MESOSCALE PRECIPITATION DISCUSSION 0136
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
126 PM EDT THU APR 21 2016
 
AREAS AFFECTED...SOUTHWEST LA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 211725Z - 212025Z
 
SUMMARY...A POORLY MODELED LINE OF CONVECTION WITH HEAVY RAIN
RATES HAS BEEN MOVING TOWARDS THE REGION.  A QUICK 2-3", PERHAPS
IN ONE HOUR, COULD LEAD TO FLASH FLOOD CONCERNS OVER SATURATED
SOILS.

DISCUSSION...THE 12Z CAM GUIDANCE WAS MISSING THE BOAT CONCERNING
A PROGRESSIVE LINE OF CONVECTION MOVING THROUGH THE PINEY
WOODS/BIG THICKET OF EASTERN TX AHEAD OF A MID-LEVEL SHORTWAVE
LOCATED ALONG THE CENTRAL TX/OK BORDER.  THIS HAS MINIMIZED THE
USEFULNESS OF MASS FIELDS FROM THE RAP GUIDANCE.  INFLOW AT 850
HPA REMAINS ~25 KTS, IMPORTING MLCAPES OF 1000-1500 J/KG AND
PRECIPITABLE WATER VALUES OF 1.2-1.5" AHEAD OF THE LINE.  CELL
MERGERS HAVE BEEN THE MAIN HEAVY RAIN RISK SO FAR, AND RADAR
IMAGERY CONTINUES TO SHOW INDIVIDUAL THUNDERSTORMS FORMING AHEAD
OF THE LINE ADDING TO THE RAIN RATES THROUGH CELL MERGERS, WHICH
HAVE OCCASIONALLY REACHED 2.5" AN HOUR PER RADAR IMAGERY.

THE ORIENTATION OF THE INSTABILITY/MLCAPE IN THE GULF OF MEXICO
INDICATES THE ACTIVITY SHOULD TRACK SOMEWHAT MORE EASTERLY WITH
TIME ACROSS SOUTHWEST LA TO THE NORTH OF AN OUTFLOW BOUNDARY LEFT
OVER FROM EARLY MORNING CONVECTION.  THE LINE MOTION REMAINS ABOUT
30 KTS, SOMEWHAT QUICKER THAN FORWARD PROPAGATING CONVECTIVE
VECTORS INDICATE FOR ORGANIZED CONVECTION.  SO LONG AS CELL
MERGERS FROM NEW ACTIVITY AHEAD OF THE LINE CONTINUE, ALONG WITH
SHORT BOUTS OF CELL TRAINING, HOURLY RAIN RATES COULD OCCASIONALLY
REACH 2.5", WHICH WOULD PROVE TOO MUCH FOR SATURATED SOILS.  USED
A THREE HOUR HORIZON FOR THE MPD DUE TO FORECAST UNCERTAINTY. 

ROTH

ATTN...WFO...HGX...LCH...

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

LAT...LON   31169371 30899198 30149201 29489248 29659356 
            29339471 29369479 30189437