MESOSCALE PRECIPITATION DISCUSSION 0663
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1001 PM EDT THU AUG 10 2017

AREAS AFFECTED...CENTRAL/NORTHERN AL...WESTERN GA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 110200Z - 110700Z

SUMMARY...VERY HEAVY RAIN FROM MERGING CLUSTERS OF SHOWERS AND
THUNDERSTORMS WILL CONTINUE OVER THE NEXT FEW HOURS. ADDITIONAL
FLASH FLOODING IS EXPECTED.

DISCUSSION...LATE-DAY VISIBLE SATELLITE IMAGERY WAS SHOWING
NUMEROUS CONVECTIVELY DRIVEN OUTFLOW BOUNDARIES THAT WERE
COLLIDING WITH EACH OTHER ACROSS CENTRAL AND NORTHERN AL ALONG
WITH PORTIONS OF WESTERN GA. THIS WAS RESULTING IN A NUMBER OF
STRONG CELL-MERGERS WHICH HAVE BEEN RESPONSIBLE FOR SOME VERY
HEAVY RAINFALL AMOUNTS THAT HAVE LOCALLY APPROACHED AND EXCEEDED 5
INCHES.

MORE RECENTLY...THE LATEST NON-OPERATIONAL GOES-16 IR DATA SHOWS
SOME ADDITIONAL STRONG COOLING OF CONVECTIVE TOPS OVER PARTS OF
NORTH-CENTRAL AND EAST-CENTRAL AL AND NOSING JUST BARELY INTO
WESTERN GA. THIS CONVECTION IS EMBEDDED WITHIN A DEEP TROPICAL
ENVIRONMENT WITH PWATS THAT ARE 2.25 TO 2.5 INCHES. THIS COUPLED
WITH THE HIGHLY CONCENTRATED NATURE OF THE MOISTURE THROUGH THE
COLUMN IS FAVORING RAINFALL RATES OF 4 INCHES/HR...AND SINCE THERE
ARE SEVERAL OVERSHOOTING TOPS AND CELL-MERGERS ONGOING...THE
RAINFALL RATES COULD EVEN BE A BIT HIGHER THAN THIS.

THE HIRES MODELS HAVE NOT BEEN DOING WELL WITH THIS CONVECTION ALL
EVENING...AND HAVE BEEN UNDER-DOING THE COVERAGE AND INTENSITY OF
CONVECTION. THE LATEST SATELLITE AND RADAR TRENDS SUPPORT A FEW
MORE HOURS OF STRONG CONVECTION...ESPECIALLY OVER AREAS OF
NORTH-CENTRAL TO EASTERN AL AND POSSIBLY STRETCHING A LITTLE MORE
INTO WESTERN GA. EXPECT ADDITIONAL RAINFALL AMOUNTS OF 3 TO 5
INCHES AT LEAST LOCALLY GIVEN THE HIGH RAINFALL RATES ENVIRONMENT
AND CONCERN OVER CELL-MERGERS. ADDITIONAL FLASH FLOODING IS LIKELY
THROUGH THE REMAINDER OF THE EVENING.

ORRISON

ATTN...WFO...BMX...FFC...HUN...TAE...

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

LAT...LON   35028632 34748534 34008433 33038393 32118415
            31928444 31828509 32078621 32638672 33518725
            33998768 34548753 34878718