Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 250911
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND
212 AM PDT MON MAY 25 2015

.SYNOPSIS...AN UPPER LEVEL LOW IN SOUTHERN B.C. WILL SLOWLY MOVE
INTO EASTERN WASHINGTON MONDAY AND INTO IDAHO LATER TUESDAY AND
WEDNESDAY. THIS WILL MAINTAIN THE LOW LEVEL ONSHORE FLOW ACROSS
SOUTHWEST WASHINGTON AND NORTHWEST OREGON FOR THE NEXT SEVERAL DAYS
WITH LITTLE CLEARING IN THE AFTERNOONS. IT WILL ALSO PROVIDE THE
POSSIBILITY OF SOME NIGHT AND MORNING DRIZZLE OVER THE AREA...AS
WELL AS A FEW LATE DAY SHOWERS OR EVEN A THUNDERSTORM IN THE HIGHER
CASCADES. AN UPPER LEVEL RIDGE WILL MOVE INTO THE PACIFIC NORTHWEST
DURING THE SECOND HALF OF THE WEEK...WEAKENING THE ONSHORE FLOW AND
ALLOWING MORE SUNSHINE TO BREAK THROUGH WITH TEMPS WARMING ABOVE
NORMAL. SOUTHWEST FLOW ALOFT NEXT WEEKEND MAY BRING A RETURN TO THE
MARINE LAYER AND POSSIBLY A FEW THUNDERSTORMS OVER THE CASCADES
AGAIN.
&&

.SHORT TERM...MARINE AIR MASS REMAINED OVER NW OREGON AND SW WA
EARLY THIS MORNING. SURFACE OBSERVATIONS SHOWED A LITTLE DRIZZLE HAS
BEEN REPORTED NEAR THE N OREGON AND S WA COAST...BUT SO FAR WAS NOT
WIDESPREAD. AN UPPER LEVEL LOW WAS SEEN IN WATER VAPOR PICTURES
MOVING SE OVER SOUTHERN BC. THIS LOW IS EXPECTED TO MOVE SLOWLY SE
INTO EASTERN WA TODAY...AND EVENTAULLY INTO IDAHO BY WED. A MORE
WESTERLY ONSHORE FLOW THIS MORNING ACROSS THE N PART OF THE FORECAST
AREA WILL TEND TO MAKE FOR A MORE PERSISTENT MARINE CLOUD LAYER IN
THE N TODAY. OTHERWISE EXPECT A PATTERN TO CONTINUE THROUGH TUE WITH
CLOUDS REMAINING ALONG THE COAST...AND SOME BREAKS IN THE CLOUDS
LATE IN THE DAY INLAND. AS THE UPPER LOW PASSES BY TO THE NE...WILL
KEEP A MENTION OF NIGHTTIME AND MORNING DRIZZLE FOR THE N PART OF
THE FORECAST AREA...AND A SLIGHT CHANCE FOR SHOWERS OR THUNDERSTORMS
OVER THE S WA CASCADE WHERE INSTABILITY WITH BE BEST DUE TO COOL
POOL ALOFT.

BY WED THE UPPER LOW IS EXPECTED TO MOVE E INTO IDAHO...AS A RIDGE
OF HIGH PRES OFFSHORE PUSHES CLOSER TO THE COAST. THIS WEAKENS THE
ONSHORE FLOW A BIT...MAKING THE LIKELIHOOD OF CLOUDS BREAKING UP IN
THE AFTERNOON GREATER. THIS WILL ALLOW TEMPS TO WARM SOME,,,TO
SEVERAL DEGREES ABOVE NORMAL INLAND WED. WILL NEED TO KEEP A SLIGHT
CHANCE FOR AFTERNOON THUNDERSTORMS ALONG THE CASCADES WED A MORE
UNSTABLE WRAPS AROUND THE DEPARTING UPPER LOW.

.LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS. WEDNESDAY
NIGHT THROUGH SUNDAY...A WEAK RIDGE BUILDS OVER THE PACNW
MIDWEEK...DRYING OUT THE REGION. CONTINUED WEAK ONSHORE FLOW WILL
CONTINUE TO BRING MARINE CLOUDS INLAND OVERNIGHT...BUT STRATUS
SHOULD FOR THE MOST PART CLEAR OUT BY MIDDAY ALLOWING TEMPERATURES
TO REACH INTO THE UPPER 70S AND MAYBE LOW 80S INLAND. A THERMAL LOW
DEVELOPS IN NORTHERN CALIFORNIA ON THURSDAY AND STARTS TO PUSH
NORTHWARD ON FRIDAY AND SATURDAY...WHICH COULD HELP DEVELOP SOME
AFTERNOON SHOWERS AND MAYBE A FEW THUNDERSTORMS ALONG THE CREST OF
THE CASCADES ON FRIDAY THROUGH SUNDAY. BACKGROUND FLOW WILL BE OUT
OF THE WEST-NORTHWEST THOUGH...WHICH SHOULD KEEP THESE STORMS FROM
DRIFTING WESTWARD INTO THE VALLEY. -MCCOY &&

.AVIATION...EXPECT MVFR CIGS INLAND WITH SPOTTY IFR CIGS AT THE
COAST THIS MORNING. CIGS SHOULD GRADUALLY LIFT THROUGH THE MORNING
BUT STILL LEAVE THE NORTH OREGON COAST UNDER MVFR CIGS WHILE THE
CENTRAL COAST MAY BREAK OUT AGAIN. ONSHORE FLOW WILL AGAIN WEAKEN
SLIGHTLY TODAY ALLOWING DECENT POTENTIAL FOR THE INLAND AREAS TO
BREAK OUT FROM UNDER THE MARINE LAYER FOR SEVERAL HOURS. EXPECT TO
SEE CLOUDS FILL BACK IN WITH A 035 TO 045 AGL LAYER AFTER 26/03Z
BEFORE GRADUALLY DROPPING TO A MVFR LAYER OVERNIGHT.

KPDX AND APPROACHES...CIGS 025 TO 030 WILL PREVAIL UNTIL AROUND
18Z. THEN EXPECT LOW END VFR CIGS TO LIFT FURTHER AND SCATTER OUT
CLOSER TO 21Z. CIGS REDEVELOP AROUND 035 NEAR 26/03Z THEN
GRADUALLY LOWER TO MVFR OVERNIGHT. /JBONK

&&

.MARINE...NO SIGNIFICANT CHANGES MADE. PREVIOUS DISCUSSION
FOLLOWS. HIGH PRES CONTINUES TO REMAIN OFFSHORE WITH LOW PRES
OVER THE INLAND PAC NW FOR THE NEXT SEVERAL DAYS. EXPECT MILD
CONDITIONS OVER THE WATERS WITH NW WINDS GENERALLY BELOW ADVISORY
CRITERIA. THERE MAY BE BRIEF PERIODS OF ISOLATED ADVISORY GUSTS
ABOVE 21 KT SOUTH OF NEWPORT ONCE AGAIN MONDAY AFTERNOON/EVENING.
HOWEVER...DO NOT THINK THEY WILL BE WIDESPREAD ENOUGH TO WARRANT
ISSUING AN ADVISORY. MIXED SEAS WILL CONTINUE THROUGH MOST OF THIS
WEEK...WITH CHOPPY CONDITIONS EXPECTED AT TIMES DUE TO A FRESH NW
SWELL. /64

&&

.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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