MESOSCALE PRECIPITATION DISCUSSION 0004
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
953 AM EST WED JAN 06 2016
 
AREAS AFFECTED...COASTAL RANGES OF CENTRAL & SOUTHERN CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 061453Z - 070223Z
 
SUMMARY...AN OCCLUDED CYCLONE IS EXPECTED TO LEAD TO HOURLY RAIN
RATES PEAKING WITHIN THE 0.5-0.75" RANGE, WITH LOCAL AMOUNTS OF 2"
POSSIBLE THROUGH 02Z WITHIN THE COASTAL RANGES OF CENTRAL AND
SOUTHERN CA.  HEAVY RAIN-RELATED ISSUES MOST LIKELY NEAR BURN
SCARS, URBAN AREAS, LOCATIONS SATURATED BY TUESDAY'S RAINFALL, AND
IN PLACES PRONE TO ROCK SLIDES.

DISCUSSION...THE LEADING EDGE OF AN OCCLUDED CYCLONE HAS PUSHED
INTO THE CENTRAL CA COAST THIS MORNING, WITH CONVECTION TRAILING
SOUTHWEST OFFSHORE SOUTHWEST CA.  HOURLY RAIN RATES APPROACHING
0.5" HAVE BEEN OBSERVED WITH THIS BAND WEST OF HERALDSBURG CA AND
EAST OF FREMONT CA PER MESONET OBSERVATIONS THIS MORNING. 
PRECIPITABLE WATER VALUES HAVE RISEN TO NEAR 0.8" PER GPS VALUES,
WITH SOUNDER-DERIVED VALUES JUST OVER AN INCH APPROACHING THE CA
COAST AS POINTED OUT IN AN EARLIER SAB/NESDIS BRIEFING.  INFLOW AT
850 HPA OF 45-50 KTS EXISTS IN ASSOCIATION WITH THIS SYSTEM PER
VAD WIND PROFILES AND RAP-BASED INITIALIZATION AND FORECAST
FIELDS.  MUCAPES OFFSHORE ARE > 500 J/KG PER RECENT SPC
MESOANALYSES.

SATELLITE IMAGERY REVEALS A LARGE AREA OF LOW-TOPPED CONVECTION
BETWEEN THE CA COAST BACK TOWARDS THE 136TH MERIDIAN AND AS FAR
NORTH AS THE 40TH PARALLEL BOOKMARKED BY A TRIO OF CIRCULATIONS
ALOFT, INDICATIVE OF MID-LEVEL INSTABILITY.  RAP FORECASTS
INDICATE THAT MUCAPES COULD BREACH 1000 J/KG OFFSHORE SOUTHERN CA,
WHICH COULD LEAD TO HIGHER RAINFALL RATES LATER TODAY.  THE CAM
GUIDANCE ADVERTISES THAT LOCAL AMOUNTS OF 2" ARE ANTICIPATED
DURING THIS HEAVY RAIN EVENT, WHICH SHOULD SHIFT FROM NORTHWEST TO
SOUTHEAST WITH TIME.  WHILE HOURLY RAIN RATES WOULD NORMALLY PEAK
NEAR 0.5" WITH THE TOTALS EXPECTED, THEY COULD RISE TOWARDS 0.75",
ALTHOUGH FOR A SHORT TIME FRAME, DUE TO THE FORECAST INSTABILITY. 
THE PEAK OF THE HEAVY RAIN EVENT IN SOUTHERN CA IS EXPECTED
BETWEEN 20-00Z PER THE 06Z SSEO NEIGHBORHOOD PROBABILITIES. 
AROUND 02Z, PRECIPITABLE WATER VALUES FALL TO BELOW 0.75"
REGIONALLY AS LOW-LEVEL INFLOW BEGINS TO DECREASE, SIGNALING THE
ENDING OF THE HEAVY RAIN EVENT.  THE MAIN ISSUES ARE EXPECTED IN
URBAN AREAS, NEAR BURN SCARS, LOCATIONS SUSCEPTIBLE TO ROCK
SLIDES, AND WITHIN ANY AREAS SATURATED BY YESTERDAY'S
PRECIPITATION.  

ROTH

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

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

LAT...LON   38252279 37972185 36832070 35291956 34821847 
            34511714 33951570 33231494 33441554 33991659 
            33801655 33411614 33351643 32881625 32571605 
            32351715 32691863 33311980 33892046 34992089 
            35952168 36512213 37532262 38042318