Mesoscale Precipitation Discussion 0682
NWS Weather Prediction Center College Park MD
339 PM EDT Fri Aug 17 2018

Areas affected...Central/Southern AR...Northeast LA...Central
MS...West-Central AL

Concerning...Heavy rainfall...Flash flooding likely

Valid 171939Z - 180139Z

Summary...Showers and thunderstorms will become more numerous and
expand southeast over the next few hours. A combination of heavy
rainfall rates, cell-mergers and repeating of cells will foster
enhanced concerns for flash flooding.

Discussion...The latest GOES-16 IR satellite imagery is showing
cooling convective tops over south-central to southeast AR and
expanding into western and and central MS as convectively driven
outflow boundaries advance southeast and into a very moist and
unstable airmass. MLCAPE values are exceeding 2500 j/kg just to
the south of two distinct boundaries, and a reflection of this
instability is showing up in visible satellite imagery with well
defined SW/NE oriented cloud streets highlighting a moderate CU
field.

Showers and thunderstorms will become more numerous over the next
couple of hours and will become more aligned NW/SE with the mean
layer flow. This will support a scenario where convection will
have the capability of merging and training over the same area
going through the late afternoon and early evening hours as the
aforementioned outflow boundaries tend to become aligned more
parallel to the mean flow.

The PWATS across the region are quite high and generally 2 to 2.25
inches which will promote highly efficient rainfall processes and
extremely heavy rainfall rates considering the degree of favorable
thermodynamics. Expect rainfall totals going through mid-evening
to be as high as 3 to 5+ inches. Some flash flooding will be
likely as a result.

Orrison

ATTN...WFO...BMX...JAN...LZK...MEG...MOB...SHV...

ATTN...RFC...ABRFC...LMRFC...SERFC...

LAT...LON   34569254 34109074 33468929 32748785 32168745
            31718806 31848936 32049019 32369121 32659213
            33099324 33699427 34219443 34559404