Mesoscale Precipitation Discussion 0700
NWS Weather Prediction Center College Park MD
224 PM EDT Mon Aug 20 2018

Areas affected...Northeast AR...Southeast MO...Southern IL

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

Valid 201823Z - 210023Z

Summary...Heavy showers and thunderstorms will continue to develop
and increase in coverage.  Some of these storms may train over the
same area and lead to some instances of flash flooding for this
afternoon.

Discussion...Radar and satellite imagery has been showing an
increase in shower and thunderstorm activity over southeast
Missouri in the warm sector of an anomalous mid-latitude cyclone. 
The convection is developing in response to increasing
destabilization in the boundary layer and diffluent flow aloft
ahead of the 500mb closed low and accompanying slow moving cold
front.  MLCAPE is forecast to increase into the 1500 to 2500 J/kg
range for southeast Missouri and especially into northeast
Arkansas.  Model forecast soundings are suggesting deep layer
unidirectional flow from the southwest and this will support
back-building convection and therefore periods of very heavy rain
with rates near 2 inches per hour at times. 

The latest suite of high res model guidance continues to depict
patchy areas of greater than 2 inches of rain through 7 pm local
time.  Although flash flood guidance values are not particularly
low, the high rainfall rates may be enough to overcome this and
possibly lead to instances of flash flooding.

D. Hamrick

ATTN...WFO...ILX...LSX...LZK...MEG...PAH...SGF...

ATTN...RFC...ABRFC...LMRFC...MBRFC...NCRFC...OHRFC...

LAT...LON   39918936 39848867 39548801 39068766 38538774
            37758817 37278854 36728895 36078937 35558984
            35339053 35349131 35509243 35809291 36299300
            36939239 38039135 38819081 39289053 39728991