MESOSCALE PRECIPITATION DISCUSSION 0522...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
503 PM EDT SUN SEP 27 2015
 
CORRECTED FOR TIME REFERENCE IN THE FINAL PARAGRAPH

AREAS AFFECTED...PORTIONS OF THE CENTRAL GULF COAST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 272100Z - 280100Z
 
SUMMARY...CONVECTION WITH HEAVY RAIN CONTINUES TO MOVE ACROSS THE
CENTRAL GULF COAST...WHICH COULD RESULT IN FLASH FLOODING.

DISCUSSION...KMOB RADAR SHOWED CONVECTION CONGEALING OVER SOUTHERN
MS/FAR SOUTHWEST AL AS THE 20 TO 25 KNOT LOW LEVEL EASTERLY INFLOW
OF 2.00+ PRECIPITABLE AIR (WHICH IS ABOUT TWO STANDARD DEVIATIONS
ABOVE THE MEAN) FEEDS CONTINUED DEVELOPMENT. KMOB RADAR ALSO
SHOWED AN INCREASING AREA OF 2-3 INCH PER HOUR RAINFALL RATES
ACROSS THIS SAME AREA. THESE ESTIMATES ARE SUPPORTED BY A ONE HOUR
RAINFALL OBSERVATION OF 2.50 INCHES AT KPQL.

THE IR LOOP SHOWED TOPS COOLING AGAIN AHEAD OF THE CLOSED MID
LEVEL LOW JUST SOUTH OF THE LA COAST. THE TRAJECTORY OF THE
CONVECTIVE CORE ON IR SUGGESTS THAT THE MAIN FLASH FLOOD THREAT
SHIFTS TO THE EAST ACROSS SOUTHERN MS AND FAR SOUTHWEST
AL/WESTERNMOST FL PANHANDLE INTO THE EARLY EVENING HOURS. 

THE 19Z HRRR IS THE MOST ROBUST WITH RAINFALL AMOUNTS ASSOCIATED
WITH THE CONVECTIVE CLUSTER...INDICATING THAT 3-5 INCHES IS
POSSIBLE ACROSS SOUTHERN MS AND FAR SOUTHWEST AL THROUGH 28/01Z.
OTHER HIGH RESOLUTION GUIDANCE (SUCH AS THE 12Z WRF ARW/NMMB) ARE
SLOWER WITH THE CONVECTION AND HIGHEST RAINFALL AMOUNTS...WHICH
CURRENT TRENDS DO NOT SUPPORT. GIVEN CURRENT RADAR
ESTIMATES...LOCAL 2-4 INCH RAINFALL AMOUNTS ARE POSSIBLE...AND
THESE AMOUNTS WOULD BE SUFFICIENT FOR FLASH FLOODING...ESPECIALLY
IN MORE URBAN AREAS.

AS THE CLUSTER MOVES FURTHER NORTH INTO SOUTHERN MS/SOUTHWEST
AL...IT BEGINS TO ENCOUNTER DRIER AIR...AND THE FLASH FLOOD THREAT
SHOULD START TO WANE AFTER 28/01Z.

HAYES

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

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

LAT...LON   32118888 32028852 31788804 31338782 30958769 
            30828770 30428754 30248762 30078796 29948832 
            29758866 29688882 29668901 29838924 30028939 
            30148957 30368977 30638986 30948990 31038995 
            31528985 31938948