MESOSCALE PRECIPITATION DISCUSSION 0058
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
211 AM EST FRI MAR 02 2018

AREAS AFFECTED...BURN SCARS OF SOUTHERN CA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 020710Z - 021510Z

SUMMARY...UPSLOPE FLOW NEAR AND AHEAD OF A  FRONTAL ZONE IS
EXPECTED TO LEAD TO HOURLY RAIN TOTALS TOWARDS 0.50" OVER THE NEXT
SEVERAL HOURS, WITH LOCAL AMOUNTS TO 2" POSSIBLE.

DISCUSSION...MODERATE TO HEAVY RAIN HAS BEEN SHIFTING DOWN THE CA
COAST NEAR A FRONTAL ZONE ACROSS PORTIONS OF CENTRAL CA.  RECENT
MESONET OBSERVATIONS SHOW HOURLY TOTALS OF 0.3-0.5" EAST OF
LIGGETT.  PRECIPITABLE WATER VALUES OF 0.6-0.7" LIE IN THIS AREA
PER RECENT GPS DATA.  VAD WIND PROFILES FROM SOUTHWEST CA SHOW 40
KTS OF SOUTHWEST INFLOW OFF THE PACIFIC.  SPC MESOANALYSES
ADVERTISE MU CAPE VALUES OF 100+ J/KG OFFSHORE SOUTHERN CA AHEAD
OF THE RAIN AREA NEAR THE CHANNEL ISLANDS.

PRECIPITABLE WATER VALUES ARE FORECAST TO RISE TO 0.75"+ OVER THE
NEXT SEVERAL HOURS AS THE FRONT PROGRESSES INTO THE AREA.  GFS
FORECASTS SUGGEST MINIMAL FRONTOGENESIS WITH THE BOUNDARY,
IMPLYING THAT ONSHORE FLOW/INSTABILITY WILL BE THE MAIN DRIVERS
FOR RAIN RATES.  THOSE QUANTITIES SUGGEST HOURLY RAIN TOTALS
PEAKING IN THE 0.4-0.5", WHICH IS HINTED AT IN THE 00Z HREF
PROBABILITIES AS WELL, MAXIMIZING AROUND 11Z.  COMPLICATING THE
PICTURE ARE RECENT BURN SCARS IN SOUTHERN CA WHICH WOULD BE HIGHLY
SUSCEPTIBLE TO ANY HEAVY RAINFALL.  THE MESOSCALE GUIDANCE
ADVERTISES LOCAL AMOUNTS OF 1.5-2" OVER THE SENSITIVE REGION,
WHICH WOULD BE PROBLEMATIC.  USED THE FLASH FLOOD POSSIBLE RATHER
THAN THE ATMOSPHERIC RIVER CATEGORY DUE TO THE BURN SCAR
SENSITIVITY.

ROTH

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

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

LAT...LON   35292089 35232016 34741871 34171792 34011819
            33981885 34151928 34311961 34422048 34592072
            34962068