MESOSCALE PRECIPITATION DISCUSSION 0667
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
843 AM EST MON DEC 07 2015
 
AREAS AFFECTED...WA...OR 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 071343Z - 072113Z
 
SUMMARY...ADDITIONAL 2-5 INCH RAINFALL IS FORECAST TODAY IN PARTS
OF WESTERN OREGON AND SOUTHWEST WASHINGTON. THIS WILL OVERLAP WITH
AREAS THAT RECEIVED 2 TO 4 INCHES OVERNIGHT.

DISCUSSION...A STRONG ATMOSPHERIC RIVER EVENT WAS ONGOING AS OF
MONDAY MORNING... AND WILL CONTINUE IN EARNEST THROUGH LATE
AFTERNOON OVER PARTS OF WA/OR. A LOW AMPLITUDE LEAD WAVE WAS
EVIDENT IN MODEL ANALYSES AND SATELLITE IMAGERY OVER EASTERN
WA/OR...HAVING BROUGHT 1.25 INCH PW VALUES TO THE IMMEDIATE OREGON
COAST. ALTHOUGH 12Z SOUNDINGS AT SLE AND MFR SAMPLED SLIGHTLY
LOWER VALUES BETWEEN 1.0 AND 1.10 INCHES...BLENDED TPW PRODUCTS
AND RAP ANALYSES INDICATED A RIVER CHARACTERIZED BY 1.25 INCH PW
EXTENDING FROM THE COAST WELL BACK INTO THE CENTRAL PACIFIC...WITH
1.40 INCH PW EMBEDDED JUST OFFSHORE. THESE VALUES WOULD BE NEAR
THE CLIMATOLOGICAL MAXIMUM FOR EARLY DECEMBER SHOULD THEY BE
REALIZED AT SLE...MFR LATER TODAY AS FORECAST BY THE RAP.

EVEN IN THE WAKE OF THE LEAD WAVE... MODERATE ONSHORE FLOW AND
EXTENSIVE COVERAGE OF RAINFALL CONTINUED AS OF 13Z. DEEP LAYER
LIFT WILL INCREASE FURTHER BY 17-18Z AND 700 MB FLOW IS FORECAST
TO ACCELERATE BACK UP TO 60-PLUS KNOTS FROM ABOUT 250 DEGREES AS A
150 KNOT JET STREAK AND POSITIVE-TILT LARGE SCALE SHORTWAVE
CENTERED NEAR 46 N / 138 W...RAPIDLY ADVANCE TOWARD WESTERN
OREGON. MOISTURE FLUX AT 850 MB BECOMES MAXIMIZED AT 4.5 STANDARD
DEVIATIONS IN A HIGHLY FOCUSED CORRIDOR OVER WESTERN OREGON AROUND
18Z PER 06Z GEFS ANOMALIES.

WPC AND NDFD FORECAST LOCAL AMOUNTS GREATER THAN 4 INCHES THROUGH
00Z IN THE COASTAL RANGES AND CASCADES...STRADDLING THE COLUMBIA
RIVER...BUT EVENTUALLY SLIDING SOUTHWARD TO INCLUDE MORE OF
OREGON...ESPECIALLY AFTER 21Z.

BURKE

ATTN...WFO...MFR...PDT...PQR...SEW...

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

LAT...LON   47192164 47082141 46422117 44492160 43872168 
            43022226 42982272 42902334 42252357 42012388 
            42712477 46072465 47082299