Weather Prediction Center issues Mesoscale Precipitation Discussion #820 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE276
AWUS01 KWNH 221350
FFGMPD
VAZ000-NCZ000-WVZ000-TNZ000-KYZ000-221800-
Mesoscale Precipitation Discussion 0820
NWS Weather Prediction Center College Park MD
948 AM EDT Wed Jul 22 2026
Areas affected...Tennessee, western North Carolina, southwest
Virginia
Concerning...Heavy rainfall...Flash flooding possible
Valid 221348Z - 221800Z
Summary...Training showers and thunderstorms will continue a flash
flood risk into the afternoon. Rainfall rates of 2+"/hr could
cause an additional 2-4" of rainfall atop vulnerable soils and
terrain.
Discussion...The regional radar mosaic this morning shows a narrow
line of thunderstorms extending SW to NE across much of Tennessee
and into western Virginia. This activity is bubbling along a 925mb
convergence axis, into which moisture confluence is intensifying
on slowly veering 850mb inflow around a ridge to the east. This
inflow is additionally drawing elevated PWs (measured via GPS of
1.7 to 2.0 inches, and via the BMX 12Z U/A sounding above the 90th
climatological percentile) into a narrow corridor of
already-elevated MLCAPE around 1000 J/kg. This has resulted in
recent MRMS hourly rainfall as much as 2 inches northeast of
Knoxville, TN.
There continues to be some uncertainty as to the convective
evolution through the aftn, but at least locally excessive rain is
likely. The CAMs are generally too far north with the current
activity, but they suggest convection will gradually sink south
through the day as a slow moving cold front drops into the area.
While the exact evolution (and thus placement of heaviest
rainfall) is still uncertain, there is high confidence that
training of echoes containing rainfall rates of at least 1-2"/hr
(locally higher according to the 15-min HRRR) will persist into
the afternoon. The HREF and REFS exceedance probabilities for 3
inches in the next 6 hours are 15-30% in far northeast TN, but
locally higher rainfall is likely, and the ECMWF EFI also has a
focus for highest probability (>0.95) and SoT above +2 across far
northeast TN, indicating strong agreement across multiple ensemble
systems.
This area is generally sensitive to heavy rain rates due to the
natural vulnerability of the terrain in the Appalachians, as well
as compromised FFG as low as 0.5-1.5"/3hrs due to recent heavy
rainfall. While the threat will be greatest where heavy rain falls
across these more vulnerable areas, any training of 2"/hr rain
rates into the afternoon could result in flash flooding instances.
Weiss
...Please see www.wpc.ncep.noaa.gov for graphic product...
ATTN...WFO...GSP...HUN...JKL...MRX...OHX...RAH...RLX...RNK...
ATTN...RFC...ALR...ORN...RHA...TIR...NWC...
LAT...LON 37358114 37297990 37017886 36687901 36237978
35898079 35588189 35358288 35148393 35038506
35088602 35238681 35378741 35848740 36078682
37258243
Source:
Weather Prediction Center issues Mesoscale Precipitation Discussion #820 concerning HEAVY RAINFALL...FLASH FLOODING POSSIBLE---------------
If I'm using your data in a way that is against your terms please email the team at "threatweb@pupswoof117.com"! I am a bot who will not respond in the comments at all and is only designed to post RSS feeds!
