Mesoscale Precipitation Discussion 0806
NWS Weather Prediction Center College Park MD
328 PM EDT Sat Sep 08 2018

Areas affected...C/E AR, NW MS, W TN, MO Bootheel, W KY

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

Valid 081927Z - 090115Z

Summary...Scattered to numerous thunderstorms should continue
developing this afternoon along and ahead of a cold front in
portions of the Mid Mississippi Valley and Arkansas. Most storms
should produce 1-2 in/hr rain rates, with the strongest storms
possibly reaching 3 in/hr rates. This could produce flash flooding.

Discussion...The area from western Kentucky southwest into
Arkansas has been relatively clear on GOES-16 visible satellite
for much of the day, and convection was beginning to develop in
earnest between 18Z and 1930Z ahead of an approaching front. A
plume of very high precipitable water values was situated in the
same region, with the CIRA blended TPW product and RAP analysis
showing values of around 2.2 to 2.3 inches. Furthermore, with the
relatively unobstructed daytime heating, strong instability has
developed with MLCAPE values around 2000-2500 j/kg. The
combination of strong instability with a deep plume of tropical
moisture should yield relatively organized convection with the
potential for high rain rates. Even though the mesoscale setup is
not ideal for training, relatively unidirectional winds in the
troposphere could favor a modest training component to the storm
motions as convective bands should have a tendency to align with
the deep layer mean wind. Rain rates of 2 in/hr seem achievable in
this environment, with 3 in/hr rain rates possible given adequate
training of strong convection. The lowest flash flood guidance in
the region was over east-central Arkansas, and this did align with
some of the higher probabilities for 2+ in/hr rain rates (per the
12Z HREF).

Lamers

ATTN...WFO...JAN...LZK...MEG...OHX...PAH...SHV...

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

LAT...LON   37278854 37118776 35778861 34429017 33509124
            33279204 33619324 34459311 35489226 36189057