MESOSCALE PRECIPITATION DISCUSSION 175
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
804 PM EDT SUN APR 30 2017

AREAS AFFECTED...SOUTHEAST MS...SOUTHEAST LA...SOUTHERN
AL...WESTERN FL PANHANDLE

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

VALID 010003Z - 010403Z

SUMMARY...THUNDERSTORMS WITH HEAVY RAIN ARE EXPECTED TO CONTINUE
INTO THE LATE EVENING HOURS ACROSS THE CENTRAL GULF COAST REGION.
TRAINING CONVECTION FROM THE NORTHERN GULF OF MEXICO COULD RESULT
IN HOURLY RAIN RATES OF 1 TO 2 INCHES, AND IN COMBINATION WITH THE
EARLIER RAINFALL THIS AFTERNOON, FLASH FLOODING COULD BECOME A
PROBLEM FOR SOME AREAS.

DISCUSSION...THE LATEST DOPPLER RADAR TREND FROM 2200 TO 2345Z
INDICATES THAT THE CONVECTIVE LINE MOVING ACROSS SOUTHWEST ALABAMA
AND INTO THE WESTERN FLORIDA PANHANDLE HAS SLOWED DOWN SOME IN ITS
FORWARD PROGRESSION.  TRAINING CONVECTION IS NOW BECOMING MORE
LIKELY.  IN ADDITION, INTENSIFYING CONVECTION SOUTH OF THE
MISSISSIPPI COAST IS POISED TO MOVE INLAND ACROSS AREAS THAT HAVE
RECEIVED OVER AN INCH OF RAIN SINCE 20Z.  PRECIPITABLE WATER
VALUES OF 1.8 TO 2.2 INCHES ARE PRESENT OVER THIS REGION PER THE
SPC MESOANALYSIS.  INFLOW AT 850 HPA IS CONVERGENT WITH A LOW
LEVEL JET OF ABOUT 50 KTS, AND THIS IS FORECAST TO CONTINUE OVER
THE NEXT SEVERAL HOURS BASED ON THE LATEST RAP MODEL GUIDANCE.  AT
THE SURFACE, 75-DEGREE DEWPOINTS ARE FEEDING INTO THE CONVECTION
FROM THE SOUTHEAST, AND THIS WILL PROVIDE AMPLE FUEL FOR THE
CONVECTION TO CONTINUE.  BULK SHEAR IN THE 0-6 KM LAYER APPROACHES
40 KTS, WHICH HAS AT TIMES LED TO CONVECTIVE WAVES WITHIN THE
SQUALL LINE.

IN TERMS OF THE LATEST HI-RES GUIDANCE, THE HRRR AND THE
EXPERIMENTAL HRRR SUGGEST THAT THE HEAVIEST RAINFALL SHOULD BE
NEAR THE COAST THROUGH 4Z.  GIVEN THAT 1000-2000 J/KG OF MLCAPE IS
EXPECTED NEAR THE COAST AND LESSER AMOUNTS INLAND, THIS SCENARIO
SEEMS PLAUSIBLE.  EVEN THOUGH FLASH FLOOD GUIDANCE VALUES ARE
RELATIVELY HIGH RIGHT NOW, THE HIGHER RAINFALL RATES THAT ARE
EXPECTED COULD BE ENOUGH TO CAUSE SOME INSTANCES OF FLASH FLOODING.

HAMRICK

ATTN...WFO...BMX...JAN...LIX...MOB...TAE...

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

LAT...LON   32758632 32598517 31388521 30578579 30258639
            30118823 29808869 29428879 29068899 28928930
            29098965 29388986 29948984 31138914 31908848
            32548758