862  
FXUS66 KPQR 062111  
AFDPQR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PORTLAND OR  
209 PM PDT MON APR 6 2020  
   
SYNOPSIS
 
HIGH PRESSURE WILL CONTINUE TO STRENGTHEN OVER THE  
PACIFIC NORTHWEST THROUGH WEDNESDAY. STRONGER ONSHORE LOW-LEVEL FLOW  
TONIGHT AND TUESDAY WILL RESULT IN BREEZY TO WINDY CONDITIONS IN THE  
CENTRAL COLUMBIA RIVER GORGE TUESDAY. LIGHT OFFSHORE FLOW DEVELOPS  
WEDNESDAY AND CONTINUES THROUGH EARLY THURSDAY. WEDNESDAY AND  
THURSDAY WILL BE THE WARMEST DAYS OF THE WEEK. A GRADUAL COOLING  
TREND BEGINS FRIDAY AS AS THE UPPER RIDGE WEAKENS. THERE WILL BE A  
CHANCE FOR SOME SHOWER ACTIVITY SATURDAY THROUGH EARLY SUNDAY.  
 

 
   
SHORT TERM...TONIGHT THROUGH THURSDAY
 
EARLY AFTERNOON WATER VAPOR  
LOOP REVEALED A DEEP CLOSED LOW CENTERED OVER THE CENTRAL CALIFORNIA  
COAST AND A 500 MB RIDGE AXIS ALONG 145W. A SHORT-WAVE COULD BE SEEN  
DROPPING SOUTH THROUGH BRITISH COLUMBIA AND NORTHERN WASHINGTON. MOST  
OF THE FORECAST AREA IS WITHIN A CLASSIC COL PATTERN. THIS IS A  
REGION OF MINIMAL TO NO MID AND UPPER LEVEL FLOW. EASTERLY UPPER  
LEVEL FLOW WAS NOTED OVER SOUTHERN OREGON AND NORTHWEST TO WEST FLOW  
ALOFT WAS OCCURRING OVER WASHINGTON AND EXTREME NORTHERN OREGON.  
VISIBLE IMAGERY SHOWED CONSIDERABLE CLOUD COVER ACROSS THE SOUTHERN  
TWO-THIRDS OF THE FORECAST AREA THIS MORNING. THE CLOUD COVER WAS  
STARTING TO DIMINISH EARLY THIS AFTERNOON. THE CLOUD COVER IS  
ASSOCIATED WITH WRAP-AROUND MOISTURE ROTATING THROUGH SOUTHERN OREGON  
AROUND THE CLOSED CALIFORNIA LOW AND THE AFOREMENTIONED UPPER LEVEL  
SHORT-WAVE. HIGH PRESSURE AND INCREASED SUBSIDENCE SPREADS OVER THE  
FORECAST AREA THROUGH THE AFTERNOON.  
 
THE 12Z NAM SHOWS THE SHORT-WAVE WEAKENING CONTINUING TO WEAKEN THIS  
AFTERNOON AS 500 MB HIGH PRESSURE STARTS TO STRENGTHEN. THE NAM ALSO  
INDICATES STRONGER ONSHORE LOW-LEVEL FLOW TONIGHT AND TUE. EXPECT  
MORE LOW CLOUD COVERAGE LATE TONIGHT AND TUE MORNING. HAVE INCREASED  
CLOUD COVER ACCORDINGLY. MODEL 850 MB TEMPS ARE FORECAST TO BE ABOUT  
2-3C LOWER TUE AFTERNOON ACROSS SW WASHINGTON AND THE NORTH  
WILLAMETTE VALLEY COMPARED TO TODAY. THE NAM SUGGESTS LOW CLOUDS WILL  
PERSIST THE LONGEST IN AN AREA FROM NEAR KUAO TO KPDX AND THEN ALONG  
THE COLUMBIA TO NEAR KKLS. THE NAM SHOWS A 5.0 MB KTTD-KDLS GRADIENT  
TUE AFTERNOON. THUS, EXPECT BREEZY CONDITIONS IN THE CENTRAL GORGE,  
WITH GUSTS AT LEAST 25-30 MPH LIKELY.  
 
THE ONSHORE LOW-LEVEL FLOW DECREASES RATHER QUICKLY TUE NIGHT. IN  
FACT, BY 12Z WED THE KTTD-KDLS GRADIENT IS FORECAST TO BE NEARLY NEUTRAL  
OR SLIGHTLY OFFSHORE. A THERMALLY-INDUCED SURFACE TROUGH DEVELOPS  
ALONG THE SOUTH OREGON COAST TUE NIGHT AND EXPANDS NORTH WED. LIGHT  
OFFSHORE FLOW IS EXPECTED TO OCCUR WED, WITH THE KTTD-KDLS GRADIENT  
PEAKING NEAR -3 MB LATE WED MORNING OR EARLY AFTERNOON. MODEL  
FORECAST 850 MB TEMPS JUMP TO AROUND 9C IN SW WASHINGTON TO 12C OVER  
THE LANE COUNTY CASCADES WED. MANY LOCATIONS ARE LIKELY TO REACH THE  
UPPER 60S, WITH SOME LOWER 70S NOT OUT OF THE QUESTION. THE  
THERMALLY-INDUCED SURFACE TROUGH SHIFTS TO THE INLAND VALLEYS WED  
NIGHT AND THEN TO THE EAST SLOPES OF THE CASCADES THU. THE COAST AND  
COASTAL VALLEYS WILL LIKELY BE SLIGHTLY COOLER THU AS LOW-LEVEL  
ONSHORE FLOW RETURNS. AREAS EAST OF THE OREGON COAST RANGE AND THE SW  
WASHINGTON INTERIOR MAY NO CHANGE OR A DEGREE OR TWO COOLING THU. WEISHAAR  
   
LONG TERM...THURSDAY NIGHT THROUGH MONDAY
 
MODELS AND THEIR  
RESPECTIVE ENSEMBLES ARE IN GOOD AGREEMENT THU NIGHT AND FRI SHOWING  
A FLATTENING OF THE 500 MB RIDGE CENTERED OFFSHORE. EXPECT A MARINE  
PUSH OR INCREASING ONSHORE FLOW THU NIGHT AND FRI FOR DRY, BUT COOLER  
DAYTIME CONDITIONS. THE GFS ENSEMBLES SUGGEST MODERATE TO HIGH  
FORECAST CONFIDENCE. THE ECMWF ENSEMBLES INDICATE A 40-50 DM DROP IN  
500 MB HEIGHTS FROM THU AFTERNOON TO FRI. THE 12Z OPERATIONAL ECMWF  
AND GFS SHOW A SHORT-WAVE SLIDING SOUTH THROUGH EASTERN WASHINGTON  
AND OREGON SAT. THE OPERATIONAL ECMWF APPEARS TO BE MORE AGGRESSIVE  
WITH THIS FEATURE AND PAINTS SOME LIGHT QPF ACROSS MUCH OF THE  
FORECAST AREA SAT. 500-MB CLUSTER ANALYSIS VALID SAT WITH HIGHER  
WEIGHTING FOR THE GFS SHOWS SLIGHTLY HIGHER 500 MB HEIGHTS OVER THE  
FORECAST AREA, COMPARED TO THE HIGHER-WEIGHTED ECMWF CLUSTER. HAVE  
GONE WITH SOME LOW-END POPS FOR SAT. THIS MAY TURN OUT TO BE A  
DEEPENING MARINE LAYER THAT PRODUCES SOME DRIZZLE OR VERY LIGHT RAIN.  
 
BY SUN MODELS AND ENSEMBLES SHOW AMPLIFICATION OF THE EASTERN PACIFIC  
RIDGE. THIS RESULT IN NORTH FLOW ALOFT. LEFT SOME TOKEN POPS SAT  
NIGHT THROUGH SUN MORNING AND THEN WENT DRY FOR SUN AFTERNOON. THE  
TOTAL MEAN 500 MB CLUSTER ANALYSIS VALID SUN INDICATES RIDGING CLOSE  
ENOUGH TO THE COASTLINE AND MEAN TROUGHING WELL TO THE EAST FOR  
MODERATE CONFIDENCE IN A DRY FORECAST. WEISHAAR  

 
   
AVIATION
 
HIGH PRESSURE BUILDING OVER THE PACIFIC IS CREATING  
FAIRLY CALM CONDITIONS THROUGH THE FORECAST AREA. SATELLITE  
IMAGERY ALONG WITH GROUND OBSERVATIONS SHOWS MVFR STRATUS SOUTH  
OF THE KSLE/KONP LINE. NORTH OF THIS LINE VFR CONDITIONS ARE  
PRESENT. AREAS SOUTH OF THE KSLE/KONP LINE ARE SHOWING  
IMPROVEMENT FROM MVFR TO VFR, THE EXCEPTION BEING KEUG AND KONP.  
EXPECT MVFR CIGS ALONG THE COAST AFTER 06Z TUESDAY, AND INLAND  
LOCATIONS AFTER 12Z TUESDAY. AREAS AROUND AND INCLUDING KEUG AND  
KHIO COULD SEE SOME PATCHY MVFR/IFR VISIBILITIES AFTER 08Z  
TUESDAY. AFTER 20Z TUESDAY VFR CONDITIONS ARE EXPECTED TO  
PREVAIL.  
 
PDX AND APPROACHES...VFR WITH CALM WINDS THROUGH THE OVERNIGHT  
HOURS. THERE IS A CHANCE FOR A BRIEF PERIOD OF MVFR CIGS TO  
DEVELOP AFTER 16Z TUESDAY. EXPECT VFR TO RETURN AFTER 20Z  
TUESDAY IF THE MVFR CIGS DEVELOP. /42  
 

 
   
MARINE
 
HIGH PRESSURE SLOWLY BUILD ACROSS THE WATERS TONIGHT,  
AND WILL STRENGTHEN THROUGH TUESDAY. THIS STRENGTHENING WILL  
TIGHTEN UP THE PRESSURE GRADIENT, MAINTAINING THE PRESENT  
NORTHERLY WINDS OF 10 TO 15 KT, BUT WILL ALSO PRODUCE GUSTS UP TO  
25 KT THROUGH THE MIDDLE OF THE WEEK.  
 
SEAS REMAIN AROUND 6 TO 7 FT AND THE DOMINATE PERIOD OF 7  
SECONDS THROUGH THE OVERNIGHT HOURS. THEREFORE HAVE ISSUED A  
SMALL CRAFT ADVISORY FOR SQUARE SEAS THROUGH MONDAY NIGHT. SEAS  
ARE EXPECTED TO FALL BELOW 6 FEET BY TUESDAY BUT, A CHANCE  
REMAINS THAT THE SMALL CRAFT ADVISORY WILL GET EXTENDED INTO  
TUESDAY IF THE SQUARE SEAS CONTINUE TO PERSIST. /42  
 

 
   
PQR WATCHES/WARNINGS/ADVISORIES
 
 
OR...NONE.  
WA...NONE.  
PZ...SMALL CRAFT ADVISORY UNTIL 11 PM PDT THIS EVENING FOR COASTAL  
WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 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 NM OFFSHORE. THIS AREA IS COMMONLY  
REFERRED TO AS THE FORECAST AREA.  
 
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