MESOSCALE PRECIPITATION DISCUSSION 0039
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EST FRI MAR 04 2016
 
AREAS AFFECTED...CENTRAL CALIFORNIA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 041958Z - 050158Z
 
SUMMARY...EFFICIENT STRONG CONVECTION ACROSS CENTRAL VALLEY WILL
TRANSITION INTO LOWER SLOPES OF SIERRAS WITH INCREASING FLASH
FLOOD THREAT PARTICULARLY ACROSS INCREASING TERRAIN/BURN SCARS ON
LOWER SLOPES OF SIERRAS.

DISCUSSION...SATL IMAGERY INDICATES A MID-LEVEL VORT JUST WEST OF
THE MOUTH OF SAN FRANCISCO BAY LIFTING NORTHEAST PROVIDING DPVA
WITHIN A MODERATELY DIFFLUENT FLOW AT 3H TO SUPPORT ASCENT AOA THE
BAY VICINITY ATTM.  12Z OAK SOUNDING MODIFIED BY WEAK CAA ALOFT
FOR STEEPENING LAPSE RATES AS WELL AS SURFACE INSOLATION WITH
TEMPS IN THE CENTRAL VALLEY NEARING THE UPPER 70S WILL SUPPORT
INCREASING INSTABILITY OF 250-500 J/KG FOR INCREASED CONVECTIVE
GROWTH AS THE CELLS ADVANCE TOWARD THE VALLEY BY THE 20-21Z TIME
PERIOD.  ADDITIONALLY...INCREASED MID-LEVEL MOISTENING FROM 7H TO
5H PER CIRA LAYERED TPW WILL INCREASE TPWS OVER 1.0" TO NEAR 1.25"
BY 00Z AS WELL.  SURFACE-850MB MST IS ALREADY AVAILABLE WITH TDS
IN THE UPPER 50S-LOW 60S.  THIS WILL SUPPORT INCREASING EFFICIENT
RAINFALL PRODUCTION WITH DEEPER CELLS/CORES. EXPECTATION OF RATES
IN EXCESS OF .5"/HR LIKELY POSSIBLY AS HIGH AS 1.0"/HR WITH MOST
ROBUST/DEEP CONVECTION .  HOWEVER...GIVEN CONCERN IN THE OVERALL
DEPTH OF THE CONVECTIVE CORES DUE TO LIMITED
INSTABILITY/INCREASING CLOUD COVER TO REDUCE INSOLATION IN THE
SHORT TERM MIGHT LIMIT RATES...STILL WITH FFG VALUES LESS THAN
1.0/HR ISOLATED FF THREAT EXISTS IN THE VALLEY ITSELF.  

WITH TIME...THE OVERALL FLASH THREAT WILL INCREASE AS THE CELLS
REACH THE FOOTHILLS OF THE SIERRAS...DUE TO BURN SCARS AND
INCREASED OROGRAPHIC ASCENT.  THOUGH CELLS WILL MOVE QUICKLY
THROUGH THE FOOTHILLS AND WEAKEN...LOW LEVEL FLOW WILL VEER TO
SWLY AND INCREASE AOA 00Z TO 20-30KTS AT 850MB WITHIN CONTINUE
LARGER SCALE HEIGHT FALLS TO SUPPORT UPSTREAM REDEVELOPMENT AND
INCREASED MST FLUX AND MORE PERPENDICULAR OROGRAPHIC FLOW/ASCENT
PROVIDING A LONGER DURATION OF MORE MODERATE RAINS CAPABLE OF
EXTENDING THE FLOODING THREAT IN THE FOOTHILLS...AS WELL AS
EXPANDING THE THREAT INTO THE COASTAL RANGE SOUTH OF MONTERREY
BAY.  

GALLINA

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

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

LAT...LON   39552121 39372074 38762037 37981987 37552012 
            37022050 36632088 36252117 36092146 36182163 
            36382181 36762215 37232241 37792251 38062264 
            38652255 39122232 39432182