MESOSCALE PRECIPITATION DISCUSSION 0662
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
329 AM EDT THU AUG 10 2017

AREAS AFFECTED...CENTRAL/NORTHEAST LA...EXTREME SOUTHEAST
AR...WEST-CENTRAL MS

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

VALID 100725Z - 101300Z

SUMMARY...HEAVY SHOWERS AND THUNDERSTORMS DEVELOPING OVER
NORTHEAST LA MAY BECOME A BIT BETTER ORGANIZED OVER THE NEXT FEW
HOURS ALONG WITH VERY HEAVY RAINFALL RATES. SOME FLASH FLOODING
CANNOT BE RULED OUT.

DISCUSSION...A LONG-LIVED MCV IS CURRENTLY FEATURED OVER
NORTH-CENTRAL LA AND IS DRIFTING GRADUALLY OFF TO THE NORTHEAST.
OVER THE LAST COUPLE OF HOURS THERE HAS BEEN SOME CONVECTIVE
DEVELOPMENT NEAR AND EAST OF THE VORT CENTER...AND CLOUD TOPS
CONTINUE TO COOL OVER WINN AND GRANT COUNTIES AS SEEN IN THE
NON-OPERATIONAL GOES-16 10.3 MICRON/IR IMAGERY. THE ACTIVITY IS
ALSO EMBEDDED WITHIN A MODEST INSTABILITY GRADIENT AND APPEARS TO
BE GETTING SOME SUPPORT FROM A SLOWLY STRENGTHENING WARM AIR
ADVECTION PATTERN OVER THE LOWER MS VALLEY THAT THE VORT IS
EMBEDDED WITHIN.

THE CONVECTION IS FOCUSING WITHIN A DEEP TROPICAL AIRMASS...WITH
PWATS OF 2.3 TO 2.5 INCHES AS PER LATEST GPS-DERIVED DATA...AND
THUS SOME VERY HEAVY RAINFALL IS UNDOUBTEDLY OCCURRING WITH THESE
CONVECTIVE CELLS THAT ARE GRADUALLY EXPANDING IN COVERAGE.
DUAL-POL ESTIMATES OVER THE PAST HOUR HAVE BEEN APPROACHING 2.5
INCHES/HR OVER NORTHEAST GRANT COUNTY AND THIS SEEMS REASONABLE
GIVEN THE PWAT ENVIRONMENT.

THE RECENT HRRR GUIDANCE HAS BEEN TRENDING TOWARD A SOMEWHAT MORE
ORGANIZED AND CONCENTRATED AREA OF CONVECTION THIS MORNING GOING
THROUGH THE 12Z TIME FRAME OVER NORTHEAST LA AND POSSIBLY GETTING
INTO PARTS OF WEST-CENTRAL MS TOWARD MID-MORNING AS THE VORT
CENTER LIFTS FARTHER TO THE NORTHEAST WITHIN INCREASING DEEP LAYER
SOUTHWEST FLOW.

THE 06Z HRRR IS FORECASTING AS MUCH AS 3 TO 6+ INCHES OF RAIN
THROUGH 12Z ACROSS PORTIONS OF NORTHEAST LA. THIS WILL DRIVE AT
LEAST SOME CONCERN FOR RUNOFF PROBLEMS AND FLASH FLOODING AND
ESPECIALLY IF ANY OF THESE RAINS IMPACT WEST-CENTRAL MS. SOME
AREAS WITHIN THE MPD THREAT AREA HAVE HAD HEAVY RAINFALL OVER THE
LAST COUPLE OF DAYS...AND SO THE ANTECEDENT CONDITIONS ARE LOCALLY
QUITE WET WHICH WILL ENCOURAGE THESE RUNOFF CONCERNS. WILL
CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...JAN...LCH...SHV...

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

LAT...LON   33239091 32669021 31759100 31469208 31479261
            31919303 32439292 33039216