935  
AWUS01 KWNH 212048  
FFGMPD  
ORZ000-WAZ000-220445-  
 
MESOSCALE PRECIPITATION DISCUSSION 0941  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
348 PM EST TUE NOV 21 2017  
 
AREAS AFFECTED...FAR NORTHWESTERN OR INTO WESTERN WA  
 
CONCERNING...HEAVY RAINFALL  
 
VALID 212047Z - 220445Z  
 
SUMMARY...RAINFALL RATES CURRENTLY PEAKING IN INTENSITY ACROSS  
WESTERN WA WILL BEGIN TO WANE PAST 00Z. AN ADDITIONAL 2-4 INCHES  
OF RAIN IS EXPECTED BY 04Z ACROSS THE OLYMPICS...SELECTED COASTAL  
RANGES INTO THE WASHINGTON CASCADES.  
 
DISCUSSION...BLENDED TPW IMAGERY THROUGH 18Z SHOWED A LARGE AREA  
OF ANOMALOUS PRECIPITABLE WATER VALUES RANGING BETWEEN 200-300  
PERCENT OF NORMAL...EXTENDING FROM THE PACIFIC NORTHWEST COAST TO  
AND BEYOND 130W AND EXTENDING SWW TO ABOUT 25N. PRECIPITABLE WATER  
VALUES WITHIN THE CORE OF THE ANOMALOUS MOISTURE AXIS...WHICH  
SHOWED A DIRECT CONNECTION TO THE ITCZ...WERE WIDESPREAD OF 1.5+  
INCHES PEAKING NEAR 2 INCHES AS FAR NORTH AS 34N 132W. GPS DATA  
SHOWED MAXIMUM PRECIPITABLE WATER VALUES OF 1.3 TO 1.4 INCHES  
ALONG MOST OF THE WA COASTLINE. 20Z VWP DATA FROM KLGX SHOWED 850  
MB WINDS OF 75 KT FROM THE SSW...ARRIVING SLIGHTLY QUICKER THAN  
EARLIER FORECASTS. THESE WINDS REPRESENT A 20 KT INCREASE SINCE  
16Z WITH OBSERVED RAINFALL RATES OF NEAR 0.5 TO 0.6 IN/HR OBSERVED  
IN THE OLYMPICS.  
 
AS A SHORTWAVE NEAR 49N 132W CONTINUES TO TRACK NORTHEASTWARD INTO  
BRITISH COLUMBIA OVER THE NEXT 3-6 HOURS...850 MB WIND SPEEDS  
ALONG THE CENTRAL WASHINGTON COASTLINE WILL BEGIN TO  
WEAKEN...REACHING 40 KT BY 03Z PER THE LATEST CONSENSUS OF HI-RES  
MODEL FORECASTS...
AND AS THE MOISTURE AXIS SLIDES SOUTH. MAXIMUM  
WIND SPEEDS WITHIN THE MOISTURE AXIS ARE EXPECTED TO RANGE BETWEEN  
50-60 KT BY 03Z ALONG THE CENTRAL TO SOUTHERN OR COAST. WEAKENING  
TRENDS IN A 150 KT UPPER LEVEL SPEED MAX LOCATED EAST OF A LARGE  
SCALE CLOSED LOW LOCATED NEAR 147W ARE ALSO EXPECTED TO CONTINUE  
THROUGH 06Z.  
 
THE RESULT WILL BE CONTINUING RAINFALL RATES PEAKING BETWEEN 0.5  
AND 0.6 IN/HR FROM THE OLYMPICS INTO THE WASHINGTON CASCADES AND  
THE COASTAL RANGES STRADDLING THE OR/WA BORDER OVER THE NEXT  
SEVERAL HOURS. LOCALLY HIGHER RATES MAY BE OBSERVED...BUT  
WEAKENING WILL OCCUR FROM NORTH TO SOUTH AS THE MOISTURE AXIS  
EDGES DOWN THE COAST TONIGHT. AN ADDITIONAL 2-3 INCHES...LOCALLY  
NEAR 4 INCHES OF RAIN IS EXPECTED IN THESE LOCATIONS THROUGH 04Z.  
 
OTTO  
   
..PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT
 
 
ATTN...WFO...OTX...PDT...PQR...SEW...  
 
ATTN...RFC...NWRFC...  
 
LAT...LON 49102062 49032010 48572006 47932030 47512080  
46942120 46532134 45992169 45742199 45912293  
45472346 45632396 46442412 46992412 47542438  
47902427 48122376 47872299 48002252 48122225  
48642223 48942196 49072145  
 
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