Mesoscale Precipitation Discussion 0695
NWS Weather Prediction Center College Park MD
922 PM EDT Sun Aug 19 2018

Areas affected...North-Central AR

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

Valid 200121Z - 200521Z

Summary...A band of thunderstorms with heavy rain has formed over
northern AR.  Hourly rain totals to 2.5" with local amounts to 5"
are possible.

Discussion...A cluster of thunderstorms has been broadening to the
northeast of a mesoscale wave in northwest AR well ahead of the
main cold front.  Precipitable water values of 2-2.25" lie here
per GPS data and the Little Rock AR sounding.  Inflow is
convergent at 20-25 knots per VAD wind profiles, importing ML CAPE
values of 2500-3000 J/kg into the area.  The area is divergent
aloft to the southeast of a deep layered low located across KS. 
Effective bulk shear of 30 knots and a fairly unidirectional flow
out of the west-southwest has allowed for the formation of this
band.

Recent HRRR/RAP runs seem to have some handle on what is expected
over the next several hours.  The 850 hPa winds are expected to
veer somewhat, which should allow the mesoscale wave and its
attendant convection to continue moving eastward within the ML
CAPE gradient at 20-25 kts, roughly parallel to the 1000-500 hPa
thickness pattern.  The main heavy rain threats are embedded
mesocyclones, training, and random cell mergers with individual
storms that move northward into the band.  Hourly rain totals to
2.5" with local amounts to 5" are expected over the next several
hours.

Roth

ATTN...WFO...LZK...MEG...TSA...

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

LAT...LON   36159103 35519064 35179296 35299402 36029301