Mesoscale Precipitation Discussion 0735
NWS Weather Prediction Center College Park MD
430 PM EDT Wed Aug 29 2018

Areas affected...eastern OK into AR

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

Valid 292027Z - 300115Z

Summary...Slow moving cells will have the potential to produce
localized rainfall maxima of 3-5 inches through 01Z over portions
of eastern OK into central AR. Given rain rates of 2-3 in/hr,
flash flooding may occur.

Discussion...Surface observations and radar imagery showed a slow
moving outflow boundary at 20Z stretching from northwest AR to
near BVX and then east-northeastward into the MO Bootheel.
Convective cells have had a history of developing just ahead of
the outflow boundary with little to no movement, producing
observed rainfall rates of 2-3 in/hr, as seen in Stone county AR
ending 20Z. The steadily progressing outflow boundary eventually
catches up with these slow moving cells, ending the short term
flash flood threat. Storm motions have initially been slow due to
5-15 kt cloud-bearing layer mean flow. Given an environment
characterized by precipitable water values near 2 inches and
MLCAPE of 2500-3500 J/kg via the 19Z SPC mesoanalysis, additional
cells will have the potential to produce heavy rain rates of 2-3
in/hr.

Farther west, visible satellite imagery showed an ill-defined area
of lift tied to a weak low-mid level wave over southeastern KS
with a southward extending area of cumulus/lift into northeastern
OK. This may become a source of renewed convective development
over the next couple of hours as the area of lift moves toward the
OK/AR border and into a better thermodynamic environment.

The expectation is for continued localized convective development
through the remaining hours of peak heating across central AR
ahead of the southward progressing outflow boundary, where a few
cells have popped up on radar imagery, capable of 2-3 in/hr rain
rates and possible flash flooding. Additional development between
21-00Z will be possible near eastern OK into western AR if capping
can be overcome. Overall, localized rainfall of 3-5 inches will be
possible with isolated flash flooding.

Otto

ATTN...WFO...LZK...MEG...PAH...SGF...TSA...

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

LAT...LON   36739485 36639360 36349129 36478954 35948922
            35468965 34809135 34709292 34899458 35269561
            35749597 36289581