MESOSCALE PRECIPITATION DISCUSSION 0440
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
951 AM EST SAT DEC 27 2014
 
AREAS AFFECTED...SOUTHERN LA...SOUTHERN MS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 271450Z - 272000Z
 
SUMMARY...VERY HEAVY RAINFALL RATES ASSOCIATED WITH A CLUSTER OF
THUNDERSTORMS IS EXPECTED TO PRODUCE SOME POTENTIAL FOR FLASH
FLOODING THE NEXT FEW HOURS.

DISCUSSION...IR SAT IMAGERY SHOWS A CLUSTER OF INCREASINGLY
COLD-TOPPED CONVECTION MOVING INLAND ACROSS PORTIONS OF SOUTHERN
LA. THE CONVECTION IS FORMING ALONG THE LEADING EDGE OF A DEEPER
PLUME OF HIGH PWATS EMBEDDED WITHIN A BROAD WARM AIR ADVECTION
REGIME. COORDINATION WITH NESDIS/SAB SUGGESTS THE PWATS ARE ON THE
ORDER OF 1.75 TO 2 INCHES JUST OFFSHORE OVER THE NORTHWEST GULF OF
MEXICO...AND THIS IS CONFIRMED BY THE LATEST MICROWAVE/AMSU PWAT
IMAGERY AND GOES-SOUNDER DATA WHICH SHOWS THIS POOL OF DEEPER
MOISTURE SLOWLY SHIFTING NORTH. 

THE CONVECTIVE ACTIVITY WHICH IS ELEVATED IN NATURE AS PER 12Z
RAOB DATA IS BEING AIDED BY THE PRESENCE OF A LOW LEVEL COASTAL
FRONT THAT IS SLOWLY LIFTING NORTH AS WELL. ON THE LARGER
SCALE...THERE IS A POSITIVELY TILTED UPPER TROUGH SLOWLY MOVING
EAST ACROSS THE CENTRAL/SOUTHERN PLAINS...HOWEVER THERE IS A
WELL-DEFINED AXIS OF H25 RRQ JET DYNAMICS FOCUSED OVER MUCH OF THE
LOWER MS VALLEY WHICH IS PROGGED TO STRENGTHEN FURTHER TODAY AND
THIS WILL FOSTER AN INCREASE IN LARGER SCALE ASCENT.

THE HIRES MODELS LED PREDOMINANTLY BY THE 00Z NSSL-WRF STRONGLY
SUGGEST AN INCREASE IN ORGANIZED CONVECTION OVER PORTIONS OF
SOUTHERN LA THIS MORNING AND DEVELOPING SW/NE IN A BANDED FASHION
OVER INTO SOUTHERN MS AFTER 18Z. THE INCREASE IN LARGER SCALE
FORCING COUPLED WITH DEEPER LAYER MOISTURE/INSTABILITY FOCUSING
ALONG THE COASTAL FRONT SUPPORTS THE NSSL-WRF OUTPUT. RAINFALL
RATES OF 2 TO 3 INCHES/HR WITHIN THE COLDEST CONVECTIVE TOPS ALONG
WITH SOME POTENTIAL FOR LOCALIZED TRAINING SUGGESTS FLASH FLOODING
WILL BE POSSIBLE THROUGH LATE MORNING AND EARLY AFTERNOON AS THIS
CONVECTION EVOLVES.

ORRISON

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

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

LAT...LON   31488958 31388882 30958875 30638913 30199054 
            29589140 29589202 29949211 30709145 31209061 
            
¡