MESOSCALE PRECIPITATION DISCUSSION 0072
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1230 AM EST TUE MAR 07 2017

AREAS AFFECTED...CNTRL TO NERN AR AND THE MS VALLEY

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 070530Z - 071130Z

SUMMARY...TRAINING OF CELLS OUT AHEAD OF A PROGRESSIVE SQUALL LINE
MAY POSE A FLASH FLOOD THREAT OVER CNTRL AND NERN AR INTO THE MS
VALLEY WITH 3 HR RAINFALL RATES OF 2-3 INCHES POSSIBLE. THE FLASH
FLOOD THREAT IS EXPECTED TO DEVELOP BETWEEN 08-09Z.

DISCUSSION...REGIONAL RADAR IMAGERY AT 0515Z SHOWED THAT CLUSTERS
OF THUNDERSTORMS OVER THE OUACHITA MOUNTAINS ALONG THE OK/AR
BORDER HAVE BEEN MAINTAINING OR EXPANDING IN COVERAGE OVER THE
PAST HOUR. THESE STORMS ARE SITUATED WITHIN A MOIST AIRMASS
CONTAINING 1.2 TO 1.4 INCH PRECIPITABLE WATER VALUES AND AN
ESTIMATED MLCAPE OF 500-1500 J/KG PER RECENT SPC MESOANALYSES.
AVERAGE MOTIONS OF THESE LARGELY DISORGANIZED CELLS HAVE BEEN SWLY
AT ABOUT 30 KT...AND ESTIMATED INFLOW AT 850 MB IS A BIT S OF SW
AT 50-60 KT PER AREA VAD WIND PLOTS AND RAP ANALYSES.

THE EWD ADVANCEMENT OF A LARGE UPPER TROUGH LOCATED OVER THE CNTRL
PLAINS SHOULD ACT TO INCREASE UPPER LEVEL DIFFLUENCE OVER ERN
MO/AR THROUGH 09Z. IF STORMS CONTINUE TO GROW AND EXPAND IN
COVERAGE...THERE MAY BE TIME FOR EXCESSIVE RAINFALL RATES BEFORE
THE MAIN SQUALL LINE APPROACHES FROM THE NORTHWEST. AS THE SQUALL
LINE ADVANCES OVER THE NEXT 3-6 HOURS...SUBTLE VEERING OF 850 MB
FLOW WILL ALLOW BETTER ALIGNMENT WITH MEAN STORM MOTIONS PROMOTING
NARROW TRAINING AXES OF RAINFALL WITH RAINFALL RATES OF 1-1.5
IN/HR. WHILE SOME INCREASE IN CAPE IS POSSIBLE NEAR THE MS RIVER
OVER THE NEXT 3-6 HOURS GIVEN CONTINUED LOW LEVEL MOISTURE
ADVECTION...HIGHER CAPE VALUES ARE FORECAST TO REMAIN OVER WRN AR.
ADVECTION OF HIGHER CAPE TOWARD THE MS RIVER VALLEY MAY HELP
SUPPORT HIGHER RAINFALL RATES IN EXCESS OF THE 3 HOURLY FLASH
FLOOD GUIDANCE OF 2 TO 2.5 INCHES. THIS SCENARIO IS SUPPORTED BY A
HANDFUL OF 00Z HI-RES MODEL OUTPUT AND RECENT RUNS OF THE HRRR.

OTTO

ATTN...WFO...LZK...MEG...PAH...

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

LAT...LON   36398923 35928899 35298997 34369294 34339378
            34869406 35389327 35939170 36319024