MESOSCALE PRECIPITATION DISCUSSION 0180
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
216 AM EDT FRI MAY 06 2016
 
AREAS AFFECTED...COASTAL RANGES OF SOUTHERN CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 060615Z - 061500Z
 
SUMMARY...AN INVADING SHORTWAVE IS TAPPING INSTABILITY OFFSHORE
AND BRINGING THUNDERSTORM ACTIVITY INTO COASTAL SOUTHERN CA. 
HOURLY RAIN RATES UP TO 0.5" ARE POSSIBLE, WHICH COULD CAUSE
PROBLEMS IN BURN SCARS.

DISCUSSION...PER A RECENT SAB/NESDIS SATELLITE BRIEFING, WIDELY
SCATTERED THUNDERSTORMS ARE FORMING NEAR THE COAST OF SOUTHERN CA
WITH A LARGER CLUSTER LOOMING FARTHER OFFSHORE AHEAD OF A
SHORTWAVE ROTATING AROUND A CLOSED MID-LEVEL LOW.  PRECIPITABLE
WATER VALUES OF 0.87" EXIST NEAR THE COAST PER GPS VALUES, WHICH
IS 2+ SIGMAS ABOVE THE MEAN FOR EARLY MAY.  INFLOW AT 700 HPA IS
15-20 KTS OUT OF THE SOUTHWEST PER RAP FORECAST FIELDS AND VAD
WIND PROFILES.  SPC MESOANALYSES INDICATE 500-1000 J/KG MUCAPE
OFFSHORE THE COAST.  GUIDANCE SUGGESTS THAT MID-LEVEL LAPSE RATES
ACROSS THE REGION ARE STEEP DUE TO THE INVADING UPPER LOW.

THE EXPECTATION IS FOR THUNDERSTORM ACTIVITY TO MOVE SLOWLY INLAND
OVER THE NEXT SEVERAL HOURS, POSSIBLY BRINGING RAIN RATES UP TO
0.5".  THIS ACTIVITY IS EXPECTED TO BE PULSE IN NATURE WITH NO
SIGNIFICANT ORGANIZATION PER WEAK 850/700 HPA INFLOW AND 0-6 KM
BULK SHEAR VALUES AT OR BELOW 20 KTS.  THE 12Z MESOSCALE GUIDANCE
APPEARS TO HAVE A BETTER HANDLE ON THIS ACTIVITY THAN THE NEWER
00Z GUIDANCE, INDICATING A THREAT JUST INTO LOX'S COUNTY WARNING
AREA.  THE HIGHEST THREAT OF HEAVY RAINFALL APPEARS TO BE ACROSS
THE COASTAL RANGES WITHIN THE SOUTHERN PORTION OF THE SGX COUNTY
WARNING AREA FROM EAST OF TEMECULA TO SOUTHEAST OF RANCHO SAN
DIEGO.  THESE SORT OF RAIN RATES WOULD CAUSE PROBLEMS IN LOCATIONS
WITH BURN SCARS.  LOCAL AMOUNTS IN THE 1-2" RANGE ARE POSSIBLE
BETWEEN NOW AND 15Z.

ROTH

ATTN...WFO...LOX...PSR...SGX...

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

LAT...LON   34641823 34541740 34351664 33931662 33371618 
            33331650 33141640 33041621 32931631 32611599 
            32531659 32471691 33291723 33421756 33731847 
            34111891 34371883