MESOSCALE PRECIPITATION DISCUSSION 0163
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
701 AM EDT SUN JUN 29 2014
 
AREAS AFFECTED...AR, NORTHERN MS, SOUTHWEST TN, NORTHWEST AL 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 291101Z - 291701Z
 
SUMMARY...HEAVY RAINFALL ASSOCIATED WITH A STEADY-STATE CONVECTIVE
COMPLEX CONTINUES TO PRODUCE RAINFALL RATES OF AROUND 2.5" AN
HOUR.  WHEN COMBINED WITH PREVIOUS RAINS AND MODEST FLASH FLOOD
GUIDANCE VALUES, NUMEROUS OCCURRENCES OF FLASH FLOODING ARE
ANTICIPATED.

DISCUSSION...A LENGTHENING/BROADENING HEAVY RAIN BAND EXTENDS FROM
NORTH CENTRAL AR EASTWARD ACROSS THE WESTERN MS/TN BORDER.  THE
THUNDERSTORMS ARE LOCATED NEAR AND BEHIND AN OUTFLOW BOUNDARY,
WHICH HAS SHOWN SLIGHT NORTHEAST MOTION OVER THE PAST SEVERAL
HOURS. A RAINFALL REPORT FROM HOWELL AR OF 6.70" WAS RECENTLY
RECEIVED FROM THE LZK/LITTLE ROCK AR WEATHER FORECAST OFFICE.
INFLOW AT 850 HPA INTO THE REGION IS 40 KTS, DOUBLE THE MEAN
850-400 HPA WINDS, WHILE CAPES TO THE SOUTH ARE 1000-3000 J/KG. 
CORFIDI VECTORS OPPOSE THE LOW-LEVEL INFLOW, IMPLYING BACKBUILDING
IS POSSIBLE, WHICH HAS BEEN SEEN WITH THE AR ACTIVITY THIS
MORNING.  WHEN COMBINED WITH PRECIPITABLE WATER VALUES OF 2-2.5",
ABOVE THE 95TH PERCENTILE FOR LATE JUNE, THE CRITERIA FOR THE WET
MULTI-CELL ENVIRONMENT HAVE BEEN MET.

THE EXPECTATION IS FOR THE BAND TO CONTINUE LENGTHENING EASTWARD,
DESPITE EVIDENCE TO THE CONTRARY IN MESOSCALE GUIDANCE QPF FIELDS
-- ONLY THE LATEST RUN OF THE HRRR EXTENDS THE HEAVY RAINS AS FAR
EAST AS THE SHARED AL/MS/TN BORDER.  MASS FIELDS FROM THE RECENT
RUNS OF THE RAP AND ARW INDICATE THAT THE BAND COULD LENGTHEN TO
THE THREE-STATE BORDER WITH TIME.  RAINFALL RATES UP TO 2.5" AN
HOUR REMAIN POSSIBLE WITHIN THIS REGION.  WHILE 850 HPA SLOWLY
WEAKENS, IT REMAINS 25 KTS AND NEARLY DOUBLE THE 850-400 HPA MEAN
WIND AS LATE AT 18Z, IMPLYING THAT THE THUNDERSTORM AREA COULD
CONTINUE PRODUCING HEAVY RAINFALL THROUGH THE MORNING HOURS
POTENTIALLY INTO NORTHWEST AL.  THERMAL CONTRAST SHOULD INCREASE
ALONG THE OUTFLOW BOUNDARY DURING THE MORNING HOURS, WHICH COULD
AID SURFACE-BASED CONVERGENCE.  A QUICK 3-6" OF ADDITIONAL
RAINFALL IS LOCALLY POSSIBLE OVER THE NEXT SEVERAL HOURS, WHICH
SHOULD LEAD TO NUMEROUS INSTANCES OF FLASH FLOODING.

ROTH

ATTN...WFO...OHX...HUN...MEG...LZK...

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

LAT...LON   35378724 34928700 34498738 34508920 34709069 35209201
            35939291 36219189 36089011 35728846 35378724