MESOSCALE PRECIPITATION DISCUSSION 0008
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
850 AM EST FRI FEB 06 2015
 
AREAS AFFECTED...NRN CA...SRN OR 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 061349Z - 061849Z
 
SUMMARY...HIGH CONFIDENCE IN A PERIOD OF HEAVY RAINFALL BETWEEN 15
AND 21 UTC. WIDESPREAD RATES OF 1.5" IN 3 HOURS ARE EXPECTED.
HEAVIER RATES ARE LIKELY IN SOUTH AND SOUTHWEST FACING TERRAIN.
FLASH FLOODING IS POSSIBLE.

DISCUSSION...RAIN WAS ALREADY WIDESPREAD IN FAR NORTHERN CA AND
SOUTHERN OR. INTENSIFICATION IS FORECAST AS UPPER LEVEL HEIGHT
FALLS LEAN INTO THE REGION...ALLOWING A 60 KNOT LOW LEVEL JET TO
ADVANCE INLAND DURING THE DAY. CAUGHT UP IN THIS CORRIDOR OF
ENHANCED ONSHORE FLOW IS A RIVER OF RICH MOISTURE CHARACTERIZED BY
PRECIPITABLE WATER AROUND 1.25 INCHES AT THE COAST. PRONOUNCED
SHORTWAVES...ONE HEADING INTO EASTERN OR THIS AFTERNOON AND
ANOTHER APPROACHING NORTHERN CA...WILL COUPLE AT THE UPPER JET
LEVEL TO PRODUCE VERY DEEP ASCENT PER RAP SOUNDINGS. AT THE SAME
TIME...THE STRONG SOUTH TO SOUTHWESTERLY LOW LEVEL FLOW WILL
ENHANCE RAIN RATES WHERE IT ENCOUNTERS STEEP TERRAIN RISES...SUCH
AS IN THE SHASTA RANGE AND THE SOUTHERN END OF THE MENDOCINO
NATIONAL FOREST.

MODELS SHOW STRONG AGREEMENT...SUCH THAT EVEN A MODEL AVERAGE
PRODUCT SUCH AS THE SSEO MEAN PREDICTS PRECIPITATION LOCALLY
TOPPING 3 INCHES IN 6 HOURS. THE SREF INDICATES MAXIMUM RATES
GREATER THAN 1.5 INCHES IN 3 HOURS...WHICH WOULD GET CLOSE TO
FLASH FLOOD GUIDANCE VALUES. BRIEF CONVECTIVE ENHANCEMENT...AND
RAIN EXCEEDING THE ROUGHLY 1 INCH IN 1 HOUR FFG VALUES...IS ALSO
POSSIBLE. CONVECTION IS MORE LIKELY SOUTH OF A EUREKA TO REDDING
LINE AS SEEN IN SIMULATED REFLECTIVITY FROM RECENT HRRR RUNS. THE
EVENT WILL GRADUALLY EXPAND TOWARD NORTHERN SAN FRANCISCO BAY AND
ACROSS THE SACRAMENTO VALLEY TOWARD THE NORTHERN SIERRAS.  

BURKE

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

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

LAT...LON   43172451 43082428 42952367 42732333 42342326 
            42182294 42312275 42172251 41802248 41632235 
            41722189 41642171 40962152 40382103 39802070 
            39532082 39282122 39022167 38612183 38132212 
            38032274 38082315 38522382 38962417 39122424 
            39772444 41832465 43032466