MESOSCALE PRECIPITATION DISCUSSION 0799
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
948 PM EST THU DEC 15 2016
 
AREAS AFFECTED...COASTAL CENTRAL AND SOUTHERN CA...CENTRAL AND
SOUTHERN CA SIERRAS 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 160300Z - 161500Z
 
SUMMARY...CONTINUED STRONG AND DEEPLY MOIST SWLY ONSHORE FLOW
SUPPORT HOURLY RATES AROUND .5"/HR.  FLASH FLOODING/DEBRIS FLOWS
ARE POSSIBLE WITHIN BURN SCARS AND URBAN CENTERS. 

DISCUSSION...GOES-W WV LOOP DENOTES THE RAGGED REMAINS OF
SHORTWAVE NEAR 34N135W WITH BROAD BAROCLINIC SHIELD DOWNSTREAM
ACROSS CENTRAL CA ENTERING THE BROAD ENTRANCE REGION OF 130KT
POLAR JET THAT REMAINS WELL DISPLACED ACROSS OR/ID/MT
ATTM...CONTINUING TO PROVIDE MODEST ASCENT ACROSS THE SIERRAS. 
STILL THE MAIN DRIVER OF HEAVY RAINFALL ACROSS THE COASTAL RANGES
OF CENTRAL CA AND AGAIN ACROSS THE THE MID-SLOPES OF THE SIERRAS
CONTINUES TO BE THE DEEP MST FLUX FROM NEARLY UNIDIRECTIONAL LOW
LEVEL FLOW WITH 40-50KTS OF FLOW AND TPWS IN THE RANGE OF
1.25...WITH SOME ISOLATED POCKETS ALONG THE FRONT WHERE SFC MST
CONVERGENCE IS MAXIMIZED WITH VALUES TO 1.4".  THIS WILL CONTINUE
TO SUPPORT RATES IN EXCESS OF .5"/HR ALONG THE CENTRAL AND
SOUTHERN SIERRAS THROUGH TO ABOUT 12Z AS THE FOCUS/FRONT REACHES
THE SOUTHERN SIERRAS AND THE CHANNEL ISLANDS.  ISOLATED HOURLY
RATES OF .75"/HR ARE NOT OUT OF THE REALM OF POSSIBILITY
PARTICULARLY ACROSS THE SANTA LUCIA RANGE FROM 05-07Z AS THE FRONT
DESCENDS.  HI-RES CAMS CONTINUE TO BE IN FAIRLY SOLID AGREEMENT
WITH THE HRRR/WRF-ARW/WRF-NMMB AND NSSL-WRF SUGGESTING 2-3" ALONG
THE COASTAL RANGE AND UP TO 4-6" IN THE FRESNO AND TULARE
MID-SLOPES OF THE SIERRAS THROUGH 15Z. 

SOUTHERN COASTAL CALIFORNIA (SE OF POINT CONCEPTION)... FURTHEST
SOUTH TROPICAL CONNECTION PLUME HAS A WEAK INFLECTION EMBEDDED
WITHIN IT NEARING THE WESTERN CHANNEL ISLANDS PER RAP ANALYSIS AND
IR...TPWS OVER 1.5" ARE OBSERVED VIA SATELLITE SENSORS WITH LITTLE
CONTAMINATION WITH 45-50 KT OF SWLY 850MB FLOW FOCUSED ON THE
CHANNEL ISLANDS AND E SANTA BARBARA/W VENTURA COUNTY OVER THE NEXT
HOUR OR TWO WITH INCREASED RATES JUST BELOW .5"/HR LIKELY FOR THE
TRANSVERSE RANGES PARTICULARLY SW FACING OROGRAPHICS. THE POSITIVE
IS THE DURATION OF THESE .3-.5"/HR RATES SHOULD BE LIMITED TO AN
HOUR OR SO AS INSTABILITY IS LACKING (MUCAPES BELOW 100 J/KG). 
STILL THE RATES AND TOTALS OF 1-1.5" SHOULD BE SUFFICIENT FOR
FF/DEBRIS FLOWS IN BURN SCARS.  AS THE MAIN POLAR FRONT DESCENDS
SOUTH DEEPEST MOISTURE AND FORCING WILL BE REDUCING WITH LIGHTER
RATES UP TO .25" (MAINLY IN FAVORED SW AND WEST FACING TERRAIN)
LINGERING THROUGH 14-15Z...LEADING TO AN ADDITIONAL .25-.75" BUT
LESSENING FLOODING THREAT/IMPACT.  

GALLINA

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

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

LAT...LON   39022029 37761934 36331813 35131849 34751826 
            34321712 33571676 33531753 33991867 34301983 
            34422052 34732083 35172097 35482126 35732149 
            36142195 36392205 36702203 36992228 37242238 
            37382213 37452159 37202120 36782083 36242050 
            35642008 35131917 35501907 36201944 36761983 
            37112016 37652054 38052074 38282083 38752091 
            38882083