Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sun Jul 16 2023 04:00:41

AWUS01 KWNH 160400
FFGMPD
VAZ000-NCZ000-WVZ000-TNZ000-161000-

Mesoscale Precipitation Discussion 0743
NWS Weather Prediction Center College Park MD
1158 PM EDT Sat Jul 15 2023

Areas affected...Much of VA...portions of southern WV...northern
NC

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

Valid 160400Z - 161000Z

Summary...Localized 1-2"/hr rainfall rates to continue over
already saturated areas. Additional flash flooding is likely, and
some significant flash flooding with life threatening impacts is
possible.

Discussion...A favorable axis for training heavy showers and
thunderstorms is setting up across portions of the Mid-Atlantic
overnight, as a pair of MCVs/vorticity maxima look to merge over
portions of central VA that have recently had 1-3" of rainfall
over the past 3-6 hours. The mesoscale environment out ahead of
(and surrounding) these mid-level impulses is characterized by ML
CAPE of 500-1000 J/kg, precipitable water values of 1.8-2.2 inches
(near the max moving average, per RNK/IAD sounding climatology),
and effective bulk shear of 20-30 kts. In addition, the 850-300 mb
mean wind is oriented parallel to a surface trough on the lee of
the Appalachians (and to the axis where heavy rainfall has already
occured), increasing the concerns for additional training over the
same areas of central VA. The exceptionally moist tropospheric
column and DPVA via the mesoscale forcing should continue to
support 1-2"/hr rainfall rates, and MRMS FLASH is also indicating
that flash flooding impacts are imminent or already occurring in
the vicinity of Lynchburg (CREST maximum unit streamflow values of
200-600 cfs/smi). There is also ground truth to these estimates,
as numerous reports of flooded and impassable roadways have
recently been received from the area.

HRRR runs from 21-02z suggest the potential for an additional 1-3"
of rainfall over much of the same areas through 10z, and the new
00z HREF probability matched mean (PMM) has increased relative to
the 12z/18z suite, suggesting similar localized totals. Digging
deeper, the HREF 40-km neighborhood probabilities are even more
impressive, indicating the potential for 3" and 5" exceedance (per
20-30% and 5-10% values, respectively). This would suggest that
additional flash flooding is likely, particularly along this axis
in central VA. Should these high-end 3-5"+ totals occur over much
of the same areas, significant flash flooding is possible with
life threatening impacts.

Churchill

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!8ydF_HLbReKrLv2KszbqMDwFhcy3L6jqPjRoE83uyat764dqEMvUdX0eUw1CeNad3p6g=
NMSwXwUug3zSIeg5ZfdTbX8$  for graphic product...

ATTN...WFO...AKQ...GSP...LWX...MRX...RAH...RLX...RNK...

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

LAT...LON   38617878 38487750 37717657 36867718 36287813=20
            35647920 35608030 36038156 36428172 36848158=20
            37368181 37928184 38298118 38537989=20

=3D =3D =3D
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