MESOSCALE PRECIPITATION DISCUSSION 0019
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
458 PM EST WED JAN 27 2016
 
AREAS AFFECTED...WASHINGTON OLYMPICS / WASHINGTON COASTAL RANGES 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 272154Z - 280900Z
 
SUMMARY...HOURLY RAIN RATES BETWEEN 0.50 - 0.75 IN/HR ARE EXPECTED
TO REACH THE SSW FACING SLOPES OF THE OLYMPICS BETWEEN 03-06Z
AHEAD OF AN ADVANCING COLD FRONT. THESE RATES COULD CAUSE 12 HOUR
RAINFALL TOTALS OF 3-4 INCHES IN SOME LOCATIONS BY 09Z.

DISCUSSION...WATER VAPOR IMAGERY AT 21Z SHOWED A SHORTWAVE NEAR
42N 138W...LOCATED ON THE SOUTHEAST SIDE OF A LARGE CYCLONIC
CIRCULATION...CENTERED IN THE GULF OF ALASKA. THIS FEATURE APPEARS
TO BE CONNECTED TO A WEAK COLD FRONTAL WAVE...EXPECTED TO MOVE
NORTHEASTWARD OVER THE NEXT 6-12 HOURS...SLOWING THE EVENTUAL
FRONTAL PROGRESSION ACROSS THE PACIFIC NORTHWEST COAST. AHEAD OF
THE COLD FRONT...BLENDED TPW IMAGERY MATCHED WITH RECENT RAP
FORECASTS/ANALYSES INDICATING A PLUME OF 1.00 TO 1.25+ INCHES IN
PLACE...WITH WINDS OF 60-70 KTS WEST OF WASHINGTON/OREGON AT 21Z.
ALOFT...A SPEED MAX OF 110 TO 130 KTS WAS NOTED VIA GOES HD WINDS
NEAR 300 MB NEAR 45N 132W...WITH THE RIGHT ENTRANCE REGION
FORECAST TO APPROACH WRN WASHINGTON BETWEEN 03-09Z ALONG WITH
MODEST DIFFLUENCE. SEVERAL RECENT MICROWAVE PASSES...CONFIRMED BY
SAB...INDICATE HOURLY RATES ARE TOPPING OFF ONLY NEAR 0.20 TO 0.30
IN/HR VIA SSMIS/AMSU JUST AHEAD OF THE COLD FRONT TO THE WEST OF
WASHINGTON/OREGON.

GIVEN LOW LEVEL WINDS ARE LARGELY FROM...AND SHOULD STAY FROM THE
SOUTH...HEAVY RAIN IMPACTS ARE FORECAST TO BE FOCUSED MAINLY INTO
THE SOUTHWEST FACING SLOPES OF THE OLYMPICS AND PERHAPS SOUTH
FACING SLOPES OF THE WASHINGTON COASTAL RANGES. SOME ENHANCEMENT
DUE TO THE UPPER JET MAX AND OROGRAPHIC INFLUENCES SHOULD AUGMENT
CURRENT RATES ABOVE 0.50 IN/HR AFTER ABOUT 03Z. GIVEN THESE RATES
COULD REMAIN OVER THE REGION THROUGH 09Z...12 HR RAINFALL TOTALS
OF 3-4 INCHES WILL BE POSSIBLE BY 09Z. THESE NUMBERS HAVE BEEN
SUBSTANTIATED BY A NUMBER OF RECENT CAM ALLOWING
GUIDANCE...INCLUDING RECENT RUNS OF THE HRRR.
 
OTTO

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

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

LAT...LON   48232471 48162384 48072333 47732299 47152314 
            46462303 46202316 46292354 46322399 46692425 
            47382438