AWUS01 KWNH 311222
FFGMPD
VAZ000-NCZ000-OHZ000-GAZ000-TNZ000-KYZ000-INZ000-311730-

Mesoscale Precipitation Discussion 0764
NWS Weather Prediction Center College Park MD
822 AM EDT Wed Jul 31 2024

Areas affected...eastern Kentcuky, eastern Tennessee

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

Valid 311221Z - 311730Z

Summary...Showers and thunderstorms developing ahead of a
vorticity maxima will expand into eastern KY and TN this morning.
Rainfall rates of 1-2"/hr are likely, which may produce spots of
1-3" of rainfall leading to instances of flash flooding.

Discussion...The regional radar mosaic this morning depicts a
rapid expansion of convective activity from far southern Ohio
southward through Kentucky and into northern Tennessee. This
convection is blossoming immediately downstream of a compact but
potent vorticity maxima analyzed by the RAP and noted in the
GOES-E WV imagery embedded within the broad NW flow. The
accompanying PVA and subtle height falls are combining with weak
LFQ diffluence to produce locally enhanced ascent. This lift is
impinging into impressive thermodynamics as W/NW 850mb flow surges
MUCAPE of 1000-2000 J/kg eastward to combine with PWs of 1.5 to
1.8 inches to produce an environment favorable for heavy rain
rates.

The guidance is struggling to resolve any of the ongoing activity,
and it appears the high-res CAMs are generally missing the
accompanying vorticity impulse responsible for this convection.
The ARW and ARW2 are really the only two that suggest this morning
activity should be occurring, so the evolution the next few hours
is significantly dependent on an ingredients based approach and
these two outputs. As bulk shear increases to 25-35 kts in the
presence of the mid-level impulse, and the more robust
thermodynamics get advected eastward, this should result in an
expansion of convection with some organization into clusters
through the late morning. Despite the lack of model agreement, the
HREF neighborhood probabilities suggest rainfall rates have a
20-40% chance of exceeding 1"/hr, supported by the elevated CAPE
and PWs. Although mean 0-6km winds are progressive at 15-20 kts,
aligned propagation vectors to the long-axis of the developing
convection could result in at least short-term training from NW to
SE, resulting in corridors of 1-3" of rainfall.

This region has been extremely wet recently with 7-day AHPS
rainfall anomalies reaching 150-300% of normal in southern KY and
much of eastern TN. This has caused a lowering of 3-hr FFG to less
than 1.5" in many places, for which the HREF forecasts a 20-25%
chance of exceedance despite a lack of model agreement.
Additionally, MRMS 24-hr rainfall has been 2-4", which resulted in
some instances of flash flooding yesterday. While flash flooding
is not expected to be widespread, any heavy rain rates falling
atop urban areas or sensitive soils could cause impacts.


Weiss

ATTN...WFO...FFC...GSP...ILN...JKL...LMK...MRX...OHX...RLX...

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

LAT...LON   39378478 38968373 37848276 36888248 36058253 
            35548268 34988353 34838420 34898480 35558561 
            37088602 38528558 
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