MESOSCALE PRECIPITATION DISCUSSION 0188
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
853 AM EDT WED MAY 23 2018

AREAS AFFECTED...SE ALABAMA...SW/WC GEORGIA

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

VALID 231252Z - 231730Z

SUMMARY...FLASH FLOODING WAS ONGOING AS OF 1230Z WITH A
SLOW-MOVING CLUSTER OF THUNDERSTORMS NEAR COLUMBUS GEORGIA. THIS
FLASH FLOODING WILL LIKELY CONTINUE AND COULD EXPAND EITHER AS THE
THUNDERSTORMS CONTINUE TO DRIFT SLOWLY SOUTH OR SOUTHEAST...OR AS
NEW STORMS DEVELOP TO THE SOUTHWEST. HOURLY RAIN RATES COULD
EXCEED 2 IN/HR.

DISCUSSION...KMXX AND KJGX RADARS SHOWED A PROMINENT CLUSTER OF
STORMS NEAR AND JUST EAST OF COLUMBUS GA THAT WAS CAUSING FLASH
FLOODING AS OF 1230Z (MULTIPLE FLASH FLOOD WARNINGS AND REPORTS
OVER THE PAST SEVERAL HOURS). OVER THE PAST 90 MINUTES THE
CENTROID OF THE CLUSTER HAS MOVED ONLY ABOUT 15-20 KM...WITH A
SLOW DRIFT TO THE S/SE. THESE RADARS ALSO SHOWED A WELL-DEFINED
SPIN IN THE MID-LEVELS ON THE NORTHEAST SIDE OF THE CONVECTIVE
CLUSTER...LIKELY AN MCV. THIS WAS CENTERED TO SOUTH OF A WEAK
SURFACE LOW...EVIDENT IN THE SURFACE WIND PATTERN ABOUT 20 MILES
EAST OF ATLANTA. THE RESULT IS BROADLY CONFLUENT LOW-LEVEL INFLOW
FROM THE WEST AND SOUTHWEST OVER CENTRAL AND SOUTHERN
ALABAMA...WHICH WAS ENABLING SOME BACKBUILDING OF THE CONVECTIVE
CLUSTER AND ENHANCING FLASH FLOOD POTENTIAL. THIS INFLOW REGION
WAS CHARACTERIZED BY RAP/HRRR ANALYZED CAPE AROUND 1000-1500 J/KG
AND PRECIPITABLE WATER VALUES AROUND 1.8 INCHES (PER CIRA BLENDED
TPW AND GPS-PW OBS).

ALTHOUGH IT IS APPROACHING THE TYPICAL DIURNAL MINIMUM FOR
CONVECTIVE INTENSITY...THE NEARLY UNCAPPED AND MODERATELY UNSTABLE
INFLOW REGION MAY BE ABLE TO SUSTAIN CONVECTION OVER THE NEXT FEW
HOURS WITH A CONTINUED FLASH FLOOD THREAT. AN INCREASE IN
CONVECTION ACROSS THE REGION WOULD BE MORE LIKELY AROUND 16-17Z
WITH CONTINUED INSOLATION... INCLUDING IN THE INFLOW REGION WHICH
MAY CAUSE THE FLASH FLOOD THREAT TO FURTHER EXPAND.

KMXX AND KJGX DUAL POL RAINFALL ESTIMATES HAVE APPROACHED OR
SLIGHTLY EXCEEDED 2 IN/HR AT TIMES...AS HAS THE MRMS RADAR
ANALYSIS. THESE SORT OF RATES CAN BE SUSTAINED IN THE VERY MOIST
AND UNSTABLE ENVIRONMENT PROVIDED CONTINUED SLOW MOTION OF THE
OVERALL CONVECTIVE CLUSTER AND A FAVORABLE SETUP FOR BACKBUILDING
AND NEW UPDRAFT GROWTH ON THE UPSHEAR (WESTERN) FLANK.

LAMERS

ATTN...WFO...BMX...FFC...MOB...TAE...

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

LAT...LON   33218356 32998299 32258313 31848383 31558484
            31458562 31588637 32118660 32538621 32688571
            32788500 33048449 33198411