483  
FXUS66 KPQR 142221  
AFDPQR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PORTLAND OR  
220 PM PST THU DEC 14 2017  
   
SYNOPSIS
 
INCREASING CLOUDS LATER TODAY AND TONIGHT, ESPECIALLY  
ACROSS THE NORTHWESTERN HALF OF THE FORECAST AREA, AS A FRONT WILL  
APPROACH THE REGION. THE FRONT WILL PUSH ONSHORE EARLY FRIDAY,  
BRINGING RAIN AND A RETURN TO ONSHORE FLOW. INCREASING SOUTHWESTERLY  
FLOW ALOFT NEXT WEEK WILL BRING A SERIES OF FRONTS INTO THE REGION,  
WITH LOWLAND RAIN AND MOUNTAIN SNOW AT TIMES DURING AT LEAST THE  
FIRST HALF OF THE WEEK.  
 

 
   
SHORT TERM
 
TODAY THROUGH SUNDAY..A DRY AIR MASS REMAINS IN PLACE  
OVER THE REGION TODAY WITH CONTINUED OFFSHORE FLOW. STRONGEST WINDS  
WILL CONTINUE TO BE IN AND AROUND THE COLUMBIA RIVER GORGE, WHERE  
EAST WINDS WILL GUST TO 50 TO 65 MPH. THE AIR STAGNATION ADVISORY FOR  
AREAS IN WASHINGTON ENDED AT 2 PM, BUT IT WILL EXTEND FOR THE CENTRAL  
AND SOUTHERN WILLAMETTE VALLEY THROUGH 10 AM FRIDAY, IN COLLABORATION  
WITH STATE AND LOCAL AIR QUALITY PARTNERS. STAGNANT CONDITIONS WILL  
FINALLY COME TO AN END FRIDAY MORNING AS THE FRONT ARRIVES, PROVIDING  
FOR INCREASED MIXING AND SOME RAIN.  
 
EXPECT INCREASED CLOUDS BY DAYBREAK, WITH LIGHT RAIN MOVING INTO THE  
COAST LATER IN THE MORNING AND INTO THE INTERIOR BY EARLY AFTERNOON.  
TRENDED QPF AMOUNTS SLIGHTLY HIGHER, IN LINE WITH TRENDS IN MODEL  
GUIDANCE, BUT GENERALLY AROUND ONE TO TWO TENTHS OF AN INCH OF RAIN  
FOR THE LOWLAND LOCATIONS AND LARGER AMOUNTS IN THE WILLAPA HILLS AND  
S WA/N OR CASCADES. WILL CONTINUE TO EVALUATE THE THREAT FOR ANY  
FREEZING RAIN (MOSTLY IN HOOD RIVER AND THE HOOD RIVER VALLEY), BUT  
STILL BELIEVE THE MOISTURE WILL ARRIVE AFTER WEST WINDS DEVELOP,  
WHICH SHOULD ENABLE TEMPERATURES TO RISE INTO THE MID 30S BEFORE  
PRECIPITATION STARTS. SOME POCKETS OF COOLER AIR MAY LINGER IN  
SHELTERED SPOTS, SO THOSE TRAVELING EARLY IN THE DAY SHOULD BE AWARE  
THAT A FEW SLICK SPOTS CANNOT BE RULED OUT ENTIRELY.  
 
RAIN WILL TRANSITION TO SHOWERS LATER FRIDAY EVENING, WITH  
DIMINISHING SHOWER COVERAGE OVERNIGHT. SNOW LEVELS WILL FALL BEHIND  
THE FRONT WITH ACCUMULATING SNOW DOWN TO AROUND 2,500 FEET ON  
SATURDAY. HOWEVER, SNOW AMOUNTS SHOULD BE RATHER MODEST WITH LESS  
THAN AN INCH IN THE UPPER FOOTHILLS AND LOWER CASCADES, AND 1-3  
INCHES AT PASS ELEVATION. SNOW LEVELS WILL THEN RISE ABOVE THE  
CASCADE PASSES LATE SATURDAY NIGHT AS A WARM FRONT MOVES THROUGH THE  
REGION. THIS WILL BRING ANOTHER ROUND OF RAIN ON SUNDAY AND HAVE  
MAINTAINED CHANCE POPS ACROSS THIS AREA WITH HIGHEST CHANCES OVER  
SOUTHWESTERN WASHINGTON. HOWEVER, WOULD NOT BE SURPRISED IF AREAS  
SOUTH OF A NEWPORT TO SALEM LINE REMAIN DRY OVER THE WEEKEND.  
CULLEN  
   
LONG TERM...SUNDAY NIGHT THROUGH THURSDAY
 
MODELS ARE IN  
DECENT AGREEMENT THE AREA WILL BE UNDER ZONAL FLOW WITH THE JET  
STREAM REMAINING ACROSS SOUTHERN BRITISH COLUMBIA AND FAR NORTHERN  
WASHINGTON SUNDAY NIGHT AND MONDAY. THIS WILL LEAVE OUR MORE  
NORTHERN ZONES OPEN TO A PERIOD OR TWO OF LIGHT RAIN AS A WEAK FRONT  
DRAGS SOUTHWARD TOWARDS THE REGION, BUT RAIN CHANCES APPEAR  
CONSIDERABLY LESS TOWARDS LANE COUNTY.  
 
MODELS SEEM TO ALSO BE COMING INTO AGREEMENT A SHORTWAVE TROUGH AND  
ATTENDANT FRONT WILL DROP SOUTHEASTWARD OUT OF THE GULF OF ALASKA  
AND USHER IN A GOOD SHOT OF VALLEY RAIN AND MOUNTAIN SNOW TUESDAY  
AND TUESDAY NIGHT. AS UPPER LEVEL RIDGING BUILDS NORTHWARD INTO  
BRITISH COLUMBIA BEHIND THIS FEATURE LATE WEDNESDAY AND THURSDAY,  
OUR FLOW SHOULD BECOME INCREASINGLY NORTHEASTERLY. THIS WILL IN TURN  
LIKELY LOWER SNOW LEVELS TO NEAR THE VALLEY BOTTOM, BUT  
PRECIPITATION WILL ALMOST CERTAINLY HAVE ENDED BY THAT POINT. IF  
PRECIPITATION WERE TO LINGER ACROSS THE AREA WEDNESDAY NIGHT AND  
THURSDAY, OUR FLOW WILL LIKELY NOT BE QUITE AS NORTHEASTERLY, AND AS  
A RESULT, SNOW LEVELS WILL LIKELY BE HIGHER. /NEUMAN  
 

 
   
AVIATION
 
OFFSHORE FLOW PATTERN IN PLACE WITH STRONG HIGH  
PRESSURE EAST OF THE CASCADES AND WEAK THERMAL TROUGH ALONG THE  
OREGON COAST. EASTERLY WINDS FROM THE GORGE WILL CONTINUE TO  
WEAKEN THROUGH THE EVENING THURS, AND INTO FRI MORNING. LIGHT  
WINDS WILL DOMINATE AS THE WEEKEND APPROACHES.  
 
PDX AND APPROACHES...VFR CONDITIONS THROUGH 00Z SATURDAY.  
EASTERLY WINDS CONTINUE TO WEAKEN THOUGH FRI MORNING.  
 

 
   
MARINE
 
WINDS IN GENERAL SHOULD START TO TURN, AND COME FROM  
THE NW, AS WEAK COLD FRONT WILL BEGIN TO BREAK DOWN THE HIGH  
PRESSURE SYSTEM THIS EVENING. THE FRONT WILL MOVE ACROSS THE  
COASTAL WATERS EARLY FRI MORNING, BEHIND THIS FRONT WINDS WILL  
INCREASE TO SMALL CRAFT ADVISORY LEVELS FOR THE OUTER NORTHERN  
OREGON WATERS FROM 15Z FRI UNTIL 08Z SAT. SWELL ENERGY FROM THE  
WNW AND SW WILL WILL COMBINE WITH AN INCREASING WIND WAVE  
COMPONENT TO PUSH SEAS UP TO 7-9 FT THU NIGHT/FRI. AFTER A BREAK  
IN THE SWELL SATURDAY AND EARLY SUNDAY, SWELL ENERGY FROM THE  
GULF OF ALASKA WILL PUSH SEAS BACK UP TOWARD 10 FEET OR SLIGHTLY  
HIGHER EARLY NEXT WEEK. IF THE STRONGER SOLUTIONS HOLD FOR THIS  
SYSTEM, GALE STRENGTH WINDS ARE POSSIBLE FOR TUESDAY AND TUESDAY  
NIGHT. HOWEVER, MODELS ARE UNCERTAIN AS TO THE STRENGTH OF THE  
SYSTEM.  
 

 
   
PQR WATCHES/WARNINGS/ADVISORIES
 
 
OR...AIR STAGNATION ADVISORY UNTIL 10 AM PST FRIDAY FOR CENTRAL  
WILLAMETTE VALLEY-SOUTH WILLAMETTE VALLEY.  
 
WA...NONE.  
 
PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 7 AM FRIDAY TO MIDNIGHT PST  
FRIDAY NIGHT FOR WATERS FROM CAPE SHOALWATER WA TO  
FLORENCE OR FROM 10 TO 60 NM.  
 

 
 

 
 
INTERACT WITH US VIA SOCIAL MEDIA:  
WWW.FACEBOOK.COM/NWSPORTLAND  
WWW.TWITTER.COM/NWSPORTLAND  
 
THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON  
FROM THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THIS AREA IS  
COMMONLY REFERRED TO AS THE CWA, OR FORECAST AREA.  
 
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