Mesoscale Precipitation Discussion 0666
NWS Weather Prediction Center College Park MD
942 AM EDT Wed Aug 15 2018

Areas affected...Eastern OK and Western AR

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

Valid 151341Z - 151941Z

SUMMARY...Flash flooding becoming increasingly likely through the
morning hours across portions of eastern Oklahoma and western
Arkansas.

DISCUSSION...An area of convection continues to stream eastward
across eastern Oklahoma into western Arkansas. This activity is
developing ahead of a well defined mid level shortwave moving
across central Oklahoma...as noted by the robust drying in the mid
level water vapor imagery. There also appears to be a smaller
scale MCV embedded within the broader shortwave trough...evident
on radar approaching the Oklahoma/Arkansas border at 13z. Both of
these features will continue to provide deep layer ascent...along
with enhanced southwesterly low level flow to their south and
east. This enhanced flow is maintaining a persistent axis of low
level moisture transport into Oklahoma and Arkansas.

Recent MRMS rainfall rate trends do show a gradual broadening and
enhancement of hourly totals across the area. IR satellite shows
some brief pulses of colder cloud tops...but have yet to see an
expansion and maintenance of colder cloud tops. Thus still a bit
unclear how widespread the excessive rainfall amounts will be.
With that said, the extended duration of favorable mid/upper level
dynamics and low level moisture transport, supports a continuation
of showers and embedded heavier convective cores into at least the
early afternoon hours ahead of the slow moving shortwave trough
axis.

Recent runs of the HRRR continue to depict localized 3-6" rainfall
amounts into early afternoon...and is in pretty close agreement to
some of the 06z HREF guidance. This system does have a history of
producing small scale excessive rainfall amounts...most recently
near Oklahoma City and across far southeast Kansas. Thus while
widespread extreme rainfall amounts may not necessarily
occur...smaller scale 5"+ amounts appear probable. Given this
potential, and locally heavy antecedent rainfall over the area,
some flooding and flash flood concerns appear likely into the
afternoon hours.

Chenard

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

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

LAT...LON   36029385 35919313 35619282 34979304 34679411
            34749492 34919555 35159573 35529570 35749541
            35889473 35999431