MESOSCALE PRECIPITATION DISCUSSION 0238
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
952 PM EDT WED MAY 30 2018

AREAS AFFECTED...SOUTH-CENTRAL ALABAMA...SOUTH-CENTRAL MISSISSIPPI

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

VALID 310150Z - 310530Z

SUMMARY...SLOW-MOVING THUNDERSTORMS SHOULD PERSIST FOR AT LEAST A
COUPLE MORE HOURS THIS EVENING AND POSE A THREAT FOR FLASH
FLOODING. RAIN RATES APPROACHING 2 IN/HR AND THE POTENTIAL FOR
HEAVY RAIN DURATION OVER AN HOUR WOULD BE CAPABLE OF PRODUCING
FLASH FLOODING...PARTICULARLY IN AREAS THAT RECENTLY RECEIVED
HEAVY RAINFALL LAST NIGHT.

DISCUSSION...REGIONAL RADAR SHOWED SEVERAL ACTIVE CONVECTIVE
CLUSTERS AS OF 0130Z. ONE WAS A PERSISTENT LARGE CLUSTER JUST
NORTH OF KDYA IN WC AL...AND ANOTHER WAS A DEVELOPING CLUSTER OVER
SC MS JUST TO THE NORTH OF HATTIESBURG. RECENT TRENDS IN GOES-EAST
IR CLOUD TOP TEMPERATURES AND TOTAL LIGHTNING DO NOT SHOW RAPID
WEAKENING DESPITE THE LOSS OF DAYLIGHT...BUT A GENERAL WEAKENING
AND CONTRACTION OF CONVECTIVE COVERAGE IS EXPECTED AS THE BOUNDARY
LAYER BEGINS TO STABILIZE. HOWEVER...UNTIL THAT HAPPENS...THERE
WILL BE A THREAT OF FLASH FLOODING GIVEN RADAR ESTIMATED RAIN
RATES ALREADY ON THE ORDER OF 2 IN/HR AT TIMES.

THE CLUSTER OF STORMS JUST NORTH OF KDYA IS PROPAGATING ALONG THE
EDGE OF AN AREA THAT RECEIVED VERY HEAVY RAINFALL (2+ INCHES) IN
THE PAST 24 HOURS WITH SUBSTANTIALLY REDUCED FLASH-FLOOD GUIDANCE.
AS LONG AS THIS CLUSTER PERSISTS AND REMAINS RELATIVELY WIDE
(ABOUT 15 NM ALONG-TRACK AT THE MOMENT)...IT WOULD POSE THE THREAT
FOR AROUND AN HOUR OR MORE OF HEAVY RAINFALL AND FLASH FLOODING
GIVEN THE VERY WET ANTECEDENT CONDITIONS FROM AROUND 15 MILES
NORTH OF DEMOPOLIS AL TO NEAR MONTGOMERY AL.

THE CONVECTION IN SC MS IS SHOWING A PROPENSITY TO BACKBUILD AND
THUS REMAIN RELATIVELY STATIONARY FOR AROUND 40-80 MINUTES AT A
TIME...SUFFICIENT TO PRODUCE A QUICK 2-4 INCHES OF RAIN IN
LOCALIZED AREAS. CONTINUED NEW BURSTS OF LIGHTNING AND
OVERSHOOTING COLD CLOUD TOPS ON GOES-16 IR SATELLITE SUGGEST THAT
THIS BACKBUILDING PROCESS MAY CONTINUE FOR ANOTHER COUPLE HOURS IN
THE VICINITY OF A WEAK SURFACE TROUGH AND LOW-LEVEL CONVERGENCE
ZONE ANALYZED OBJECTIVELY BY THE RAP MODEL. GIVEN THE SIGNIFICANT
RAIN RATES AND STORM MOTIONS...LOCALIZED FLASH FLOODING WOULD ALSO
BE POSSIBLE IN THESE PORTIONS OF MISSISSIPPI.

LAMERS

ATTN...WFO...BMX...JAN...MOB...

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

LAT...LON   33278628 32868583 32188616 31618691 31318786
            31188889 31488989 31919030 32238972 32168880
            32918820 33238728