AWUS01 KWNH 262036
FFGMPD
VAZ000-NCZ000-SCZ000-GAZ000-TNZ000-270230-

Mesoscale Precipitation Discussion 1069
NWS Weather Prediction Center College Park MD
435 PM EDT Thu Sep 26 2024

Areas affected...North Georgia, Western Carolinas into Virginia

Concerning...Heavy rainfall...Flash flooding likely

Valid 262034Z - 270230Z

Summary...Swaths of heavy rain rates ahead of Helene will continue
through this evening over portions of north Georgia and the
western Carolinas into Southwest Virginia, including mainly the
eastern side of the Southern Appalachians. Rainfall rates of
1-2"/hr will continue, which through repeating rounds could
produce 2-3" of rain and local maxima of 5" through 02Z. This will
enhance flash flooding, with significant impacts
continuing/expanding.

Discussion...The regional radar mosaic late this afternoon shows
continued swaths of heavy rain over north Georgia and western SC
with continued enhancements of rainfall over the eastern slopes of
the Southern Appalachians. This is associated with a pronounced
moisture plume streaming north from Hurricane Helene which is now
west of Tampa Bay. PWs within this moisture plume have been are
2.25 to 2.5" with southeasterly flow of 20 to 35kt over central
GA/SC expected to shift over the southern Appalachians over the
next couple hours. Instability remains limited, 200 to 500 J/kg of
MUCAPE, but deep layer ascent is impressive. Mid-level divergence
between Helene and a pronounced upper low remaining over far
western TN is combining with a nearly stationary poleward arcing
jet streak from AL to KY with favorable right entrance dynamics
over the region. In this environment, recent rainfall rates are
estimated from KGSP and KFFC as up to 1.5"/hr which can be
expected to continue through the evening. There is a notable gap
in reflectivity over southeast GA and north FL Peninsula between
bands, which should provide relief over the next few hours for
southern portions of this outlook area.

The impressive moisture advection combining with nearly unchanging
robust ascent will result in continuous rainfall into areas that
have already received 4 to 10" in the past 24 hours. This rainfall
occurring atop saturated soils, sensitive terrain, and ongoing
flash flooding with further enhanced impacts across the region
which is still prior to the actual intense rainfall from Helene
herself. This additional rainfall should quickly result in further life-threatening flash flooding.

Locally catastrophic rainfall impacts are expected overnight as
the core of Helene approaches, so please pay attention to further
discussions and see the latest info on Helene at hurricanes dot
gov.

Jackson

ATTN...WFO...CAE...CHS...FFC...GSP...MRX...RNK...

ATTN...RFC...LMRFC...OHRFC...SERFC...NWC...

LAT...LON 36978187 36798079 35098067 33848074 32548124
33028323 33988422 34478481 35358494 35808371
36188283 36578241
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