491
AWUS01 KWNH 240050
FFGMPD
VAZ000-NCZ000-TNZ000-KYZ000-INZ000-240500-

Mesoscale Precipitation Discussion 0311
NWS Weather Prediction Center College Park MD
850 PM EDT Thu May 23 2024

Areas affected...eastern/central Tennessee and much of Kentucky

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

Valid 240049Z - 240500Z

Summary...Showers and thunderstorms developing ahead of a
shortwave will continue for a few more hours across Tennessee and
Kentucky. Rain rates exceeding 1"/hr are likely, and where
repeated rounds of convection occur, additional rainfall of 1-3"
is possible. This could produce instances of flash flooding.

Discussion...The regional radar mosaic this evening shows a
cluster of thunderstorms moving through eastern TN and KY, with
secondary scattered development occurring in its wake across
central TN. This activity is forming in response to subtle PVA and
height falls downstream of a shortwave ejecting from western KY,
and a subtly enhanced 850mb LLJ arcing out of the SW at 20-25 kts.
These local forcing mechanisms are occurring in a region of large
scale ascent due to upper diffluence in a region of modest, but
coupled, upper jet streaks. The deep layer ascent is acting upon
favorable thermodynamics noted by PWs of 1.5-1.6 inches, around
the 90th percentile for the date according to the SPC sounding
climatology, with collocated MUCAPE of 1000-2000 J/kg, despite
substantial decrease in instability the past 3 hours. 12-hr
rainfall according to MRMS has been 1 to as much as 3 inches
across the area, priming soils for the rest of the night.

Although the CAMs are struggling with the ongoing development
behind the more impressive line, the recent HRRR has started to
indicate that at least some isolated activity will continue across
TN/KY. While there is lowered confidence in the exact evolution
due to a lack of model support, the environment will remain
favorable for a few more hours before instability wanes or gets
overturned, which should support additional thunderstorm
development downstream of the primary shortwave. In the favorable
thermodynamics, any storms should be able to support 1"/hr
rainfall, with locally more intense rainfall possible at times.
Additionally, these storms will have the potential to train west
to east as Corfidi vectors become aligned to the mean 0-6km wind,
and development occurs to the W/SW in the pool of greater
instability. This could result in streaks of 1-3" of rain as
progged by 10-20% HREF neighborhood probabilities for 3"/6hrs.
Loss of instability due to nightfall and overturning with this
second area of convection, combined with the eastward progression
of the shortwave, should result in rapid waning of coverage by 05Z.

Although coverage may be isolated to scattered through the next
several hours, any additional heavy rain could result in rapid
runoff as NASA SPoRT 0-10cm RSM is above 80% due to heavy rain
today adding to 7-day rainfall that has been in some places above
150% of normal. This has reduced FFG to as low as 1-2"/3hrs in
many areas, favoring at least isolated instances of flash flooding
where heavy rain moves across these sensitive soils.


Weiss

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

ATTN...WFO...GSP...HUN...ILN...JKL...LMK...MRX...OHX...PAH...
RLX...

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

LAT...LON   38638435 38288323 37648265 36608260 35318344
            35048436 35018503 35108591 35218647 35518691
            36288716 36938717 37828664 38468549