Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 280320
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
820 PM PDT WED AUG 27 2014

.SYNOPSIS...UPPER RIDGE THAT HAS BEEN RESPONSIBLE FOR THE WARM
WEATHER WILL WEAKEN AND SHIFT EASTWARD THU AND FRI. THIS WILL ALOW
FOR WESTERLY FLOW OFF THE N PAC TO ARRIVE...BRINGING COOLER AIR AND
EVEN A THREAT OF SHOWERS FOR THIS WEEKEND. DRY WEATHER RESUMES NEXT
WEEK...WITH MORE SEASONABLE TEMPERATURES FOR EARLY SEPTEMBER.
&&

.SHORT TERM...TONIGHT THROUGH SATURDAY...
NOT A LOT OF CHANGE THIS EVENING. THERMAL LOW PRES NOW SITS EAST OF
THE CASCADES...AND ONSHORE FLOW IS STARTING TO STRENGTHEN. LOW CLOUDS
AND AREAS OF FOG ARE RAPIDLY FILLING THE COASTAL BEACHES. THESE
CLOUDS AND FOG WILL PUSH FURTHER INLAND TO FILL MOST ALL COASTAL
VALLEYS BY LATER THIS EVENING.

AS THE UPPER HIGH PRES RIDGES CURRENTLY SITS OVER THE WESTERN
US...WITH LOW PRES OVER THE GULF OF ALASKA.  THIS HIGH WILL WEAKEN
AND SHIFT EASTWARD OVER NEXT FEW DAYS. THIS WILL ALLOW FOR INCREASING
WESTERLY FLOW ALOFT OVER THE N PAC TO PUSH INTO THE PAC
NW...RESULTING IN INCREASED ONSHORE FLOW AND COOLER TEMPERATURES. A
WEAK UPPER DISTURBANCE IN THE FLOW WILL APPROACH LATER TONIGHT AND
MOVE ACROSS REGION THU. MODELS HAVE SLOWED ITS ARRIVAL UNTIL MID DAY
THU...SO THIS WILL LIMIT AREAS OF DRIZZLE THU AM TO COAST AND INTO
THE COAST RANGE. WILL MODIFY EVENING UPDATED FORECAST TO REFLECT THIS
TREND. HOWEVER...SHOULD BE ENOUGH TO BRING MARINE CLOUDS INTO MOST OF
SW WASHINGTON AND OREGON COAST...AND INTO THE N WILLAMETTE VALLEY.
SUSPECT MARINE LAYER WILL GRADUALLY INCREASE THU AND TAKE SOME TIME
TO FILL THE INTERIOR SO MORNING LOW CLOUDS OVER N INTERIOR WILL BURN
OFF LATER THU AM...THEN SUNNY WITH INLAND TEMPS IN THE LOWER 80S.

ONSHORE FLOW WILL GET STRONGER THU NIGHT AND FRI AS THE LOW OVER THE
GULF OF ALASKA SHIFTS EASTWARD INTO BRITISH COLUMBIA AND THE PAC NW.
THIS WILL RESULT IN A STRONG MARINE PUSH THAT FILLS THE INTERIOR
VALLEYS WITH CLOUDS THAT WILL PERSIST ON FRI. THE LIFT ASSOCIATED
WITH THE DISTURBANCE DOES NOT APPEAR TO BE VERY IMPRESSIVE...BUT IT
MAY BE ENOUGH TO WRING OUT SOME DRIZZLE OVER PORTIONS OF THE FCST
AREA. THE BEST CHANCES APPEAR TO BE FOR THE COAST...COAST RANGE...AND
CASCADE FOOTHILLS. OTHERWISE...EXPECT A CLOUDY AND MUCH COOLER DAY
ACROSS THE REGION.

THE BASE OF THE UPPER LEVEL TROUGH MOVES ONSHORE SATURDAY. THIS WILL
MEAN MORE CLOUDS AND COOL TEMPS. AFTERNOON HIGHS ARE EXPECTED TO
REMAIN IN THE LOW TO MID 70S OVER THE INTERIOR. WITH THE DEEP MARINE
LAYER IN PLACE...AGAIN EXPECT A CHANCE FOR SOME SHOWERS OR
DRIZZLE...PARTICULARLY FOR THE COAST AND THE NORTHERNMOST PORTIONS OF
THE FORECAST AREA.  ROCKPYLE

.LONG TERM...ECMWF...GFS AND DGEX TODAY DRASTICALLY CUT BACK ON
MOISTURE OVER OUR CWA FOR THIS WEEKEND...AND REMOVED MOST OF THE
PRECIPITATION SOUTH OF THE COLUMBIA RIVER THROUGH MONDAY.  THIS GOES
WITH THE TREND AND CLIMATOLOGY OF TROUGHS FROM THE NORTHWEST THIS
TIME OF YEAR WHERE MOISTURE ISN`T SUFFICIENT FOR SIGNIFICANT
RAINFALL OVER MOST OF OUR AREA. I LEFT A CHANCE FOR RAIN OVER HIGHER
TERRAIN OVER THE OR COASTAL RANGE AND WA...BUT REDUCED POPS TO A
SLIGHT CHANCE ELSEWHERE OVER THE NORTHERN HALF AND DROPPED POPS
INLAND SOUTH. EARLY NEXT WEEK WEAK RIDGING LOOKS TO BUILD IN
INDICATING A WARMING TREND TOWARD CLIMATOLOGY. -MCCOY
&&

.AVIATION...IFR CLOUDS AND FOG NOW HUGGING THE COASTLINE...AND
WILL PUSH INLAND ALONG THE COASTAL VALLEYS THIS EVENING. STILL
SEEMS REASONABLE THAT ONSHORE FLOW IS STRONG ENOUGH TO PUSH
LOW MVFR OR IFR CLOUDS UP THE COLUMBIA RIVER...FILLING MOST OF
THE COWLITZ AND LOWER COLUMBIA VALLEYS. CLOUDS SHOULD FILTER
WELL INTO THE N WILLAMETTE VALLEY BETWEEN 12Z AND 18Z. CLOUDS
WILL BURN BACK TO THE COAST RANGE BY 18Z...BUT ONSHORE FLOW
WILL CONTINUE SO COAST LIKELY TO REMAIN IN CLOUDS THAT WILL
LIFT TO MVFR IN THE AM. EXPECT BREEZY W WINDS OVER HIGHER
TERRAIN AND IN EAST COLUMBIA GORGE AFTER 18Z THU.

EXPECT AREAS OF SMOKE IN EASTERN LANE COUNTY DUE TO WILDFIRES.

KPDX AND APPROACHES...VFR TONIGHT AND THU. BUT CONFIDENCE
GROWING FOR LOW MVFR OR IFR...WHERE CIGS 800 TO 1200 FT...
TO ARRIVE AT KPDX/KTTD AROUND 12Z...AND PERSIST UNTIL 18Z.
&&

.MARINE...NOT MANY CHANGES THROUGH THE FORECAST PERIOD DESPITE A
COUPLE OF WEAK FRONTS MAKING THEIR WAY THROUGH THE AREA THURSDAY AND
OVER THE WEEKEND. WINDS WILL REMAIN AROUND 10 KT OUT OF THE
NW...BRIEFLY SHIFTING W AND SW WITH EACH FRONTAL PASSAGE. NW SWELL
BUILDS SATURDAY NIGHT INTO SUNDAY WITH COMBINED SEAS UP TO 7 FT.
SEAS COULD BE A BIT STEEP WITH 8 TO 10 SECOND PERIODS BUT SHOULD
IMPROVE WITH FAVORABLE BOATING CONDITIONS FOR LABOR DAY. OTHERWISE
NO SIGNIFICANT IMPACTS IN THE FORECAST.
&&

.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. THE AREA IS
COMMONLY REFERRED TO AS THE FORECAST AREA.



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