430
AWUS01 KWNH 221702
FFGMPD
TNZ000-KYZ000-ILZ000-MSZ000-MOZ000-ARZ000-222300-

Mesoscale Precipitation Discussion 0302
NWS Weather Prediction Center College Park MD
102 PM EDT Wed May 22 2024

Areas affected...The Ozarks eastward into the Tennessee Valley

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

Valid 221700Z - 222300Z

Summary...Showers and thunderstorms blossoming ahead of a cold
front will expand and train into the evening. Rainfall rates as
much as 2-3"/hr are likely, which could produce 2-3" of rain with
local amounts as much as 5". Flash flooding is possible.

Discussion...The GOES-E IR imagery this afternoon indicates
rapidly expanding and intensifying convection noted by cooling
cloud tops from eastern KY through northern AR. These storms are
developing along/ahead of a southward advancing cold front
analyzed by WPC draped from southern IN, through the Bootheel of
MO, and into eastern OK. This front is moving into favorable
thermodynamics for heavy rain rates, reflected by GPS measured PWs
as high as 1.9 inches over AR, near the daily record at LZK, and
SPC RAP analyzed SBCAPE as high as 4000 J/kg. Into these
impressive thermodynamics, forcing for ascent is intensifying
through low-level convergence aided by a convectively enhanced
shortwave lifting out of OK, and an overlap of thickness and upper
level diffluence downstream into the TN VLY. Within this robust
environment, radar-estimated rain rates have already reached 1"/hr.

As the aftn progresses, it is likely convection will become
widespread ahead of this front as suggested by many of the
available high-res CAMs. This is supported by the presence of the
deep layer ascent acting upon an environment that will become
increasingly unstable as a pool of higher SBCAPE gets drawn
northeast ahead of the front. This will likely produce expansion
and intensification of the thunderstorms, with HREF neighborhood
probabilities for 2"/hr rain rates reaching 20-30%, and HRRR
15-min rainfall suggesting brief rates above 3"/hr, especially
where storm organization can occur in the presence of 30-40 kts of
bulk shear. Most concerning for the flash flood potential is that
this convection should train on 850-300mb flow that is progressive
at 20-25 kts, but aligned parallel to the front. With an intense
pool of SBCAPE focused over AR, this flow should allow for
regeneration and training from SW to NE, prolonging these rain
rates in some areas. This is reflected by HREF probabilities for
3"/6hrs reaching 25% in some areas, with minimal, but non-zero,
probabilities for 5" in the next 6 hours also present.

FFG across the region is generally elevated at around 2.5"/3hrs,
but pockets of 7-day rainfall which has been above 150% of normal
according to AHPS has locally reduced FFG. Where the most intense
rain rates occur, or where training is most prevalent, instances
of flash flooding are possible.


Weiss

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...LMK...LZK...MEG...OHX...PAH...

ATTN...RFC...ABRFC...LMRFC...OHRFC...NWC...

LAT...LON   37378824 37338732 37018609 36418553 35958607
            35488722 34828884 34569025 34559142 34579167
            34599236 34779309 35109345 35559330 35959240
            36609040 37178918