Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Aug 15 2025 19:11:09

AWUS01 KWNH 151910
FFGMPD
NCZ000-SCZ000-GAZ000-TNZ000-ALZ000-160000-

Mesoscale Precipitation Discussion 0940
NWS Weather Prediction Center College Park MD
309 PM EDT Fri Aug 15 2025

Areas affected...northern AL/GA into adjacent portions of TN/NC/SC

Concerning...Heavy rainfall...Flash flooding possible

Valid 151905Z - 160000Z

Summary...Increasing thunderstorm coverage into the late afternoon
with locally heavy rainfall (as high as 2-3"/hr rates) may result
in isolated to scattered instances of flash flooding.

Discussion...A distinct upper-level trough (most apparent above
400 mb, associated with a PV anomaly apparently originating from
cyclonic wave breaking) centered near the Midsouth is allowing for
greater coverage of convection into downstream portions of TN/AL.
The mesoscale environment is characterized by high tropospheric
moisture (1.7-2.1" PWs, at or above the 90th percentile per FFC
sounding climatology), effecitve bulk shear (25-30 kts, also at or
above 90th percentile), and plentiful instability (SBCAPE
2500-4500 J/kg). While the environment is lacking a surface
boundary or focusing mechanism to efficiently organize convection,
the increased coverage of cells alone will be sufficient to result
in cell mergers and outflow boundary collisions to result in
localized training/repeating of heavy rainfall rates (with as much
as 2-3"/hr with the strongest updrafts, as deep layer mean flow of
only 5-10 kts allows for longer residence times of assicated
downdrafts).

Hi-res CAMs are in relatively good agreement concerning both the
precise spatial overlap of heavier convection (per HREF EAS 0.5"
exceedance probs of 15-25% from east-central AL through northeast
GA into adjacent portions NC/SC) and chances for localized heavy
totals (40-km neighborhood 3" exceedance probs of 15-35%,
generally along and north of the highest EAS probs). 3-hr FFGs
across the region generally range from 2.0-3.0", suggesting
relatively high chances for localized FFG exceedance (HREF 40-km
probs for 3-hr FFG exceedance equating to 15-35% as well). Given
the overall favorable environment and recent observational trends,
isolated to scattered instances of flash flooding are possible
through dusk. While some convection may linger into the evening
hours, coverage and intensity should be diminishing overall with
the dry air/subsidence associated with the backside of the upper
trough ending heavy rainfall for northern/western portions (i.e.
AL/TN) of the MPD first.

Churchill

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!7LFF506LU6Y4ZM3Y29zYooJXw8vlpISsn8eYKNcHiiZ-FbtuEOKGzRZwI9XeJD2GPxcO=
Pef0tkOtvzQleUUW5Wtzoag$  for graphic product...

ATTN...WFO...BMX...CAE...FFC...GSP...HUN...MRX...OHX...

ATTN...RFC...ALR...ORN...TIR...NWC...

LAT...LON   36428474 36028423 35668359 35598242 35298191=20
            34648208 33928253 33518282 33208322 33088357=20
            32998420 33078483 33208536 33158588 33148642=20
            33608692 34498655 35468649 35828557 36338516=20
=20=20=20=20=20=20=20=20=20=20=20=20

=3D =3D =3D
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