MESOSCALE PRECIPITATION DISCUSSION 0576
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
929 PM EDT THU OCT 15 2015
 
AREAS AFFECTED... PORTIONS OF SOUTH CENTRAL CA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 160130Z - 160500Z
 
SUMMARY...CONVECTION FIRING ALONG A SURFACE TROUGH TAPS HIGH
MOISTURE CONTENT AIR TO PRODUCE A THREAT FOR FLASH FLOODING.

DISCUSSION...CONVECTION CONTINUES TO FIRE ALONG A SURFACE TROUGH
EXTENDING ACROSS PORTIONS OF SOUTH CENTRAL CA...IN AN AXIS OF 1000
J/KG MLCAPE AND 1.20 TO 1.40 INCH PRECIPITABLE WATER AIR (WHICH IS
ABOUT FOUR STANDARD DEVIATIONS ABOVE THE MEAN). CIN IS BEGINNING
TO ERODE THE INSTABILITY OVER THE TERRAIN...AND MUCH OF THE
MOISTURE AND INSTABILITY IS BEING TRANSPORTED INTO THE VALLEY. 

THE STORMS HAVE A HISTORY OF PRODUCING FLASH FLOODING OVER
PORTIONS OF LOS ANGELES AND VENTURA COUNTIES. THE INSTABILITY
SHOULD BEGIN TO WANE WITH THE LOSS OF HEATING...SO THE OVERALL
COVERAGE OF CONVECTION SHOULD DIMINISH WITH TIME. HOWEVER...THE
EXISTING CONVECTION COULD PRODUCE LOCAL 2+ INCH RAINFALL
AMOUNTS...ESPECIALLY ALONG A SURFACE TROUGH EXTENDING ACROSS THE
VALLEY. 

THESE AMOUNTS ARE WELL SUPPORTED BY THE LATEST HIGH RESOLUTION
GUIDANCE (INCLUDING THE LATEST HRRR...AS WELL AS THE 12Z WRF-ARW
AND WRF-NMMB). FLASH FLOOD GUIDANCE VALUES ARE GENERALLY AROUND AN
INCH...AND LOCAL CELL TRAINING (AS MID LEVEL WINDS LINE UP WITH
CORFIDI VECTORS...PROMOTING REPEAT CONEVCTION) COULD EASILY
PRODUCE RAINFALL AMOUNTS IN EXCESS OF FLASH FLOOD GUIDANCE VALUES.

AN OVERALL DOWNWARD TREND IN CONVECTION AND FLASH FLOOD POTENTIAL
IS EXPECTED TOWARD 16/05Z...AS THE REMAINING INSTABILITY IS
EXHAUSTED AND INHIBITION INCREASES.

HAYES

ATTN...WFO...HNX...LOX...MTR...

ATTN...RFC...CNRFC...

LAT...LON   37632002 37481976 37261951 36951916 36661886 
            36131841 35751807 35481785 35211765 34951770 
            34821774 34781791 34801810 34861834 34871836 
            34871839 35001902 35091938 35311971 35491999 
            35622010 35842028 36092040 36192035 36692035 
            36832036 37102050 37422052 37602042