to convective evolution.

The ingredients in place in the vicinity certainly support the
potential for a localized higher end flash flood event somewhere
within the southeast FL urban corridor today and/or tonight.
However the signal in the 00z HREF guidance is mixed, and overall
just not seeing enough in the probability fields to suggest we are
at Slight risk level coverage or confidence at this time. Thus we
will maintain the Marginal risk and continue to monitor
observational and model trends.

Chenard


Day 2
Valid 12Z Sun Oct 13 2024 - 12Z Mon Oct 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

The risk on day 2 is a continuation of the threat on day 1 over
Southeast Florida. The overall thermodynamic ingredients remain
similar, however there is still spread with the mesoscale to
synoptic setup. The 00z GFS and ECMWF have trended quicker with the
weak wave and suggest the better organized convective risk Sunday
will now be offshore and over the Bahamas. However the Gem Reg and
some HREF members appear slower and focus more convection over
south FL.

The uncertainty in these details appears too large to go with
anything more than a Marginal risk at this time. Overall do tend to
think the flood risk Sunday is trending down compared to what it
looked like last night (given the trends noted in the ECMWF and
GFS), but favorable moisture and instability parameters suggest at
least a localized flash flood risk could persist.

Chenard


Day 3
Valid 12Z Mon Oct 14 2024 - 12Z Tue Oct 15 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Chenard
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FOUS30 KWBC 130801
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
401 AM EDT Sun Oct 13 2024

Day 1
Valid 12Z Sun Oct 13 2024 - 12Z Mon Oct 14 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER FLORIDA KEYS INTO THE SOUTHEAST FLORIDA URBAN CORRIDOR...

No changes were made to the inherited Marginal risk area over the
southeast FL urban corridor. Isolated convection will be ongoing at
12z this morning along the coastal convergence axis...with another
round of activity likely this afternoon. It is the afternoon
convection that appears to have better instability to work with,
and thus a better chance of more robust development. Coverage
remains a question, but high res guidance suggests a weak surface
trough/wave moving across south FL should help locally enhance
convergence this afternoon.

With any deeper convection tapping into the stronger westerly flow
aloft, the tendency may be for cells to have more of an eastward
motion this afternoon, limiting rainfall duration as cells move
offshore. However if low level easterly flow is strong enough
and/or the low level convergence axis is persistent enough, then
we could see at least some cell training for a period of time.
Overall the ingredients are in place to suggest a localized flash
flood risk is a possibility. HREF guidance supports isolated 3"
totals, but there is minimal model support for amounts much higher
than that. The Marginal risk should cover this isolated urban
flash flood threat...as not seeing enough support for Slight risk
level impacts/coverage at this time.

Chenard


Day 2
Valid 12Z Mon Oct 14 2024 - 12Z Tue Oct 15 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Chenard


Day 3
Valid 12Z Tue Oct 15 2024 - 12Z Wed Oct 16 2024

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Chenard
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FOUS30 KWBC 160802
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
402 AM EDT Wed Oct 16 2024

Day 1
Valid 12Z Wed Oct 16 2024 - 12Z Thu Oct 17 2024

The probability of rainfall exceeding flash flood guidance is less than
5 percent.

Kleebauer


Day 2
Valid 12Z Thu Oct 17 2024 - 12Z Fri Oct 18 2024

...2030Z Update...

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer


Day 3
Valid 12Z Fri Oct 18 2024 - 12Z Sat Oct 19 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN NEW MEXICO INTO SOUTHERN COLORADO...

Longwave pattern will evolve into a fairly prolific upper
trough/closed-low over the Great Basin, slowly migrating eastward
with sights on the Four Corners. Large scale ascent will become
maximized downstream of the mean trough with a pronounced diffluent
pattern in-of the Southern Rockies, including the Sangre de Cristo
and San Juan mountain ranges where heavier precip is forecast. A
cold front will slowly propagate eastward from the primary
disturbance with a return flow setup pressing westward across the
Eastern NM plains on the western flank of a sprawling surface high
east of the Mississippi. A secondary cold front to the north will
plunge southward thanks to a strong ridge of high pressure
developing upstream in wake of the primary western low, along with
a lee side trough developing over the Front Range. The tandem of
boundaries and backed flow will converge over Northern NM with a
strong isentropic ascent pattern initiating later Friday evening
through Saturday AM and beyond.

Convective signals are most pronounced in the initial stages of
the pattern evolution mainly due to the return flow setup where
more unstable air will advect northwestward into the Eastern NM
plains before banking against the lee of the Southern Rockies. Both
ensemble and deterministic output for heavy precip are locked in
across the area encompassing much of Northern NM, but especially
within the confines of places like Raton and points south where
topographic enhancement within the convergent axis will generate
local precip maxima when the convergence pattern truly solidifies
late in the period. Totals of 1-2" of precip are forecast on the
southern edge of the San Juans down into portions of the Sangre de
Cristos, closing in on some of the prevalent burn scars in the
region. A secondary maxima of 1-2" is forecast over that main axis
of convergence over Northeastern NM in vicinity of the eastern
flank of the Sangre de Cristos, including places like Taos and
Angel Fire over into parts of the plains in the lee of the mountain
chain. The period before will be more of a primer for the main
event this period through the following D4 time frame. The
combination of better moisture return and large scale forcing via
diffluent mid- level flow and jet coupling provides ample support
for a continuation of the previous MRGL risk, as well as an
expansion of the risk area further southwest and east to match the
ensemble QPF footprint in areas of highest convective potential.

Kleebauer
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FOUS30 KWBC 170804
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
404 AM EDT Thu Oct 17 2024

Day 1
Valid 12Z Thu Oct 17 2024 - 12Z Fri Oct 18 2024

Relative progressive nature of precipitation across Northern NM
will alleviate much of the flash flood concerns this afternoon,
however the very low FFG's in place over each existing burn scar
within the Sangre de Cristos will offer an opportunity for
localized flooding within each impacted zone. Current HREF probs
for >1" of precip is around 50-60% within the neighborhood derived
analysis. This is still very lacking within the EAS prob field
leading to a pattern of less widespread heavier precipitation
totals and more relegated to very localized maxima likely over the
tops of the mountain chain. The best depiction is outlined over the
San Juan Mountains where a majority of the precipitation will fall
as snow or a rain/snow mix mitigating the threat for flash flooding
during the period. This has allowed for a continuation of the nil
ERO across the CONUS, but still a non-zero presence within the burn
scars of Northern NM.

The probability of rainfall exceeding flash flood guidance is less than
5 percent.

Kleebauer


Day 2
Valid 12Z Fri Oct 18 2024 - 12Z Sat Oct 19 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE FOUR CORNERS REGION THROUGH NORTHERN NEW MEXICO...

Longwave pattern will continue evolving into a fairly prolific
upper trough/closed-low over the Great Basin, slowly migrating
eastward with sights on the Four Corners. Large scale ascent will
become maximized downstream of the mean trough with a pronounced
diffluent pattern in-of the Southern Rockies, including the Sangre
de Cristo and San Juan mountain ranges where heavier precip is
forecast. A cold front will slowly propagate eastward from the
primary disturbance with a return flow setup pressing westward
across the Eastern NM plains on the western flank of a sprawling
surface high east of the Mississippi. A secondary cold front to the
north will plunge southward thanks to a strong ridge of high
pressure developing upstream in wake of the primary western low,
along with a lee side trough developing over the Front Range. The
tandem of boundaries and backed flow will converge over Northern NM
with a strong isentropic ascent pattern initiating later Friday
evening through Saturday AM and beyond.

There has been very little deviation in the guidance to amass much
of a change compared to the previous forecast, so a general
continuity was maintained from the inherited MRGL risk across the
Four Corners into Northern NM. Ensemble guidance is in relative
agreement on the placement of two maxima during the forecast
period; one located Northeast AZ into Southeast UT with the initial
diffluent signature ahead of the evolving upper low over the Great
Basin, and the secondary maxima across Northeastern NM where the
convergence pattern aided by increasing large scale ascent will
generate a period of heavier precip Friday evening into Saturday
morning and beyond. Each areal maxima is similar with regards to
precip magnitude with a general neighborhood 1-2" max with a small
chance at upwards of 2.5" across the western maxima within the best
upper ascent within the nose of the 100kt 250mb jet streak. The
secondary maxima is generally within the last 12-hr window
encompassing 00-12z Saturday with the heaviest QPF footprint
actually highest in D3 (More on that in the D3 period below). In
any case, the very dry antecedent conditions, slot canyons, and
flashier river basins within the Four Corners area will offer a
greater risk of flash flooding with a secondary threat over the
remnant burn scars in Northern NM. This allowed for a maintenance
of the previous MRGL risk.

Kleebauer


Day 3
Valid 12Z Sat Oct 19 2024 - 12Z Sun Oct 20 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS
OF THE SOUTHERN HIGH PLAINS INTO SOUTHEASTERN COLORADO...

Closed upper circulation will slowly migrate eastward with a
persistent diffluent channel focused in-of the Eastern NM High
Plains up into the Colorado Front Range for Saturday. A uni-
directional flow located within the lowest 600mb will persistent
through much, if not all the forecast period allowing for moist
unstable air to be pulled poleward into the confines of the Caprock
and points north. ECENS PWAT anomalies are forecast to run upwards
of 3-3.5 deviations above normal with an M-Climate Percentile
(Forecasts relative to the last 20 years during time of year) that
is peeking into the seasonal max, a testament to the anomalous
nature of the moisture advection regime. With the poleward
advancement of the airmass, regional theta-E's spike with a theta-E
ridge positioning located right over the NM/TX border running clear
into Front Range of CO and nearby KS. This signal is consistent
with a persistent band of rainfall likely to be situated within the
theta-E ridge mentioned above and just out ahead of the slow-moving quasi-stationary front trailing the very slow moving to perhaps stationary
low pressure across Southern CO.

Precip totals of 2-4" with locally higher amounts are increasingly
likely within that corridor between Clovis up through Southeastern
CO with the max likely driven by repeating convection as small
mid-level perturbations rotate around the general upper circulation
and move overhead of the areas above. The only saving grace for a
more significant flash flood potential is the antecedent conditions
leading in are very dry with the 0-10cm relative soil moisture
percentiles running between 5-20% across the area anticipated to
see the most rainfall. Initial rains will be beneficial, but will
add through the course of the period with waves of heavier rain
likely exacerbating areas by later in the period into early Sunday.
The previous SLGT risk was generally maintained with a MRGL
surrounding. Both risks were expanded somewhat on the southern and
northern peripheries to account for a trend in an expansion of
precip latitudinally in either direction. The heaviest will likely
encompass Eastern NM into Southeast CO with these areas likely
trending towards the higher end of SLGT risk if the signal remains
and/or amplifies further.

Kleebauer
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