MESOSCALE PRECIPITATION DISCUSSION 4
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
352 AM EST WED JAN 4 2017
 
AREAS AFFECTED...CENTRAL CALIFORNIA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 040851Z - 042051Z
 
SUMMARY...A LONG DURATION HEAVY PRECIPITATION EVENT WITH LOWER
ELEVATION HEAVY RAINFALL IS UNDERWAY ACROSS CENTRAL CALIFORNIA. 
MULTIPLE ROUNDS OF MODERATE TO OCCASIONALLY HEAVY RAIN WILL LIKELY
RESULT IN SOME AREAS RECEIVING 3 TO 5 INCHES OF RAIN BY EARLY
AFTERNOON WITH HOURLY RATES UP TO A HALF INCH POSSIBLE.

DISCUSSION...A STEADY STREAM OF MOISTURE FLOWING INLAND FROM THE
PACIFIC IS EXPECTED TO CONTINUE THROUGH 21Z FOR MUCH OF CENTRAL
CALIFORNIA.  A PROLONGED FETCH OF 30 TO 40 KNOT 850MB FLOW
ORIENTED ORTHOGONAL TO THE TERRAIN, ALONG WITH PWS ON THE ORDER OF
1.0 TO 1.3 INCHES, IS SETTING THE STAGE FOR ENHANCED RAINFALL. 
THE HEAVIEST RAINFALL TOTALS ARE EXPECTED FOR THE COASTAL
MOUNTAINS SOUTH OF SAN FRANCISCO, AND THE WESTERN SLOPES OF THE
CENTRAL SIERRA NEVADA BELOW ABOUT 5000 FEET.  SOME ELEVATED
INSTABILITY MAY ALLOW FOR PERIODS OF HEAVIER CONVECTIVE ACTIVITY
CAPABLE OF PRODUCING RAINFALL RATES APPROACHING ONE INCH PER HOUR.
 THE PLACES WITH GREATEST RUN-OFF CONCERNS WOULD BE RECENT
BURN-SCAR AREAS AND THOSE LOCATIONS THAT RECEIVED APPRECIABLE
RAINFALL ON TUESDAY.

THE LATEST HRRR AND HRRR EXPERIMENTAL GUIDANCE SUGGESTS 12-HOUR
TOTAL RAINFALL AMOUNTS ON THE ORDER OF 2 TO 4 INCHES FOR THE
OROGRAPHICALLY ENHANCED AREAS, AND GENERALLY UNDER AN INCH FOR THE
CENTRAL VALLEY.  THIS IS EXPECTED AS DEEPER MOISTURE FROM THE
SOUTHERN STREAM IS ADVECTED TOWARDS THE COAST AND ALLOWS FOR
HIGHER RAINFALL RATES AND MORE EFFICIENT PRECIPITATION PROCESSES. 
ADDITIONAL RAINFALL IS EXPECTED BEYOND THIS PERIOD.

HAMRICK

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

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

LAT...LON   40112121 39992095 39102059 38462037 37671978 
            37111933 36861904 36361887 36301923 36362003 
            36202041 35862051 35302030 35062066 35432113 
            35892159 36242200 36902238 37462271 37882246 
            38172179 38682138 39222142 39742148