MESOSCALE PRECIPITATION DISCUSSION 0013
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1019 PM EDT THU MAR 12 2015
 
AREAS AFFECTED...SOUTHEASTERN LA/SOUTHERN MS... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 130218Z - 130618Z
 
SUMMARY...AN INCREASED THREAT FOR HEAVY RAINFALL EXISTS DURING THE
NEXT SEVERAL HOURS ACROSS SOUTHEASTERN LA AND EXTENDING INTO
EXTREME SOUTHERN MS. HIGHER-END FFG VALUES SUGGEST ANY FLASH
FLOODING WILL LIKELY BE LOCALIZED.

DISCUSSION...AN IMPRESSIVE BATCH OF CONVECTION HAS DEVELOPED
ACROSS THE NORTH-CENTRAL GULF OF MX WITH AN INCREASING NUMBER OF
CG LIGHTNING STRIKES IN THE PAST HOUR. ALL OF THIS IS OCCURRING
ALONG AN ENHANCED AXIS OF TROPOSPHERIC MOISTURE EXTENDING DOWN
INTO THE YUCATAN. 00Z RAOBS ACROSS THE REGION SHOWED 1.50 INCH AND
ABOVE PWATS ADVECTING NORTHWARD WITH THE KLIX SOUNDING SUGGESTING
PWATS APPROACHING THE 99TH PERCENTILE FOR MARCH. FURTHER...THIS
00Z SOUNDING INDICATED A NEARLY SATURATED ATMOSPHERE UP TO ~300 MB
WITH A TALL/SKINNY CAPE PROFILE. ADJACENT THERMODYNAMIC PROFILES
SUPPORT THE FACT THE INSTABILITY HAS MOVED WELL INLAND.

CURRENTLY A WELL-DEFINED LLJ WAS IN PLACE ACROSS THE SCALLOPED
REGION WITH 30 TO 40 KNOTS OF INFLOW OFF THE GULF OF MX. THE 01Z
RAP IS QUITE SUPPORTIVE OF MAINTAINING THE STRENGTH OF THIS LLJ
THROUGHOUT THE OVERNIGHT HOURS. THE INSTABILITY ALSO SEEMS TO
PERSIST AS MIXED-LAYER CAPE VALUES REACH THE 500-1000 J/KG RANGE
ACROSS SOUTHEASTERN LA. THIS APPEARS TO BE MORE THAN ENOUGH TO
SUSTAIN CONVECTION GIVEN THE STRONG VERTICAL MOTIONS IN THE WARM
SECTOR COUPLED WITH SUFFICIENT UPPER-LEVEL DIFFLUENCE. THE BIGGEST
QUESTION IN THE HIGH-RESOLUTION MODELS IS REGARDING HOW FAR NORTH
THE CONVECTION WILL MIGRATE. MOST OF THESE MODELS SEEM TO LOWER
RAINFALL AMOUNTS ACROSS WEST-CENTRAL MS WHERE THE INSTABILITY CUTS
OFF. OVERALL...PER COORDINATION WITH WFO LIX...HOURLY RAINFALL
RATES OF 0.75 TO 1.25 INCHES ARE POSSIBLE WITH THE INCOMING BAND
WHICH MAY LEAD TO PONDING OVER AREAS WITH SATURATED GROUNDS. WILL
REASSESS THE SITUATION AS NEW 00Z GUIDANCE ARRIVES.


RUBIN-OSTER

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

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

LAT...LON   31148975 30718905 29708879 28668911 28208988 
            28489087 29299146 30299138 31009070