MESOSCALE PRECIPITATION DISCUSSION 0265
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
436 PM EDT MON AUG 11 2014
 
AREAS AFFECTED...EASTERN LA AND SOUTHWEST MS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 112035Z - 120035Z
 
SUMMARY...THUNDERSTORMS HAVE BEGUN TO TRAIN ALONG AN OUTFLOW
BOUNDARY STRETCHING FROM NORTHEAST LA INTO SOUTHWEST MS.  HOURLY
RAIN RATES OF 2.5" ARE POSSIBLE HERE, WHICH COULD CAUSE FLASH
FLOODING.

DISCUSSION...THUNDERSTORMS HAVE BEGUN TO TRAIN ACROSS NORTHEAST
LA, NEAR AND EAST OF A WEAK SURFACE LOW AND OUTFLOW BOUNDARY
MOVING INTO THE AREA FROM MS AND NEAR A DIFFLUENT SADDLE POINT IN
THE UPPER LEVEL WIND PATTERN.  PRECIPITABLE WATER VALUES OF AROUND
2.25" EXIST ACROSS THE REGION, WHICH LEADS TO THE POSSIBILITY OF
2.5" AN HOUR RAIN RATES, WHICH HAVE BEEN APPROACHED PER RADAR
ESTIMATES.  MOST UNSTABLE CAPES OF 3000-4000 J/KG LIE WITHIN THE
REGION, WHICH WOULD ARGUE FOR EVENTUAL FORWARD PROPAGATION,
TOWARDS THE SOUTHEAST AT 15-20 KTS.

THE EXPECTATION IS THAT THE THUNDERSTORM COMPLEX WILL CONTINUE
FEEDING OFF THE AVAILABLE MOISTURE AND INSTABILITY FOR ANOTHER
SEVERAL HOURS, THREATENING EASTERN LA AND SOUTHEAST MS WITH HEAVY
RAINFALL WHERE CELLS TRAIN.  THE OUTFLOW BOUNDARY SHOULD SHIFT
INTO SOUTHEAST LA BEFORE STALLING.  THE MESOSCALE GUIDANCE IS NOT
HANDLING CURRENT CONVECTIVE TRENDS IN THIS REGION, WITH THE 12Z
ARW, 12Z WRF NSSL, AND RECENT RUNS OF THE HRRR HAVING SOME
INDICATION OF THE EXISTENCE OF THE THUNDERSTORM COMPLEX.  A QUICK
2-4" IS POSSIBLE WHERE CELLS TRAIN, WHICH COULD LEAD TO FLASH
FLOODING IN AREAS WHERE SOILS WERE SATURATED BY YESTERDAY'S
THUNDERSTORM ACTIVITY.

ROTH

ATTN...WFO...JAN...LIX...LCH...SHV...

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

LAT...LON   30149030 30339126 31169242 32389307 32429184 31669070
            30859002 30149030