MESOSCALE PRECIPITATION DISCUSSION 0580
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
655 PM EDT FRI OCT 16 2015
 
AREAS AFFECTED...PORTIONS OF SOUTHERN CA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 162255Z - 170350Z
 
SUMMARY...SCATTERED CONVECTION DEVELOPING IN A HIGH MOISTURE
CONTENT ENVIRONMENT COULD PRODUCE FLASH FLOODING IN AREAS WITH
SATURATED SOILS INTO THE EARLY EVENING.

DISCUSSION...CONVECTION IS FIRING OVER PORTIONS OF LOS
ANGELES...VENTURA AND SANTA BARBARA COUNTIES AS THE CIN IS ERASED.
MLCAPE VALUES OF 1000-1500 J/KG ARE EXPANDING ACROSS THIS PORTION
OF SOUTHERN CA...AND THIS SHOULD CONTINUE TO FEED DEVELOPING
SCATTERED CONVECTION. THE SPC MESOANALYSIS SHOWED PRECIPITABLE
WATER VALUES OF 1.30 INCHES IN PLACE (WHICH IS ABOUT FOUR STANDARD
DEVIATIONS ABOVE THE MEAN). DEVELOPING STORMS ARE ALREADY CAPABLE
OF PRODUCING FLASH FLOODING...ESPECIALLY IN AREAS THAT RECEIVED
HEAVY RAINFALL THU.

THERE IS A WINDOW OF DESTABILIZATION THROUGH ABOUT 17/03Z...DURING
WHICH TIME CONVECTIVE COVERAGE IS EXPECTED TO INCREASE. THE CLOSED
MID LEVEL LOW HAS MOVED INLAND OVER SOUTHERN CA...AND THE
SLACKENING MID LEVEL FLOW SHOULD RESULT IN SLOW STORM MOTIONS
THROUGH THIS EVENING. THE COMBINATION OF SLOW STORM MOTION AND
HIGH MOISTURE CONTENT AIR WILL RESULT IN THE THREAT FOR FLASH
FLOODING... EVEN IF THE CONVECTION REMAINS SCATTERED IN NATURE.

THERE IS A FAIRLY STRONG HIGH RESOLUTION MODEL GUIDANCE SIGNATURE
(SUPPORTED BY THE LATEST HRRR...12Z WRF-ARW/NMMB AND 12Z NSSL WRF)
FOR AS MUCH AS 2 INCHES OF RAINFALL IN SLOW MOVING CONVECTION
THROUGH 17/03Z... MAINLY OVER LOS ANGELES...VENTURA AND SANTA
BARBARA COUNTIES. CONSIDERING THE FLASH FLOODING ISSUES THU...ANY
ADDITIONAL HEAVY RAINFALL COULD RESULT IN FLASH FLOODING. 

INSTABILITY SHOULD BEGIN TO DIMINISH AFTER 17/03Z...AS SEEN IN THE
LATEST HIGH RESOLUTION GUIDANCE SUITE. THE THREAT FOR FLASH
FLOODING SHOULD BE REDUCED BY THE LATE EVENING HOURS.

HAYES/DEMUTH

ATTN...WFO...HNX...LOX...MTR...SGX...VEF...

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

LAT...LON   36132044 35911992 35691964 35561952 35541947 
            35291790 34751735 34031721 33931807 34001872 
            34091928 34421997 34472000 35072044 35352069 
            35742082 35992081