MESOSCALE PRECIPITATION DISCUSSION 0182
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 PM EDT TUE MAY 22 2018

AREAS AFFECTED...ALABAMA...WRN GEORGIA...FLORIDA PANHANDLE

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

VALID 221757Z - 222300Z

SUMMARY...SHOWERS AND THUNDERSTORMS WILL MOVE SLOWLY IN THE
VICINITY OF A WEAK LOW IN CENTRAL ALABAMA...AND MAY PRODUCE
LOCALLY HEAVY RAINFALL AND FLASH FLOODING. RAIN RATES COULD
APPROACH 2 IN/HR.

DISCUSSION...ALTHOUGH THE SURFACE WIND FIELD AND PRESSURE PATTERN
ACROSS THE SOUTHEAST IS VERY WEAK...A BROAD CIRCULATION AND
RELATIVE MINIMUM IN PRESSURE APPEARED TO BE CENTERED NEAR
BIRMINGHAM. ANALYSIS OF THE LOW-LEVEL CLOUD BANDS WOULD ALSO PLACE
A CIRCULATION CENTER NEAR BHM...AND THUS IT IS LIKELY THAT A WEAK
LOW IS SITUATED OVER CENTRAL ALABAMA. SCATTERED CONVECTION HAD
DEVELOPED AS OF 1730Z AND WAS BECOMING MORE
NUMEROUS...PARTICULARLY TO THE SOUTH OF THE LOW WHERE LESS MORNING
CLOUD COVER HAD LIKELY CONTRIBUTED TO GREATER INSTABILITY.
ALTHOUGH THE CONVECTION WAS GENERALLY CELLULAR AND SCATTERED...A
COUPLE MESOSCALE BOUNDARIES MAY BE PROVIDING A BIT MORE
ORGANIZATION. THE FIRST WOULD BE THE SEA BREEZE...AND
THUNDERSTORMS WERE MORE NUMEROUS IN THE FLORIDA PANHANDLE ALONG
THIS BOUNDARY. THESE STORMS WERE SLOWLY LIFTING INLAND (TO THE
NORTH) AND MAY EVENTUALLY MAKE PROGRESS INTO SOUTHERN ALABAMA AND
SOUTHWEST GEORGIA. THERE ALSO APPEARED TO BE A WEAK SURFACE TROUGH
OR CONFLUENCE ZONE ARCING TO THE SOUTHWEST OF THE LOW NEAR THE
I-65 CORRIDOR. A MORE DEVELOPED BAND OF CLOUDS WAS SITUATED IN
THIS AREA AND SURFACE PRESSURES WERE SLIGHTLY LOWER THAN
SURROUNDING OBSERVATIONS.

AS THE LOW MOVES SLOWLY NORTH AND EAST...THE TROUGH TO ITS
SOUTHWEST MAY BEGIN TO PUSH INTO SOUTHEAST ALABAMA AND CONVERGE
WITH THE SEA BREEZE (OR THE COMPOSITE OUTFLOW BOUNDARY FROM
ASSOCIATED CONVECTION). THIS COULD PROVIDE A TEMPORARY 1-3 HR
FOCUS FOR GREATER CONVECTION IN SOUTHEAST ALABAMA AND SURROUNDING
AREAS. PARTS OF SOUTHEAST ALABAMA HAVE ALREADY EXPERIENCED HEAVY
RAINFALL IN THE PAST 24 HOURS...WITH RADAR ESTIMATES OF OVER 2
INCHES. THIS WOULD BE A POTENTIALLY FAVORED AREA FOR FLASH
FLOODING.

OVER MUCH OF THE OUTLINED AREA NEAR THE WEAK LOW IN CENTRAL
ALABAMA...THE LOW-MID LEVEL FLOW IS ALSO VERY WEAK AND RAP
ANALYSIS PLACES THE 850-300MB WIND SPEEDS LESS THAN 10 KNOTS. THIS
SHOULD ALLOW CONVECTION TO DRIFT SLOWLY. MANY AREA SHOULD CONTINUE
TO SEE A SCATTERING OF CONVECTION...WHICH WOULD NOT TEND TO FAVOR
FLASH FLOODING GIVEN THE LIMITED DURATION OF ASSOCIATED RAINFALL
AT ANY SPECIFIC LOCATION. HOWEVER...BROADLY CONFLUENT FLOW AROUND
THE LOW AND THE POSSIBILITY OF COLLIDING MESOSCALE BOUNDARIES MAY
PROMOTE SOME CELL MERGERS AND SUFFICIENT FOCUS TO PRODUCE A FEW
INCHES OF RAIN IN AN HOUR OR TWO. THIS COULD PRODUCE FLASH
FLOODING... ESPECIALLY IF IT WAS ALIGNED WITH AREAS THAT HAVE SEEN
HEAVY RAINFALL IN RECENT DAYS.

LAMERS

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

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

LAT...LON   34778625 34578557 34118484 33508425 32628393
            31808378 30848400 30268499 30608586 30618670
            30548769 31038763 31458712 32448672 32938680
            33698723 34488694