Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Aug 22 2025 04:32:04

AWUS01 KWNH 220431
FFGMPD
VAZ000-NCZ000-WVZ000-SCZ000-221000-

Mesoscale Precipitation Discussion 0971
NWS Weather Prediction Center College Park MD
1231 AM EDT Fri Aug 22 2025

Areas affected...west-central VA/NC into surrounding portions of
WV/SC

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

Valid 220430Z - 221000Z

Summary...Slow moving, highly efficient heavy rainfall with rates
up to 2-3"/hr will maintain a flash flood risk overnight.
Localized totals of 5"+ may lead to isolated instances of
significant, life threatening flash flooding.

Discussion...As Hurricane Erin continues to move eastward over the
open seas of the western North Atlantic, the storm seems to be
indirectly contributing to a much more localized heavy rainfall
event over portions of eastern VA into the eastern Carolinas. A
massive anticyclonic wave break (AWB) is quite apparent over the
western North Atlantic (characterized by low-PV air aloft injected
from the tropics), contributing significantly to a blocked
upper-level pattern/jet stream aloft. This blocking aloft has
resulted in weak steering flow from the surface to the mid-upper
levels with only a very weak/subtle trough apparent in the
mid-levels (along with effective bulk shear of less than 20 kts).
However, a PV (potential vorticity) streamer aloft (~250-300 mb)
is associated with a narrow 40-50 kt jet streak (that is crucially
quasi-stationary due the diabatically educed blocking from Erin)
which has allowed for broad top-down driven ascent. Pockets of
slow moving convection resulting from this upper-level feature
(along with the other necessary components for heavy rainfall,
including a pocket of deep tropospheric moisture with PWs of
1.4-2.0" and MLCAPE of 500-1000 J/kg) are continuing to produce
localized rainfall rates up to 2-3"/hr.

Going forward, the slow southward propagation of convection is
likely to continue (towards the pool of higher surface thetaE and
associated MLCAPE 1000+ J/kg) with the 00z HREF mean storm motions
appropriately indicating 10-15 kt S-SSW storm motions. While
localized redevelopment further north cannot be ruled out in the
neat term (as lingering instability still exists over portions of
WV/VA that already received significantly locally heavy rainfall
earlier), the threat going forward is certainly greatest for areas
farther south (including Charlotte, NC and surrounding portions of
NC/SC) where HREF probabilities for 3" and 5" exceedance are as
high as 40-50% and 20-30%, respectively (which corresponds with
25-35% probs for Flash Flood Guidance exceedance and up to 10%
probs of 100-yr ARI exceedance). Isolated to scattered instances
of flash flooding are possible, and localized totals of 5"+ may
lead to isolated instances of significant, life threatening flash
flooding (with particular concern for these totals occurring in
more sensitive portions of the greater Charlotte metropolitan
area).

Churchill

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!8Ujuz1WCLeHlyxv2eoo8DiIqpJnJhZ-9TkcGl4_e7EJw9seQhpze2XnOOdXcn2xIKbWX=
8tA1F4HGmZpz8gtA0oNF1S0$  for graphic product...

ATTN...WFO...CAE...GSP...ILM...RAH...RLX...RNK...

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

LAT...LON   38218001 37667980 37187977 36847988 36477974=20
            36077982 35008014 34677994 34018017 34238091=20
            34438157 34918201 35888214 36278153 36618097=20
            37368057 37988071=20

=3D =3D =3D
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