MESOSCALE PRECIPITATION DISCUSSION 0435
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
411 PM EST TUE DEC 23 2014
 
AREAS AFFECTED...CENTRAL AND SOUTHEAST LA...CENTRAL AND SOUTHERN
MS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 232100Z - 240100Z
 
SUMMARY...NUMEROUS BANDS OF HEAVY SHOWERS AND THUNDERSTORMS TO
PERSIST THROUGH EARLY EVENING HOURS. REPEATING CONVECTION WILL
FOSTER SOME RISK FOR FLASH FLOODING.

DISCUSSION...A STRONG SHORTWAVE TROUGH IS DIGGING ACROSS THE
SOUTHERN PLAINS AND IS NOW BEGINNING TO MOVE TOWARD THE LOWER MS
VALLEY. THIS IS DRIVING A COLD FRONT TO THE EAST...AND THE LATEST
SURFACE OBSERVATIONS INDICATE AN AREA OF LOW PRESSURE DEVELOPING
ALONG THE FRONT NEAR THE MS/LA BORDER. MEANWHILE...STRONG UPPER
LEVEL JET DYNAMICS IS FAVORING A BROAD AREA OF ENHANCED LARGE
SCALE ASCENT DOWNSTREAM ACROSS THE GULF COAST STATES...AND WITH AN
AREA OF STRONG WARM ADVECTION BEING ENHANCED BY A 50 TO 60 KNOT
LOW LEVEL JET.

THIS LARGER SCALE FORCING/SHEAR ENVIRONMENT COUPLED WITH
IMPRESSIVE MOISTURE TRANSPORT IS FOSTERING WIDESPREAD AREAS OF
HEAVY SHOWERS AND THUNDERSTORMS AS DENOTED BY IR SAT AND RADAR
IMAGERY. THE CONVECTION IS GENERALLY ORIENTED IN BANDS SW/NE
ACROSS CENTRAL/SOUTHERN LA NORTHEAST INTO CENTRAL/SOUTHERN MS
AHEAD A COLD FRONT. RAINFALL RATES WITHIN THE BANDS ARE ON THE
ORDER OF 1 TO 2 INCHES/HR...AND WITH SOME SHORT-TERM CONCERN FOR
THESE CONVECTIVE BANDS TO TRAIN OVER THE SAME AREA...THERE WILL BE
A RISK FOR SOME FLASH FLOODING.

THE HI-RES 12Z ARW AND LAST FEW RUNS OF THE HRRR SUGGEST THE
POTENTIAL ADDITIONAL RAINFALL AMOUNTS OF 2 TO 4 INCHES OVER
PORTIONS OF THE THREAT AREA...AND THIS COUPLED WITH THE FACT THAT
CLOUD TOPS ARE COOLING AND THERE HAVE BEEN NUMEROUS OVERSHOOTING
TOPS OVER THE LAST COUPLE OF HOURS...SUGGESTS THE THREAT FOR FLASH
FLOODING MAY INCREASE.

ORRISON

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

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

LAT...LON   32568896 32208845 31578872 30518943 29659040 
            29349121 29329161 29519187 30059191 30819104 
            31659016 32278960