FOUS30 KWBC 270836
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
436 AM EDT Fri Sep 27 2024

Day 1
Valid 12Z Fri Sep 27 2024 - 12Z Sat Sep 28 2024

...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR THE BLUE RIDGE OF
NORTH CAROLINA...

...CATASTROPHIC FLASH FLOODING WILL LIKELY BE ONGOING FRIDAY MORNING...

...Southern Appalachians...

As the dissipating circulation center of Helene continues to move
northward today bands of heavy rain will overspread the Southern
Appalachians focusing some of the highest amounts along the Blue
Ridge of North Carolina. With likely well over 12 inches of rain
having fallen in this area prior to the start of the period at
12Z/8am Friday, this quick hit of as much as 6 inches of additional
rain in 6 hours will likely push any flooding rivers, streams and
creeks into major/catastrophic flooding stage. Te High Risk is
exclusively for Friday morning with the last of Helene's
rainfall...albeit again some of the heaviest in terms of intensity.
Once the circulation center passes (and largely dissipates as it
moves into the mountains), all of the significant rainfall
associated with Helene will finally be over in this region.

A broad rain shield will linger over Virginia and West Virginia as
Helene pivots northward. This part of the region will continue to
be sensitive to the additional rain and flooding. Despite slightly
lower amounts of total rain expected, numerous instances of flash
flooding are expected. The Moderate Risk was maintained for far
northwest South Carolina, western North Carolina, and portions of
eastern Tennessee, West Virginia and Virginia.

...Ohio, Tennessee, & Mid-Mississippi Valleys...

The westward portion of Helene's circulation will interact with a
strong upper level low whose nearly stationary movement has been
partially responsible for the northward surge of tropical moisture
associated with the PRE as well as Helene's northward movement.
Once the circulation center nears Atlanta Friday morning, it will
turn more northwestward into central Tennessee, then stall out
there for an extended period of time, maybe even 2 days.

A fair amount of the tropical moisture will advect westward into
the Ohio, Tennessee and Mid-Mississippi Valley to help support
locally heavy rain across Kentucky and Tennessee. The latest model
guidance and CAMs are depicting a swath of 2 to 4+ inches over
urban or flood prone areas thus a Moderate Risk was upgraded for
this period for western and central Tennessee.

Campbell/Wegman


Day 2
Valid 12Z Sat Sep 28 2024 - 12Z Sun Sep 29 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
MIDDLE TO LOWER OHIO RIVER VALLEY...

Lingering rain associated with the combined upper low and Helene
will continue mainly across the Ohio Valley into Saturday morning.
Any flooding impacts may be realized to their greatest extent
along this portion of the Ohio River on Saturday. A Slight Risk
remains in effect for portions of the Ohio River Valley although
with an eastward and southward adjustment to reflect the latest
trends and observations. Additionally, southern portions of the Northeast/northern Mid-Atlantic were trimmed out of the Marginal
Risk area due to drier antecedent conditions and not as much
rainfall from Helene and the frontal system as once expected.

Campbell


Day 3
Valid 12Z Sun Sep 29 2024 - 12Z Mon Sep 30 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE EASTERN Tennessee VALLEY/SOUTHERN Appalachians AND MID-
ATLANTIC REGION...

Remnant energy and moisture from Helene will still be present over
the region with lingering rain over extra sensitive soils. Some
locations will likely have ongoing riverine flooding and additional
rain amounts may aggravate the situation. A Marginal Risk for
excessive rainfall remains in effect from Tennessee and Kentucky to
points east to Maryland.

Campbell
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