MESOSCALE PRECIPITATION DISCUSSION 0029
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1131 AM EST FRI JAN 20 2017
 
AREAS AFFECTED...CNTRL TO SRN CA COAST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 201630Z - 202230Z
 
SUMMARY...A FLASH FLOOD AND FLOOD THREAT WILL CONTINUE TO AFFECT
THE CNTRL AND SRN CA COASTAL REGIONS THROUGH 22Z. SHORT TERM BUT
HIGH RAINFALL RATES OF 1-2 INCHES IN 3 HOURS ARE EXPECTED.

DISCUSSION...LOOPS OF WATER VAPOR IMAGERY OVER THE PAST FEW HOURS
HAVE SHOWN A REGION OF ROBUST DARKENING MOVING INTO THE CNTRL CA
COAST COINCIDENT WITH THE LEADING EDGE OF A STRONG UPPER LEVEL
JET...WITH 150 KTS NOTED ON THE 12Z VBG SOUNDING BETWEEN 200 AND
250 MB. THE SOUNDING ALSO SHOWED SSWLY FLOW OF 60 KTS AROUND 800
MB AND PRECIPITABLE WATER NEAR 0.8 INCHES. THE STRONG LOW LEVEL
FLOW AND POWERFUL JET DYNAMICS ARE HELPING TO OVERCOME ONLY MODEST
MOISTURE ANOMALIES OF +1 TO +2 STANDARD DEVIATIONS ABOVE THE MEAN.
15Z SURFACE OBSERVATIONS PLACED A COLD FRONT JUST PAST MONTEREY
BAY WITH SEVERAL FLASH FLOOD WARNINGS JUST NORTH AND SOUTH OF THE
SAN FRANCISCO BAY AREA. 

AS THE COLD FRONT CONTINUES TO STEADILY PROGRESS DOWN THE CA
COASTLINE TODAY...PRECIPITABLE WATER VALUES ARE EXPECTED TO REMAIN
STEADY AHEAD OF THE BOUNDARY UNTIL 20-21Z AT WHICH POINT MAXIMUM
VALUES ARE FORECAST BY RECENT RUNS OF THE RAP TO BE WITHIN A TENTH
OF AN INCH OF 1.0 INCHES FOR SRN LOS ANGELES AND ORANGE
COUNTIES...ALLOWING FOR SLIGHTLY INCREASED INTEGRATED VAPOR
TRANSPORT INTO SRN CA. FORECAST MUCAPE IS EXPECTED TO REMAIN
LOW...UP TO ABOUT 250 J/KG...BUT SUPPORTIVE OF THUNDERSTORMS WITH
RAINFALL RATES OF 0.75 TO 1 IN/HR GIVEN ADDED LIFT TIED TO THE
LEFT EXIT REGION OF THE AFOREMENTIONED JET AS IT SLIDES DOWN THE
CA COASTLINE THROUGHOUT THE DAY. 

GIVEN THE WELL ABOVE AVERAGE RAINFALL OVER THE PAST 2 WEEKS NORTH
OF POINT CONCEPTION AND THE POTENTIAL FOR SHORT TERM BUT INTENSE
RAINFALL RATES ALONG MOST OF THE CNTRL/SRN CA COASTLINE...FLASH
FLOODING AND FLOODING ARE POSSIBLE.

OTTO

ATTN...WFO...HNX...LOX...MTR...SGX...

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

LAT...LON   36152144 36072132 35802108 35662089 35552051 
            35422020 35081975 34801922 34741863 34501787 
            34421716 34121667 32721636 32631647 32641721 
            33201754 33611833 33981896 34171952 34362016 
            34372048 34782089 35122105 35402111 35622124 
            35822144 36062151