MESOSCALE PRECIPITATION DISCUSSION 0348
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
100 PM EDT TUE JUN 20 2017

AREAS AFFECTED...CENTRAL MS...CENTRAL AL...NORTH-CENTRAL
GA...WESTERN SC

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

VALID 201700Z - 202200Z

SUMMARY...VERY SLOW-MOVING THUNDERSTORMS WITH LOCALLY VERY INTENSE
RAINFALL RATES WILL BE EXPECTED THIS AFTERNOON. SOME FLASH
FLOODING WILL BE POSSIBLE GIVEN THE SLOW CELL MOTION.

DISCUSSION...SUFFICIENT BOUNDARY LAYER DESTABILIZATION HAS
OCCURRED TO SUPPORT A BROKEN AXIS HEAVY SHOWERS AND THUNDERSTORMS
ALONG A QUASI-STATIONARY FRONT WHICH EXTENDS FROM CENTRAL MS
EAST-NORTHEAST ACROSS CENTRAL AL...NORTH-CENTRAL GA AND WESTERN
SC. THE STEERING FLOW IS QUITE WEAK...WITH VERY WEAK PROPAGATION
VECTORS. MEANWHILE...THE COLUMN IS QUITE MOIST WITH PWATS
GENERALLY AROUND 2 INCHES. THE DEEP COLUMN OF MOISTURE WILL
CONTRIBUTE TO HIGHLY EFFICIENT RAINFALL PRODUCERS...WITH RAINFALL
RATES OF OVER 2 INCHES/HR...AND GIVEN THE VERY SLOW CELL
MOTION...SOME LOCALLY VERY HEAVY TOTALS WILL BE POSSIBLE THIS
AFTERNOON AS THE COVERAGE OF THUNDERSTORMS INCREASES.

THE SHEAR PROFILES ARE RATHER WEAK AND SUGGESTIVE THAT THE CELLS
WILL TEND TO REMAIN DISORGANIZED....BUT WITH COVERAGE LIKELY TO
EXPAND ALONG THE FRONT WITH ADDITIONAL DIABATIC HEATING AND THE
SLOW CELL MOTION...THERE WILL BE CONCERNS FOR SOME FLASH FLOODING.
THE LATEST HRRR/HRRRX GUIDANCE SUPPORTS AS MUCH AS 2 TO 4
INCHES...WITH ISOLATED HEAVIER AMOUNTS THROUGH ABOUT 22Z. WILL
CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...BMX...CAE...FFC...GSP...JAN...

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

LAT...LON   34488189 34158165 33668197 33358264 33218330
            32978467 32708672 32508817 32218943 32229015
            32529035 32948999 33468852 33728707 33788608
            33888514 34228377 34478283