MESOSCALE PRECIPITATION DISCUSSION 0132
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1111 AM EDT WED APR 20 2016
 
AREAS AFFECTED...WESTERN GULF COAST/LOWER MS VALLEY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 201515Z - 202115Z
 
SUMMARY...AN APPROACHING OUTFLOW BOUNDARY, INCREASING MOISTURE,
AND INCREASING INSTABILITY SHOULD ALLOW FOR INCREASING
THUNDERSTORMS COVERAGE.  CONVECTIVE MERGERS AND SHORT PERIODS OF
CELL TRAINING ARE POSSIBLE THIS AFTERNOON, WHICH COULD LEAD TO
FLASH FLOODING.

DISCUSSION...THE REMAINS OF A SQUALL LINE ARE LIMPING THROUGH
WESTERN AR, NORTHWEST LA, AND EASTERN TX AT THE PRESENT TIME. 
THIS OUTFLOW BOUNDARY IS LURING A DEW POINT GRADIENT/WEAK WARM
FRONT INTO SOUTHWEST LA.  PRECIPITABLE WATER VALUES OF ~1.5" LIE
WITHIN THE WARM SECTOR ALONG WITH MLCAPES OF 1000+ J/KG.  A PAIR
OF SHORTWAVES, ONE CONVECTIVE AND ONE WITHIN THE MAIN BELT OF THE
WESTERLIES, ARE APPROACHING THE REGION FROM THE WEST, ACTING TO
ENHANCE DIVERGENCE ALOFT.  INFLOW AT 850 HPA REMAINS NEAR 25 KTS.

THE CAM GUIDANCE SHOWS A SIGNAL FOR LOCAL 2-4" AMOUNTS WITHIN AN
AREA THAT SHOWS FAIRLY PERSISTENT 850 HPA CONVERGENCE.  WITH THE
LOW CLOUD DECK ACROSS PORTIONS OF LA TRYING TO MIX OUT/CONVECT PER
RECENT SATELLITE IMAGERY, INSTABILITY SHOULD BUILD NORTHEAST
TOWARDS WESTERN MS AND SOUTHEAST AR WITH TIME, WHICH IS ADVERTISED
BY THE RAP GUIDANCE.  LOW-LEVEL INFLOW COULD INCREASE SLIGHTLY
THIS AFTERNOON AS THE PAIR OF SHORTWAVES APPROACH.  FAIRLY
UNIDIRECTIONAL SOUTHWEST FLOW IMPLIES CELL TRAINING POSSIBILITIES,
WHILE DIFFERING VECTORS FOR THUNDERSTORM MOTION (NORTHEAST AT ~20
KTS FOR PULSE ACTIVITY AND EAST-SOUTHEAST AT ~10-15 KTS FOR
ORGANIZED CLUSTERS) HINT AT THE POSSIBILITY OF CELL MERGERS WITH
TIME, PARTICULARLY NEAR THE END OF THIS MPD'S WINDOW. HOURLY RAIN
RATES UP TO 1.75" ARE POSSIBLE WHERE CELLS MERGE AND/OR TRAIN.
WITH FLASH FLOOD GUIDANCE VALUES DEPRESSED FROM RECENT RAINFALL
WHICH HAS SATURATED AREA SOILS TO SOME DEGREE, FLASH FLOODING IS
CONSIDERED POSSIBLE.

ROTH

ATTN...WFO...HGX...JAN...LCH...LIX...LZK...MEG...SHV...

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

LAT...LON   34479092 34019035 31259109 29789186 29689236 
            30189359 30719507 31629417 32869305 33739210