MESOSCALE PRECIPITATION DISCUSSION 0762
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
753 PM EDT TUE AUG 29 2017

AREAS AFFECTED...COASTAL MS...AL AND WESTERN FL PANHANDLE

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

VALID 300000Z - 300600Z

SUMMARY...ISOLATED THREAT FOR FLASH FLOODING WITH SLOW SUPERCELLS
MOVING ASHORE WITH INCREASING COVERAGE/THREAT TOWARD 06Z.

DISCUSSION...GOES-16 WV SUITE AND CIRA LAYERED PW LOOP DENOTE
PINCHING OF THE WARM CONVEYOR BELT ACROSS THE CENTRAL GULF
GENERALLY SOUTH OF 28N MAINLY AS THE EASTERLY FLOW AIR ENCROCHES
THROUGH THE SOUTHEASTERN GULF.  LONGER DURATION BLENDED TPW LOOPS
ALSO DENOTE THE NARROWING AND SLOW REDUCTION OF MOISTURE WITHIN
THE BELT DECREASING FROM THE BAY OF CAMPECHE NORTHWARD WITH TIME. 
AS SUCH DRY AIR ENTRAINMENT HAS SUPPORTED SLIGHTLY STRONGER
OUTFLOW BOUNDARIES/ROLL CLOUDS ACROSS THE CENTRAL
GULF...PROPAGATING THE LEADING EDGE OF THE DEEPER MOISTURE A BIT
FURTHER EAST AS NOTED BY THE DEEP CONVECTIVE BURST SOUTH OF PANAMA
CITY, FL.  THIS LEADING EDGE IS ALSO INTERACTING WITH DRAPED
FRONTAL BOUNDARY THAT EXTENDS FROM THE CHANDELEUR ISLANDS EASTWARD
TO ABOUT 87W BEFORE ANGLING SE TOWARD TAMPA BAY.

SSWLY SFC TO 7H FLOW IN THE WARM CONVEYOR HAS BEEN ISENTROPICALLY
ASCENDING ACROSS THE FRONT INITIATING CONVECTION...AND GIVEN
PROXIMITY TO THE BOUNDARY SOMETIMES SUPERCELLUAR IN NATURE SLOWING
NORTHWARD PROGRESSION AND INCREASING DURATION OF HIGHLY EFFICIENT
WARM CLOUD RAIN PROCESSES. IT IS WITH THESE BACKBUILDING
SUPERCELLS THAT RAIN RATES OVER 2.5"/HR AND TOTALS OVER 3-5" ARE
POSSIBLE SUCH AS THOSE OVER MOBILE COUNTY AND SOUTHWARD ALONG THE
WESTERN EDGE OF THE WARM CONVEYOR.

GIVEN THE INCREASED BREATH OF THE PLUME FURTHER NORTH ACROSS THE
NORTH CENTRAL GULF (DUE TO FASTER EASTWARD PROPAGATION OF THE
LEADING EDGE)...THE LLJ IS LESS FOCUSED AT THIS TIME (MORE SO
FURTHER EAST INTO FL PANHANDLE) AND CELLS HAVE BEEN MORE SCATTERED
IN NATURE.  HOWEVER ISOLATED LOCATIONS WITH REPEAT
TRACKS/BACKBUILDING OR SLOW SUPERCELLS MAY LEAD TO FLASH FLOODING
THOUGH IS ONLY CONSIDERED POSSIBLE AT THIS TIME GIVEN THE HIGHER
FFG VALUES.

TOWARD 06Z THOUGH THE NORTHWARD ADVANCEMENT OF THE FRONTAL ZONE
COMBINED WITH THE ENHANCED FRICTIONAL SFC CONVERGENCE SHOULD
STRONGLY INCREASE THREAT FOR CONVECTIVE COVERAGE AND STORM
INTENSITY MAINLY FOCUSED IN COASTAL COUNTIES FROM MOBILE BAY TO
CHOCTAWHATCHEE BAY...WITH GREATER RISK FOR FF AFTER 06Z AS
SUGGESTED BY THE RECENT RAP/HRRR AND ESRL HRRRV3. (NOTE ARW MAY BE
ON RIGHT TRACK IN MAGNITUDE/COVERAGE BUT A BIT TOO FAST ADVANCING
THE FRONT NORTH). WILL CONTINUE TO MONITOR FOR ANY NECESSARY
UPDATES.    

GALLINA

ATTN...WFO...LIX...MOB...TAE...

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

LAT...LON   31418754 31258626 30318504 29958476 29498514
            30148678 30008768 29668838 29538897 30148945
            30478962 30788953 30918899 31258845