Mesoscale Precipitation Discussion 0656
NWS Weather Prediction Center College Park MD
133 AM EDT Tue Aug 14 2018

Areas affected...eastern OK into northwest AR/southwest MO

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

Valid 140531Z - 141120Z

SUMMARY...Training echoes of heavy rain are expected to develop
from eastern OK into northwestern AR over the next 1-3 hours. 3-6
inches of additional rainfall are expected through 11Z which is
expected to lead to flash flooding.

DISCUSSION...Radar imagery from 05Z showed an MCV over
northwestern AR with a backwards "C" shaped outflow boundary
evident across northwest AR. A region of stratiform precipitation
existed just west of the outflow over western AR with new
convective development across southeastern OK. This new
development was aligning with the low to mid level mean wind which
was unidirectional from the southwest at 20-30 kt. VAD wind plots
from KSRX sampled an axis of stronger 850 mb flow in the 30-35 kt
range, originating over TX, funneling in very high precipitable
water air of at least 2.0 to 2.1 inches per recent GPS
observations from northeastern TX into western AR. These observed
values were a bit lower than HRRR analyzed precipitable water
values along the OK/AR border of 2.25 to 2.5 inches, which may be
overinflating HRRR forecast QPF amounts through 12Z.

Nonetheless, there is a reservoir of MLCAPE across the eastern
TX/OK border into southwestern AR of 500-1000+ J/kg via the 05Z
SPC mesoanalysis which should help to support heavy rainfall rates
over the next few hours from eastern OK into northwestern AR.
Given the unidirectional flow from the southwest into the Boston
Mountains of the Ozark Plateau (upslope), training/slow moving
convection is expected to become more prevalent over the next few
hours with potential for 3-6 inches of rain by 11Z. The 00Z NSSL,
NAM_nest and past 4 runs of the HRRR support localized maxima in
excess of 7 inches, which could be overdone, but 3-6 inches seems
likely which could cause significant flash flooding across the
region.

Otto

ATTN...WFO...FWD...LZK...OUN...SGF...SHV...TSA...

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

LAT...LON   37319311 37039228 36299208 34449313 33789466
            33979599 35109621 36399520 37069420