395  
FXUS66 KPQR 252121  
AFDPQR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PORTLAND OR  
221 PM PDT FRI MAY 25 2018  
   
SYNOPSIS
 
A LOW OVER NORTHERN CALIFORNIA WILL CONTINUE TO SPREAD  
SHOWERS ACROSS THE OREGON CASCADES THIS AFTERNOON AND EVENING,  
POSSIBLY AFFECTING THE EASTERN EDGE OF THE WILLAMETTE VALLEY. ONSHORE  
FLOW WILL CONTINUE THROUGH SATURDAY AS A WEAK SYSTEM APPROACHES AND  
THEN PASSES BY TO THE NORTH SATURDAY, WITH A DISSIPATING FRONT MOVING  
THROUGH, POSSIBLY PRODUCING SOME DRIZZLE OR LIGHT SHOWERS LATE  
TONIGHT AND SATURDAY. A RETURN TO DRY WEATHER AND SLIGHTLY ABOVE  
NORMAL DAYTIME TEMPERATURES CAN BE EXPECTED SUNDAY INTO EARLY NEXT  
WEEK WITH A MORE SEASONAL NIGHT AND MORNING CLOUDS REGIME. THE NEXT  
WEAK UPPER TROUGH IS EXPECTED AROUND THE MIDDLE OF NEXT WEEK WITH  
INCREASED ONSHORE FLOW, COOLER TEMPERATURES, AND SPOTTY  
PRECIPITATION.  

 
   
SHORT TERM...TONIGHT THROUGH MONDAY
 
SOUTHWEST WASHINGTON AND  
NORTHWEST OREGON REMAINS IN BETWEEN TWO SYSTEMS. THE FIRST SYSTEM IS  
AN UPPER LOW NOW OVER NORTHERN CALIFORNIA THAT HAS BEEN THE MAIN  
DRIVER OF OUR RECENT SHOWERS AND THUNDERSTORMS OVER THE CASCADES.  
THIS SYSTEM IS CURRENTLY SPREADING SHOWERS UNDER A DEFORMATION ZONE  
NORTH OF THE LOW. NATIONAL WEATHER SERVICE DOPPLER RADAR SHOWS THAT  
THE MAIN PRECIPITATION IS IN SOUTHWEST OREGON SIMILAR TO THE MODELS,  
BUT RADAR AND WEB CAMS SHOW THE BAND OF SHOWERS EXTENDING NORTH ALONG  
THE CASCADES TO NEAR OR JUST NORTH OF MOUNT JEFFERSON. IT IS POSSIBLE  
A FEW OF THE SHOWERS MAY DRIFT OFF INTO THE EASTERN WILLAMETTE VALLEY  
BEFORE DISSIPATING. THIS IS IN LINE WITH RECENT MODEL FORECASTS. THE  
MODELS STILL SHOW IT WILL BE STABLE IN OUR FORECAST AREA WITH ANY  
THUNDER IN CENTRAL OREGON AND EASTWARD, AND WITH THE LAYERED CLOUDS  
ON SATELLITE IMAGERY, THIS STILL SEEMS REASONABLE AS WELL.  
 
OTHERWISE WEST OF THE CASCADES SHOULD BE MOSTLY DRY TONIGHT. CLOUDS  
HAVE THINNED IN THE FAR WESTERN SECTIONS OF THE FORECAST AREA BUT  
WILL STAY RATHER CLOUDY CLOSER TO THE CASCADES.  
 
THE LOW TO OUR SOUTH WILL MOVE SLOWLY EASTWARD TONIGHT AND SATURDAY  
AS A WEAK SYSTEM MOVES THROUGH TO OUR NORTH TONIGHT AND SATURDAY. THE  
MODELS SHOW A DISSIPATING FRONTAL BOUNDARY WITH THIS NORTHERN SYSTEM  
MOVING INTO AND THROUGH OUR FORECAST AREA, AND THIS IS LIKELY THE  
REASON WHY THE MODELS ARE PRODUCING SOME LIGHT DRIZZLE OR SHOWERS  
MAINLY NEAR THE COAST AND INLAND TO AROUND KELSO LATE TONIGHT AND  
THEN OVER MUCH OF THE INLAND AREAS SATURDAY. QPF WILL BE LIGHT AND  
POPS WILL BE KEPT LOW, THOUGH WE HAVE SOME LOW CHANCE POPS IN SOME  
AREAS. THIS WILL ALSO KEEP CLOUDS AROUND THROUGH THE DAY SATURDAY,  
ESPECIALLY IN THE INLAND AREAS.  
 
A POSITIVE TILT UPPER RIDGE BUILDS IN SATURDAY NIGHT AND SUNDAY,  
TRANSITIONING THE WEATHER TO A MORE TYPICAL OR SEASONAL NIGHT AND  
MORNING CLOUDS AFTERNOON SUNSHINE REGIME. TEMPERATURES ON SUNDAY WILL  
BE RISING BACK INTO THE MID 70S. NOT MUCH CHANGE ON MONDAY AS  
COMPARED TO SUNDAY, THOUGH THE MODELS DO START TO LOWER THE 500 MB  
HEIGHTS AND INCREASE THE ONSHORE FLOW A BIT LATER IN THE DAY AHEAD OF  
THE NEXT APPROACHING OFFSHORE UPPER TROUGH. SUSPECT THE MAIN COOLING  
WILL BE MONDAY NIGHT AND TUESDAY. TOLLESON  
   
LONG TERM...MONDAY NIGHT THROUGH FRIDAY
 
THE MODELS SHOW AN  
APPROACHING AND DIGGING UPPER TROUGH OFF THE COAST MONDAY NIGHT AND  
TUESDAY, WITH A SHORT WAVE THAT SWINGS THROUGH TUESDAY NIGHT AND  
EARLY WEDNESDAY. THE UPPER TROUGH REMAINS IN THE REGION THURSDAY AND  
FRIDAY THROUGH THE GFS MODEL IS STRONGER THAN ON THE ECMWF. THE MAIN  
EFFECT IS THAT IT WILL BE COOLER, CLOUDIER, WITH POSSIBLY SOME SPOTTY  
LIGHT PRECIPITATION ESPECIALLY NORTH, THOUGH DETAILS ARE UNCERTAIN  
LATER NEXT WEEK. TOLLESON  

 
   
AVIATION
 
MOSTLY VFR CONDITIONS ACROSS THE AREA THIS AFTERNOON.  
SCATTERING CLOUDS ALONG AND WEST OF A K6S2-KKLS LINE HAVE IMPROVED  
CONDITIONS CONSIDERABLY. HOWEVER, MOISTURE AND ASSOCIATED CLOUD FIELD  
CONTINUES TO ROTATE INTO THE EASTERN AND CENTRAL PORTIONS OF THE  
FORECAST AREA WITH LOW VFR CIGS PERSISTING. MEANWHILE, GUSTY WINDS  
ACROSS THE NORTHERN HALF OF THE FORECAST AREA WILL DEVELOP AND  
PERSIST THROUGH THE LATE AFTERNOON/EARLY EVENING. STRONGER ONSHORE  
FLOW TONIGHT SHOULD AGAIN BRING A RETURN TO WIDESPREAD MVFR CIGS  
FIRST TO THE COAST AND LATER ACROSS THE INTERIOR.  
 
KPDX AND APPROACHES...VFR CIGS THIS AFTERNOON WITH SOME SCATTERING  
POSSIBLE LATE THIS AFTERNOON. GUSTY WEST WINDS 23Z-04Z WITH GUSTS TO  
15-20 KT. EXPECT A RETURN OF MVFR CIGS LATE OVERNIGHT THROUGH EARLY  
SATURDAY AS MOIST ONSHORE FLOW CONTINUES. CULLEN  

 
   
MARINE
 
HIGH PRESSURE REMAINS OVER THE NORTHEAST PACIFIC WITH LOWER  
PRESSURE OVER NORTHERN CALIFORNIA. THIS WILL MAINTAIN NORTH TO  
NORTHWEST WINDS ACROSS THE COASTAL WATERS THROUGH THE WEEKEND AND  
INTO THE START OF NEXT WEEK. GUSTS SHOULD REMAIN GENERALLY BETWEEN 10  
AND 20 KT WITH SEAS HOLDING BETWEEN 5 AND 7 FEET. BUOY 46050 RECORDED  
GUSTS MEETING ADVISORY CRITERIA FOR SEVERAL HOURS, BUT THESE HAVE  
LARGELY COME TO AN END. THEREFORE, HAVE CANCELLED THE ADVISORY A FEW  
HOURS EARLY, THOUGH A FEW OCCASIONAL GUSTS AROUND 20-25 KT CANNOT BE  
ENTIRELY RULED OUT. NORTHERLY WINDS WILL LIKELY INCREASE DURING THE  
EARLY TO MIDDLE PART OF NEXT WEEK (PERHAPS AS EARLY AS LATE SUNDAY  
NIGHT OR MONDAY), WHICH WILL LIKELY CREATE STEEP AND HAZARDOUS SEAS.  
CULLEN  

 
   
PQR WATCHES/WARNINGS/ADVISORIES
 
 
OR...NONE.  
WA...NONE.  
PZ...NONE.  
 

 
 

 
 
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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