MESOSCALE PRECIPITATION DISCUSSION 0154
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
951 AM EDT WED MAY 16 2018

AREAS AFFECTED...GEORGIA...WRN ALABAMA...FL PANHANDLE

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

VALID 161350Z - 161930Z

SUMMARY...SLOW MOVING RAIN BANDS AND THUNDERSTORMS ARE LIKELY
ACROSS PORTIONS OF ALABAMA... GEORGIA... AND THE FLORIDA PANHANDLE
TODAY. GIVEN THE ABUNDANT ATMOSPHERIC MOISTURE IN PLACE ACROSS THE
REGION... FLASH FLOODING WILL BE POSSIBLE WITH RAIN RATES REACHING
1-2 IN/HR AT TIMES.

DISCUSSION...REGIONAL RADAR MOSAIC AT 1330Z INDICATED AN ARC OF
VERY SLOW MOVING LOW-TOPPED CONVECTION STRETCHING FROM THE ATLANTA
METRO AREA INTO THE FLORIDA PANHANDLE. THIS WAS SITUATED RIGHT
ALONG A LOW-MID LEVEL DEFORMATION ZONE...EXTENDING NORTH-NORTHEAST
FROM AN APPROXIMATELY VERTICALLY STACKED LOW OVER THE FAR NORTHERN
GULF OF MEXICO. THIS DEFORMATION ZONE SHOULD PERSIST INTO THE
AFTERNOON HOURS IN THE PRESENCE OF SUBSTANTIAL ATMOSPHERIC
MOISTURE. THE 12Z SOUNDING FROM ATLANTA REPORTED A PRECIPITABLE
WATER VALUE OF 1.88 INCHES...AMONG THE HIGHEST VALUES REPORTED IN
MID MAY ON RECORD THERE. FURTHERMORE...LIMITED INSTABILITY IS
LIKELY KEEPING THE CONVECTION IN THIS CORRIDOR MORE LIMITED IN
VERTICAL EXTENT WITH COLLISION-COALESCENCE PROCESSES DOMINANT.
THIS WOULD FAVOR EFFICIENT RAINFALL PRODUCTION FROM ANY
SLOW-MOVING RAIN BANDS THAT CAN DEVELOP...AND 1+ IN/HR RAIN RATES
HAVE ALREADY BEEN REPORTED BY SOME SURFACE OBSERVING STATIONS.
GIVEN THE PERSISTENCE OF LOW-MID LEVEL FORCING IN A NEARLY
STATIONARY POSITION...AND THE OVERALL ENVIRONMENT...FLASH FLOODING
SEEMS POSSIBLE IN THE VICINITY OF THE DEFORMATION ZONE INTO THE
AFTERNOON.

FURTHER TO THE SOUTHEAST...NEAR THE FLORIDA BIG BEND AND
TALLAHASSEE AREA...ADDITIONAL CONVECTION IS ALSO LIKELY. GREATER
INSTABILITY IS FORECAST IN THIS AREA WHICH SEEMS MORE LIKELY GIVEN
THE BREAKS IN SOME OF THE CLOUD COVER IN THAT AREA. THE BIG BEND
REGION SHOULD ALSO STAY NEAR THE NOSE OF A LOW-LEVEL MOISTURE
TRANSPORT MAXIMUM TO THE EAST OF THE LOW OVER THE NORTHERN GULF.
THIS SHOULD FOCUS LOW-LEVEL FORCING IN THAT PARTICULAR AREA (IN
ADDITION TO SOME FRICTIONAL CONVERGENCE DUE TO ONSHORE FLOW FROM
THE GULF)...AND WITH INCREASING INSTABILITY SOME PERSISTENT
THUNDERSTORMS WILL BE POSSIBLE IN THE LATE MORNING AND AFTERNOON.
PRECIPITABLE WATER VALUES ARE ALSO FORECAST TO APPROACH 2 INCHES
IN THIS AREA...WHICH WOULD SUPPORT SOME HIGHER RAIN RATES (PERHAPS
REACHING AROUND 2 IN/HR) IF MORE ROBUST CLUSTERS OF STORMS OR
TRAINING OF CONVECTION CAN OCCUR. FLASH FLOOD GUIDANCE IS NOT
ESPECIALLY LOW IN THIS AREA...BUT 3-HR FFG AROUND 4 INCHES SEEMS
ACHIEVABLE IN THIS ENVIRONMENT.

LAMERS

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

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

LAT...LON   34358424 34068362 33708350 32958376 32028389
            31178350 30308291 29658312 29528375 29568438
            29458518 29988616 31108656 32268624 33168575
            33778516