MESOSCALE PRECIPITATION DISCUSSION 0056
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
339 PM EST THU MAR 01 2018

AREAS AFFECTED...CENTRAL/SOUTHERN CA COASTAL RANGES

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

VALID 012035Z - 020700Z

SUMMARY...HEAVY SHOWERS WILL CONTINUE TO ADVANCE SOUTH DOWN ACROSS
THE COASTAL RANGES OF CENTRAL TO SOUTHERN CA THIS AFTERNOON AND
THROUGH THE EVENING HOURS.

DISCUSSION...THE LATEST IR/WV SATELLITE IMAGERY SHOWS A DEEPENING
UPPER TROUGH ADVANCING SOUTH DOWN OFF THE WEST COAST WHICH IS
ALLOWING A COLD FRONT TO GRADUALLY SWEEP INLAND ACROSS NORTHERN
AND CENTRAL CA. THE LATEST AREA RADAR IMAGERY COUPLED WITH AN
OFFSHORE 1819Z AMSU PASS SHOWS NUMEROUS SHOWERS FOCUSING ALONG AND
JUST AHEAD OF THE BOUNDARY.

RAINFALL RATES HAVE OCCASIONALLY BEEN APPROACHING 0.50 INCH/HR
ALONG AND JUST INLAND OF THE COAST...AND THIS IS BEING AIDED BY A
MOIST SOUTHWEST LOW LEVEL JET OF NEAR 40 KTS WHICH IS ORIENTED
ORTHOGONAL TO THE COASTAL RANGES. PWATS ARE NOT PARTICULARLY HIGH
AS THE LATEST GOES-15 SOUNDER DATA ONLY SHOWS ABOUT 0.70 TO 0.80
INCH PWATS AIMING TOWARD THE COAST...BUT THE UPSLOPE
FLOW/OROGRAPHICS IS COMPENSATING BY ENHANCING THE RATES.

THE LATEST HIRES CAM GUIDANCE IS SUGGESTING SOME UPTICK THIS
AFTERNOON AND EVENING OF THE RAINFALL RATES FOR THE CENTRAL AND
EVENTUALLY SOUTHERN CA COASTAL RANGES AS 850 MB MOISTURE FLUX
ANOMALIES INCREASE TO 3 TO 3.5 STANDARD DEVIATIONS ABOVE NORMAL.
THIS COUPLED WITH THE DEGREE OF SURFACE FRONTAL
CONVERGENCE...UPSLOPE FLOW AND PROXIMITY OF FAVORABLE LEFT-EXIT
REGION UPPER JET DYNAMICS SHOULD FAVOR RAINFALL RATES THAT REACH
AS HIGH AS 0.60 TO 0.80 INCHES/HR.

THE HEAVIEST FOCUS OF RAIN INITIALLY WILL BE OVER SANTA CRUZ AND
SANTA CLARA COUNTIES...BUT THESE RAINS WILL SETTLE SOUTH DOWN
ACROSS MONTEREY COUNTY BY LATER THIS AFTERNOON...AND THEN AS FAR
SOUTH AS SAN LUIS OBISPO AND SANTA BARBARA COUNTIES THIS EVENING
AS THE LOW LEVEL ONSHORE FLOW INCREASES. A CONSENSUS OF THE 12Z
ARW/ARW-2 AND NMMB SOLUTIONS SUPPORT AS MUCH AS 3 TO 4 INCHES OF
RAIN THROUGH 06Z...WITH THE HEAVIEST TOTALS THIS PERIOD EXPECTED
TO BE ACROSS MONTEREY COUNTY. HOWEVER...AFTER 06Z THERE WILL BE
MORE OF A FOCUS OF HEAVIER RAIN FARTHER SOUTH AND CLOSER DOWN
TOWARD SANTA BARBARA COUNTY AS THE COLD FRONT SETTLES FARTHER DOWN
THE COAST AND INTERACTS WITH THE TRANSVERSE RANGES.

GIVEN THE EXPECTED RAINFALL...THERE WILL BE CONCERNS FOR RUNOFF
PROBLEMS AND POTENTIALLY SOME FLASH FLOODING NEAR THE BURN SCAR
AREAS. THIS WILL INCLUDE A THREAT OF DEBRIS FLOWS AS WELL. WILL
CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...HNX...LOX...MTR...STO...

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

LAT...LON   37672190 37362132 36592074 35782005 35121935
            34641906 34271920 34331947 34432047 34722094
            35492123 35912175 36452206 37002246 37522237