MESOSCALE PRECIPITATION DISCUSSION 0143
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
713 AM EDT THU APR 28 2016
 
AREAS AFFECTED...SOUTHEAST MS...SOUTHERN AL...WESTERN FL PANHANDLE 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 281108Z - 281600Z
 
SUMMARY...VERY INTENSE CLUSTER OF SHOWERS AND THUNDERSTORMS WITH
RAINFALL RATES APPROACHING 2.5 INCHES/HR WILL EXPAND IN COVERAGE
THIS MORNING AND MAY CAUSE SOME FLASH FLOODING.

DISCUSSION...IR SATELLITE IMAGERY HAS SHOWN THE RAPID EXPANSION OF
SOME COLD CONVECTIVE TOPS OVER SOUTHEAST MS OVER THE LAST COUPLE
OF HOURS WHICH APPEARS TO BE THE RESULT OF MODEST WARM ADVECTION
COUPLED WITH MODEST HEIGHT FALLS ASSOCIATED WITH A SHORTWAVE
DIGGING INTO THE SOUTHEAST U.S. EARLY THIS MORNING. AN 0814Z
AQUA-MODIS RGB AIRMASS PASS TENDED TO SUGGEST THIS AND WV IMAGERY
IMPLIES  SOME DEGREE OF DIVERGENT FLOW WHICH WOULD FOSTER SOME
LARGER SCALE ASCENT.

THE CONVECTION IS ALSO FOCUSING ALONG A WELL-DEFINED INSTABILITY
GRADIENT...WITH A NOSE OF MODERATE INSTABILITY POOLED NORTH FROM
THE NORTHERN GULF OF MEXICO AND INTO FAR SOUTHEAST MS AND SOUTHERN
AL. MLCAPE VALUES OF 2000 TO 2500 J/KG ARE NOTED ALONG WITH VERY
WEAK CINH. MEANWHILE...GPS-DERIVED PWATS ARE ON THE ORDER OF 1.5
TO 1.6 INCHES ACROSS THIS AREA AND THUS RAINFALL RATES ARE LIKELY
TO BE QUITE HIGH...AND ESPECIALLY GIVEN THE NOTED INSTABILITY AND
STRONG UPDRAFTS AS CONFIRMED BY A CLUSTER OF OVERSHOOTING TOPS AS
PER THE GOES-OTD ALGORITHM OVER HARRISON COUNTY MS.

THE 00Z ARW/00Z NMMB SOLUTIONS ALONG WITH THE 09Z HRRR ALL SHOW
CONVECTION CONCENTRATING THE NEXT COUPLE OF HOURS ACROSS SOUTHEAST
MS BEFORE THEN MOVING INTO SOUTHERN AL AND THE WESTERN FL
PANHANDLE. THE MEAN LAYER FLOW IS RELATIVELY WEAK FROM THE
W/SW...AND WITH RAINFALL RATES OF UP TO 2.5 INCHES/HR
EXPECTED...THERE MAY BE SOME VERY HEAVY RAINFALL TOTALS IN ONLY A
FEW HOURS. THE AFOREMENTIONED HIRES GUIDANCE SUGGESTS AS MUCH AS 3
TO 5 INCHES OF RAIN WITH LOCALLY HEAVIER AMOUNTS POSSIBLY
EXCEEDING 6 INCHES BY MIDDAY. THIS MAY RESULT IN SOME RUNOFF
PROBLEMS AND/OR FLASH FLOODING...WITH THE BIGGER CONCERN OVER
URBAN CENTERS.

ORRISON

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

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

LAT...LON   31778712 31658626 31138585 30458611 30328730 
            30218794 30198843 30228891 30328947 30608963 
            31098944 31538845