MESOSCALE PRECIPITATION DISCUSSION 0797
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
437 AM EST THU DEC 15 2016
 
AREAS AFFECTED...NORTHERN CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 151000Z - 151800Z
 
SUMMARY...ONSHORE MST FLUX SLOWLY DROPPING SOUTH ALONG N CA
COASTLINE WITH SOME MODERATE TO HEAVY RAINFALL CARRYING OVER  TO
THE NORTHERN SIERRAS THROUGH THE MORNING HOURS.   

DISCUSSION...SUBTLE WAVE/DUAL JET STRUCTURE SEEN IN GOES WV COMING
ASHORE CURRENTLY ACROSS EXT SW OR/NW CA WITH ENHANCED SHOWERS OVER
.5"/HR PER RECENT MESONET OBSERVATIONS IN DEL NORTE COUNTY AND
NEAR .7" SE OF CAPE MENDOCINO.  

AS THE WAVE LIFTS NORTHEASTWARD... INCREASED NORTHERLY FLOW SHOULD
ALLOW FOR THE FRONTAL ZONE/BEST LOW LEVEL MST FLUX AXIS TO DROP
SOUTH A BIT FASTER THAN THE LAST FEW HOURS.  CONSISTENT 45-60KT
85-7H FLOW AND TPWS BETWEEN 1.25-1.4" INDICATE FLUX RATES OF
150-170 UNITS WHICH IS AROUND 5 STANDARD DEVIATIONS ABOVE NORMAL
AND IN THE 99TH PERCENTILE; THIS SHOULD SUPPORT RATES AT OR JUST
BELOW .5"/HR ALONG THE COAST OF MENDOCINO COUNTY INTO SONOMA AND
EVENTUALLY MARIN COUNTIES NEARING 16-18Z. THOUGH RATES ARE HIGH
THE SOUTHWARD SHIFT SHOULD LIMIT TOTALS IN THE 2-3" RANGE PER
FAIRLY STRONG AGREEMENT IN RECENT HI-RES CAM GUIDANCE WITHIN SW
FACING OROGRAPHY.  

SUBTROPICAL CONNECTION AND LONG FETCH FROM SW SOURCE SUPPORTS
.3-.5" 7-5H PW VALUES PER CIRA LPW ANALYSIS...PROVIDING CONTINUED
STRONG OROGRAPHIC ASCENT ON LOWER SLOPES OF NORTHERN
SIERRAS...THIS ALONG WITH 20-30KT SOUTHERLY FLOW THROUGH THE
VALLEY WILL INCREASE MST CONVERGENCE AND INDUCE RATES IN EXCESS OF
.3" AND UP TO .5"/HR ACROSS SE SHASTA/E TEHAMA/W PLUMAS AND E
BUTTE COUNTIES FROM 12Z THROUGH 18Z.  THIS WILL BE OF INCREASED
CONCERN AS THE FRONTAL ZONE WILL CONTINUE TO SLOW AND THE NORTHERN
SIERRA REGION MAY ACT AS A MID-LEVEL PIVOT GIVEN THE UPSTREAM
HEIGHT FALLS APPROACHING FROM THE NORTH OFFSHORE WA/OR WILL
AMPLIFY THE ONSHORE FLOW FROM WSW TO SW TO SSW BY LATE MORNING
INTO THE EVENING. HI-RES GUIDANCE PARTICULARLY THE WRF-ARW AND
NSSL-WRF HAVE BEEN TRENDING THE BEST OVER THE PAST FEW HOURS
SUGGEST TOTALS OF 3-5" ARE POSSIBLE THROUGH 18Z WITH MORE EXPECTED
AFTERWARD.  GIVEN THIS POTENTIAL MAGNITUDE THROUGHOUT THURSDAY...
WPC WILL INTRODUCE A MODERATE RISK OF EXCESSIVE RAINFALL STARTING
AT 12Z TUES THROUGH 12Z WED. 

GALLINA

ATTN...WFO...EKA...MFR...MTR...STO...

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

LAT...LON   41922341 41362289 41342225 41532167 41072152 
            40512146 40102128 39712101 39352086 39232113 
            39272156 39602196 40022221 40492242 40352299 
            39662289 39062246 38712229 38282229 38032235 
            37992248 37822248 37922279 38172306 38542324 
            38792376 39172382 39422391 39622389 40002407 
            40182438 40702440 40932432 41492420 41842422