MESOSCALE PRECIPITATION DISCUSSION 0044
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
443 AM EST TUE FEB 07 2017
 
AREAS AFFECTED...PORTIONS OF CNTRL TO N-CNTRL CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 070942Z - 072100Z
 
SUMMARY...RAINFALL RATES ARE EXPECTED TO GRADUALLY INCREASE EARLY
THIS MORNING AS AN IMPRESSIVE SURGE OF LOW-LEVEL MOISTURE MOVES
ONSHORE. THE HEAVIEST RATES SHOULD FOCUS ALONG THE COASTAL RANGES
AS WELL AS ACROSS PORTIONS OF THE SIERRA NEVADA.

DISCUSSION...LATEST GOES WEST WATER VAPOR IMAGERY SHOWED A
WELL-DEFINED SHORTWAVE TROUGH NEAR 40N 134W MOVING EAST. THE AMSU
89 GHZ CHANNEL REVEALED A T-BONE LIKE FRONTAL STRUCTURE WITH AN
ELONGATED OCCLUSION EXTENDING WESTWARD FROM A DEVELOPING SURFACE
LOW APPROXIMATELY 300 MILES WEST OF THE NORTHERN CA COAST. BLENDED
TPW PRODUCT INDICATES PWAT VALUES IN THE 1.0 TO 1.5 INCH RANGE
OFFSHORE, WITH A CONNECTION EVIDENT TO THE TROPICAL CENTRAL
PACIFIC. THESE PWAT VALUES LINE UP WELL WITH THE LATEST SHORT-TERM
RAP FORECAST. THE LATEST AMSU MICROWAVE RAIN RATE PRODUCT IS
INDICATING RATES OF 0.10 TO 0.25 IN/HR OFFSHORE.

GIVEN THE IMPRESSIVE 50-70 KT LOW-LEVEL FLOW ASSOCIATED WITH THIS
ATMOSPHERIC RIVER, THESE MICROWAVE ESTIMATED RAINFALL RATES
OFFSHORE SHOULD YIELD RATES NEAR 0.50 IN/HR ON LAND GIVEN THE
NEARLY PERPENDICULAR NATURE OF THE FLOW RELATIVE TO THE COAST.
THESE HEAVY RAINFALL RATES WILL BE POSSIBLE ACROSS THE CALIFORNIA
COASTAL RANGES AS WELL AS ON THE WESTERN SLOPES OF THE SIERRA
NEVADA, WHERE SNOW LEVELS WILL BE RAPIDLY INCREASING DUE TO THE
STRONG ONSHORE FLOW.

PRECIPITATION WILL BEGIN TO DECREASE ACROSS THE NORTHERN PORTIONS
OF THE OUTLINED AREA BY MIDDAY AS THE SURFACE LOW MOVES QUICKLY
INLAND OVER THE PACIFIC NORTHWEST AND THE COLD FRONT PUSHES
ONSHORE IN NORTHERN CA. HEAVY RAIN IS EXPECTED TO PERSIST ACROSS
SOUTHERN PORTIONS OF THE OUTLINED AREA THROUGH 21Z. TOTAL
ADDITIONAL RAINFALL TOTALS THROUGH 21Z OF 1 TO 4 INCHES ARE
POSSIBLE...WHICH COULD COMPOUND FLOODING CONCERNS.

RYAN

ATTN...WFO...EKA...HNX...LOX...MTR...REV...STO...

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

LAT...LON   40902393 40902373 40672344 40362302 40112279 
            39702267 39352254 39142240 38792205 38662174 
            38832147 39252138 39562145 40072174 40532184 
            40882172 40762145 40412114 39952074 39452035 
            39042016 38661999 38191989 37881975 37501958 
            37211960 37171989 37462018 37632043 37962070 
            38132114 38042147 37772151 37422136 36842136 
            36302132 35852111 35722134 35972169 36512209 
            37052252 37752283 38502350 39372389 39952402 
            40392424 40722418