MESOSCALE PRECIPITATION DISCUSSION 0069
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
955 AM EST THU MAR 10 2016
 
AREAS AFFECTED...NORTHERN CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 101454Z - 110254Z
 
SUMMARY...ATMOSPHERIC RIVER WITH CONTINUED MODERATE TO LOCALLY
HEAVY RAINFALL...

DISCUSSION...AN ATMOSPHERIC RIVER OF MOISTURE CONTINUES TO BE
POINTED INTO NORTHERN CA THIS MORNING. VWP AND RAP FORECASTS SHOW
40-45 KTS OF SOUTHWESTERLY FLOW ENHANCING PRECIPITATION RATES IN
THE FAVORED TERRAIN LOCATIONS. AN INTERESTING SETUP THIS
MORNING...WITH TWO DISTINCT PLUMES OF UPPER LEVEL MOISTURE SEEN ON
WATER VAPOR IMAGERY. THE SOUTHERN PLUME IS ACTUALLY THE AXIS OF
BEST MOISTURE TRANSPORT AND HIGHEST PRECIPITABLE WATER...WITH
ORIGINS TO THE TROPICAL PACIFIC SOUTH OF HI. THE NORTHERN
PLUME...WHICH HAS RECENTLY BEGUN TO BLOSSOM APPEARS TO BE
ASSOCIATED WITH INCREASED UPPER FORCING AS THE SHORTWAVE WELL
OFFSHORE CONTINUES TO DIG...INCREASING SYNOPTIC SCALE ASCENT AHEAD
OF IT. WATER VAPOR IMAGERY SHOWS A CONNECTION BETWEEN THESE TWO
PLUMES...WHICH IS LIKELY THE INTERSECTION OF THE ATMOSPHERIC RIVER
WITH THE INCREASED LARGE SCALE FORCING.

THE PLUME OF MOISTURE WILL CONTINUE TO SHIFT SOUTH...BUT AT A SLOW
PACE...BEFORE BECOMING NEARLY STATIONARY NEAR SAN FRANCISCO.
PRECIPITABLE WATER VALUES WITHIN THE PLUME DO NOT CHANGE MUCH
THROUGH THE DAY...LIKELY REMAINING NEAR OR ABOVE THE 98TH
PERCENTILE FOR THIS TIME OF YEAR. HOWEVER DO EXPECT LOW LEVEL FLOW
TO DECREASE LATER THIS MORNING INTO THIS AFTERNOON AS THE LOW OVER
SOUTEHRN CANADA WEAKENS AND THE FRONT BEGINS TO WASH OUT. THUS THE
SOLUTIONS SUGGESTED BY THE HRRR/EXPERIMENTAL HRRR AND RAP SEEM TO
MAKE SENSE. SUGGESTING RAINFALL RATES OF 0.25"-0.5" (LOCALLY AS
HIGH AS 0.75") WILL CONTINUE WITHIN THE PRECIPITATION AREA AS IT
SLOWLY SHIFTS SOUTH THROUGH AROUND 21Z...WITH RATES ON THE
DECREASE AFTER THAT AS FLOW WEAKENS. AFTER 21Z THE HIGHER RATES
SHOULD BE MAINLY CONFINED TO THE NORTHERN CA CASCADES...WHERE
UPSLOPE FLOW WILL CONTINUE TO BE A BIT STRONGER.  ADDITIONAL
RAINFALL AMOUNTS OVER THE NEXT 12 HOURS OF 1-2" SEEM PROBABLE
ACROSS THE PORTIONS OF COASTAL CA HIGHLIGHTED...WITH PRECIPITATION
AMOUNTS OF 3-4" POSSIBLE ACROSS THE NORTHERN CA CASCADES.

CHENARD

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

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

LAT...LON   41772174 41592120 41052084 39992062 38932153 
            38252207 37752228 37342256 37152300 37522348 
            37962348 38372366 39182337 39972329 40422327 
            41322273 41732209