MESOSCALE PRECIPITATION DISCUSSION 0433
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
102 AM EST WED DEC 17 2014
 
AREAS AFFECTED...SRN CA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 170602Z - 171002Z
 
SUMMARY...SOUTHERN CALIFORNIA WILL SEE A 2 TO 3 HOUR WINDOW FOR
THUNDERSTORMS TO OCCUR AT POINTS ALONG THE PACIFIC COAST FROM SAN
SIMEON TO LOS ANGELES. BRIEF BUT INTENSE DOWNPOURS ON TOP OF
RECENT WET WEATHER MAY RESULT IN FLASH FLOODING...ESPECIALLY NEAR
BURN SCARS AND AREAS PRONE TO MUDSLIDES.

DISCUSSION...COLD MID LEVEL TEMPERATURES AND MODERATE TO STRONG
LAPSE RATES WERE FOSTERING DEEP CONVECTION AHEAD OF AN ADVANCING
COLD FRONT. THUNDERSTORMS OVER THE OCEAN WATERS HAD ALREADY SHOWN
AN ABILITY TO MOVE ONSHORE IN RECENT NIGHTS...AND THE HRRR
FORECASTS 500 TO AS MUCH AS 750 J/KG OF CAPE INTO THE EARLY
MORNING HOURS ALONG THE COAST AND INTO THE COASTAL MOUNTAIN RANGES.

AT 0550Z...THE KVBX DUAL-POL RADAR ESTIMATED GREATER THAN 1 INCH
PER HOUR RAIN RATES FROM ONE SWATH OF CONVECTION OFF THE WESTERN
SHORE OF SANTA BARBARA COUNTY. RAP SOUNDINGS SUGGEST A 2 TO 3 HOUR
WINDOW FOR CONVECTION TO OCCUR AT ANY GIVEN POINT ALONG THE COAST
BEFORE WINDS VEER AND LOW LEVEL WARM ADVECTION CEASES OR WEAKENS.
HIGH RESOLUTION MODEL GUIDANCE FROM 00Z IS FAIRLY UNIFORM IN
FORECASTING AREAL AVERAGE OF A HALF INCH OF RAIN OR MORE WITH
SMALL POCKETS OF ONE INCH. SOME OF THE RAIN MAY FALL OVER SHORT
PERIODS OF TIME...AND ALTHOUGH THE EVENT WILL BE PROGRESSIVE FROM
WEST TO EAST...RECENT RAINS MAY HAVE MADE THE SOILS MORE
SUSCEPTIBLE TO RAPID RUNOFF GIVEN THE BRIEF BUT UNUSUALLY HEAVY
RAIN RATES EXPECTED.

BURKE

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

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

LAT...LON   35782110 35632070 35292053 34851999 34581916 
            34661877 34591840 34391802 34231754 33861737 
            33651763 33611819 33811904 34241993 34562117 
            35602149