MESOSCALE PRECIPITATION DISCUSSION 0663
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1018 AM EST THU DEC 03 2015
 
AREAS AFFECTED...WESTERN WA...WESTERN OR...NORTHWEST CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 031515Z - 032030Z
 
SUMMARY...HEAVIER RAINS WILL BE ARRIVING THROUGH LATE MORNING OVER
SOUTHWEST OR AND NORTHWEST CA...WITH PERSISTENT MODERATE TO HEAVY
RAINS FARTHER NORTH OVER THE OLYMPIC PENINSULA.

DISCUSSION...THE LATEST IR SAT IMAGERY SHOWS A STRONG UPPER TROUGH
OFFSHORE THE WEST COAST ALONG WITH A DEEPLY OCCLUDED CYCLONE. A
COMBINATION OF IR AND WV IMAGERY SHOWS A STRONG SHORTWAVE THOUGH
ROUNDING THE BASE OF THE UPPER TROUGH OFFSHORE NORTHERN CA WHICH
IS HELPING TO ENHANCE LOW PRESSURE DEVELOPING WEST OF THE OR
COASTLINE. THIS IS ALSO INCREASING THE SHOWER ACTIVITY ALONG AND
JUST AHEAD OF THE FRONTAL ZONE WHICH IS CONFIRMED BY CONVENTIONAL
IR SATELLITE IMAGES AND A 1330Z AMSU PASS.

THE 1330Z AMSU PASS SHOWS RAIN RATES OF 0.40 TO 0.60 INCHES/HR IN
TWO SEPARATE AREAS...WITH ONE FOCUS JUST OFF THE SOUTHWEST
OR/NORTHWEST CA COASTLINE...AND ALSO FARTHER NORTH ALONG THE FRONT
OFF THE WA COAST. OVER THE NEXT SEVERAL HOURS...THE HEAVIEST RAINS
SHOULD BEGIN TO FOCUS ACROSS SOUTHWEST OR AND NORTHWEST CA WHERE
THE APPROACHING UPSTREAM SHORTWAVE WILL FAVOR STRONG LARGE SCALE
ASCENT AND COUPLE WITH A S/SW 850 MB JET OF 50 TO 70 KTS AND A
NOSE OF 1 TO 1.2 INCH PWATS FOR ENHANCED RAINFALL RATES. RAINFALL
RATES OVER THE IMMEDIATE COASTAL RANGES MAY APPROACH OR EXCEED
0.75 INCHES/HR WITH THE AID OF STRONG OROGRAPHICS...AND THIS WILL
MAINLY BE FOR THE SOUTHWEST FACING SLOPES OF THE TERRAIN. EXPECT
RAINFALL AMOUNTS OF UP TO 2 TO 2.5 INCHES FOR THE COASTAL RANGES
HERE THROUGH ABOUT 20Z. 

FARTHER NORTH...STRONG AND BROAD WARM ADVECTION WILL CONTINUE TO
FOCUS MODERATE TO LOCALLY HEAVY RAINS OVER THE OLYMPIC PENINSULA
AND SOME ADJACENT COASTAL RANGES OF WESTERN WA...BUT THE RAINFALL
RATES HERE SHOULD TEND TO BE A BIT LOWER GIVEN SOMEWHAT WEAKER
MOISTURE TRANSPORT. MORNING RUNS OF THE HRRR SUGGEST ADDITIONAL
RAINFALL AMOUNTS OF 1.5 TO 2 INCHES OVER THE OLYMPIC PENINSULA
THROUGH ABOUT 20Z.

ORRISON

ATTN...WFO...EKA...MFR...PQR...SEW...STO...

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

LAT...LON   49132393 48472288 47082250 44452269 41862300 
            39002285 38732370 40592431 41822451 44182420 
            45692416 47192443 48472466