Mesoscale Precipitation Discussion 889
NWS Weather Prediction Center College Park MD
1050 PM EDT Sun Sep 23 2018

Areas affected...Northern MS...West-central TN...Northwest Alabama

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

Valid 240249Z - 240749Z

Summary...Showers and thunderstorms are expected to continue in a
tropical airmass during the late evening and early morning hours.
Heavy rainfall rates and wet antecedent conditions may be enough
to result in some flash flooding.

Discussion...Atmospheric conditions remain favorable for
additional heavy showers and storms going into the early morning
hours.  A quasi-stationary frontal boundary is draped across
northern MS and extending NE to the AL/TN border.  There has been
very limited overall eastward progression with this boundary
today, and this is allowing for a continued surge of deep tropical
moisture northward that is getting lifted by the surface front. 
Aloft, the presence of an upper level jet over the southern Ohio
River Valley and a modest 500mb vortmax is further aiding ascent.

PWATs across the region remain quite high with values of 1.8 to
2.3 inches based on recent GPS data, with the greatest moisture
concentrated across northern MS.  This is supported by the 00Z JAN
sounding with 2.16 inch PW and a deep saturated warm cloud layer. 
Given the depth of moisture and 500-1000 J/kg of MUCAPE, highly
efficient rainfall processes are likely to result in enhanced
rainfall rates with hourly amounts of 1 to 2 inches possible
within stronger convective cores.

The latest high res model suite is indicating the potential for
swaths of 1.5 to locally 3 inches of rainfall through 8Z.  It does
appear based on recent radar trends that the model QPF maxima are
perhaps farther west than where the heaviest rain is likely in the
near term.  The antecedent conditions are quite wet across much of
central TN and northern MS, with additional rainfall only
aggravating any existing run-off issues.

D. Hamrick

ATTN...WFO...BMX...HUN...JAN...MEG...MRX...OHX...

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

LAT...LON   36478781 36478659 36328565 35958528 35328537
            35098560 34748605 34408659 34268694 33968778
            33418849 32958890 32478931 32438992 32709043
            33289069 34299028 35208966 36118884