MESOSCALE PRECIPITATION DISCUSSION 0764
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
446 AM EDT SAT NOV 05 2016
 
AREAS AFFECTED...WESTERN WA...WESTERN OR 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 050845Z - 051800Z
 
SUMMARY...HEAVY RAIN WILL CONTINUE ACROSS WESTERN WA INCLUDING THE
OLYMPIC PENINSULA THROUGH MID-MORNING WITH SOME OF THIS RAINFALL
FOCUSING SOUTH DOWN ACROSS THE COASTAL RANGES OF WESTERN OR.

DISCUSSION...AN UPPER TROUGH OFFSHORE THE PACIFIC NORTHWEST
CONTINUES TO ALLOW A COLD FRONT TO GRADUALLY APPROACH THE COASTAL
RANGES OF WESTERN WA AND WESTERN OR. THE LATEST RAP ANALYSIS SHOWS
A 130-150KT 250 MB JET CORE LIFTING NORTHEAST AROUND THE EASTERN
FLANK OF THE UPPER TROUGH WHICH IS HELPING TO FOSTER FAVORABLE
RIGHT-ENTRANCE REGION JET DYNAMICS JUST OFFSHORE IN VICINITY OF
THE COLD FRONT. THESE STRONGER DYNAMICS ARE RESULTING IN AN AXIS
OF COLDER CLOUD TOPS/FORCING AS DENOTED IN GOES-W IR IMAGERY...AND
HEAVIER RAINFALL RATES OF 0.30 TO 0.40 INCHES/HR AS CONFIRMED BY A
PAIR OF AMSU PASSES AT 0452Z AND 0539Z RESPECTIVELY.

THE LATEST BLENDED-TPW IMAGERY SHOWS AN AXIS OF HIGHER PWATS
REACHING AS HIGH AS 1.5 TO 1.6 INCHES JUST AHEAD OF THE FRONT
OFFSHORE WESTERN OR...AND THESE VALUES ARE A SOLID 3 TO 4 STANDARD
DEVIATIONS ABOVE NORMAL WHICH IS HELPING TO CONTRIBUTE TO THE
HEAVIER RAINFALL RATES. SOUTHWEST 850 MB FLOW AHEAD OF THE FRONT
IS CURRENTLY ON THE ORDER OF ABOUT 40 KTS...AND THIS WILL FAVOR
HEAVY OROGRAPHICALLY ENHANCED RAINS ACROSS ESPECIALLY THE OLYMPIC
PENINSULA OF WESTERN WA OVER THE NEXT SEVERAL HOURS. THE
AFOREMENTIONED CORE OF STRONGER UPPER JET FORCING IS EXPECTED TO
CROSS THIS REGION TOO THROUGH THE EARLY MORNING HOURS. THIS SHOULD
PROMOTE ADDITIONAL HEAVY RAIN WILL RATES OF AS MUCH AS 0.50 TO
0.70 INCHES/HR. ADDITIONAL STORM TOTALS OF AS MUCH AS 2 TO 3
INCHES ARE EXPECTED THROUGH MID-MORNING OVER THE OLYMPICS.

THE COLD FRONT WILL BEGIN CROSSING WESTERN WA BY MID-MORNING WHICH
WILL BEGIN TO SHUT OFF THE HEAVIER RAINFALL RATES. THE BOUNDARY
WILL THEN GRADUALLY CROSS THE COASTAL RANGES OF WESTERN OR AS
WELL...BUT THE ONSHORE FLOW IS NOT EXPECTED TO BE AS STRONG HERE
AND THE FLOW WILL BE MORE PARALLEL TO THE COAST WHICH WILL LIMIT
THE DEGREE OF OROGRAPHIC FORCING. THUS THE RAINFALL RATES ARE
EXPECTED TO BE NOTABLY LOWER FARTHER SOUTH DOWN THE COAST...WITH
RATES MORE ON THE ORDER OF 0.25 TO 0.50 INCHES/HR AT MOST.

ORRISON

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

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

LAT...LON   48442412 48422330 47652292 46262292 45332311 
            44082342 42782387 42122419 42262458 42972460 
            44502429 45272423 46672423 48102470