Mesoscale Precipitation Discussion 0999
NWS Weather Prediction Center College Park MD
514 PM EDT Wed Oct 31 2018

Areas affected...Mid-South into the Ohio Valley

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

Valid 312113Z - 010313Z

Summary...Convergence of subtropical moisture on a stationary
front will continue to allow repeating thunderstorms with hourly
rates up to 2 inches this evening from northern AR and up the
lower OH River Valley.

Discussion...A stationary front persists from AR into the lower OH
Valley. Broad southerly flow provides subtropical moisture (sfc
dewpoints in the mid 60s) that encounters instability of 1000-1500
J/kg per latest RAP mesoanalysis. PWATs are around 1.5" per 20Z
GPS data, which is 2 to 2.5 standard deviations above normal.

A favorable flash flood setup is developing along this narrow
frontal zone which is oriented with the deep layer southwesterly
flow. Some squall activity is noted in north-central AR which may
shift the front some, but otherwise little movement is expected in
precipitation over this area into late tonight.

Flash flood guidance is generally 2.5 to 3 inches in three hours,
so the local rain rates of 1.5 to 2" per hour (as recently seen
near KPAH) could cause flash flooding to begin in the near future
with the threat lasting at least through midnight.

Jackson

ATTN...WFO...ILN...LMK...LZK...MEG...OHX...PAH...SGF...

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

LAT...LON   38828506 37408514 34369254 35109364 36099232
            38058758