Mesoscale Precipitation Discussion 0619
NWS Weather Prediction Center College Park MD
203 AM EDT Thu Aug 09 2018

Areas affected...ArkLaTex into central/southern AR and northwest
MS

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

Valid 090600Z - 091200Z

Summary....Flash flooding will be possible across portions of the
ArkLaTex into central/southern AR and northwestern MS through 12Z.
Where the greatest cell training occurs, 3-5 inches of rainfall
are expected.

Discussion...0530Z radar imagery showed scattered, elevated
convection occurring from northeastern TX into south-central AR.
This activity was located 50-100 miles north of a remnant outflow
boundary which stretched from north-central TX into northern LA,
roughly along I-20. An MCV was depicted on the last few frames of
visible and more recent "clean window" IR satellite imagery over
southeastern OK with convective development just ahead of this
feature. Farther east, convection seems to have aligned with 850
mb confluent flow.

MUCAPE via the latest SPC mesoanalysis showed a minimum over
central and eastern AR but with 500-1500 J/kg to the west and
south amid GPS derived precipitable water values of 1.7 to about
2.0 inches. KSHV and KLZK one hour rainfall estimates have been
increasing amid the expanding convection and continued development
appears likely though the remainder of the morning. RAP guidance
shows enhanced 850 mb flow of 20-25 kt to the southeast of the MCV
with forecast expansion into southern AR by 12Z. Given the
overrunning nature of the low level flow across the remnant
outflow boundary, increasing CAPE and mean steering flow parallel
to the surface boundary, training echoes of heavy rain are
expected to increase over the next few hours with pockets of 3-5
inches possible by 12Z from the ArkLaTex into southern and central
AR. Flash flood guidance is lower across northern locations (about
2.5 to 3+ inches in 3 hours), but these values are expected to be
exceeded in a few locations through 12Z.

Otto

ATTN...WFO...FWD...JAN...LZK...MEG...OUN...SHV...TSA...

ATTN...RFC...ABRFC...LMRFC...WGRFC...

LAT...LON   35129403 35129299 34979193 34779119 34449049
            33859068 33499175 33339460 33309591 33369669
            33819676 34209625 34419552 34809487