Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 190842
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND
141 AM PDT SUN APR 19 2015

.SYNOPSIS...SUNNY AND WARM WEATHER IS EXPECTED THROUGH MONDAY AS HIGH
PRESSURE DOMINATES THE PACIFIC NORTHWEST. TEMPERATURES WILL WARM UP A
BIT EACH DAY...WITH SOME INLAND AREAS REACHING OR EXCEEDING 80
DEGREES. AN UPPER TROUGH MAY BRING COOLER CONDITIONS TUESDAY AND
WEDNESDAY WITH SOME SHOWERS. UNSETTLED WEATHER AND COOLER
TEMPERATURES WILL CONTINUE THROUGH NEXT WEEKEND.
&&

.SHORT TERM...TODAY THROUGH WEDNESDAY...A REX BLOCK IS TRYING TO FORM
OVER EAST PACIFIC AS WATER VAPOR IMAGERY SHOWS A LARGE UPPER RIDGE
OVER THE WEST CANADIAN COAST AND AN UPPER LOW OFFSHORENORTHERN
CALIFORNIA. THIS BLOCKING PATTERN WILL SLOWLY MOVE EASTWARD THE NEXT
SEVERAL DAYS SUCH THAT AN UPPER RIDGE WILL SUPPORT A WARMING AIRMASS
FOR THE PACIFIC NORTHWEST.

AT THE SURFACE...HIGH PRESSURE HOLDS EAST OF THE CASCADES AND OVER
THE NE PACIFIC. A THERMAL TROUGH HAS SHIFTED OFF OF THE OREGON COAST
OVERNIGHT SUCH THAT WEAK EASTERLY WINDS ARE DEVELOPING ACROSS NW
OREGON AND SW WASHINGTON EARLY THIS MORNING. THESE WINDS SHOULD HELP
KEEP THE COAST CLEAR OF LOW CLOUDS AND FOG THIS MORNING. A DRY
AIRMASS SHOULD PREVENT FOG FROM DEVELOPING IN THE AREAS WHERE THE
WINDS ARE CALM.

ANOTHER UNSEASONAL WARM DAY IS IN STORE FOR THE PORTLAND FORECAST
AREA. TEMPERATURES SHOULD BE A COUPLE OF DEGREES WARMER THAN
YESTERDAY WITH MANY WILLAMETTE VALLEY LOCATIONS REACHING OR GETTING
CLOSE TO 80 DEGREES. THE WEAK OFFSHORE WINDS WILL ALLOW COASTAL
TEMPERATURES TO WARM TOO WITH THE GREATEST WARMING FOR THE SOUTH
WASHINGTON AND NORTHERN OREGON COAST. THE THERMAL TROUGH WILL WEAKEN
THIS AFTERNOON AS IT SLOWLY MOVES INLAND...RESULTING IN WEAKER
NORTHERLY WINDS THROUGH THE WILLAMETTE VALLEY...AND A BETTER CHANCE
FOR THE SOUTHERN WILLAMETTE VALLEY TO WARM INTO THE UPPER 70S.

THE SURFACE PRESSURE GRADIENT WILL WEAKEN OVERNIGHT...AND WINDS WILL
BE LIGHT AND VARIABLE. THE DRY AIRMASS SHOULD PREVENT FOG FROM
FORMING TONIGHT DESPITE THE LOSS OF MIXING. THE UPPER RIDGE WILL BE
CENTERED OVER THE FORECAST AREA MONDAY AFTERNOON...WITH THE
THERMALLY-INDUCED SURFACE LOW AXIS OVER THE WILLAMETTE VALLEY. THIS
WILL RESULT IN A COUPLE DEGREES OF ADDITIONAL WARMING INLAND MONDAY.
MODELS ACTUALLY SHOW 850 MB TEMPS STARTING TO COOL MONDAY
AFTERNOON...BUT WITH A SLIGHTLY WARMER START WOULD EXPECT THAT TO
COUNTERACT THE 850MB COOLING TREND. ANOTHER THING TO CONSIDER FOR
MONDAY IS HOW MUCH DRIFT SMOKE ALOFT WILL BE OVER THE AREA. THE
FORECAST ASSUMES THE SMOKE ALOFT WILL HAVE SIMILAR OPAQUENESS TO WHAT
IT CURRENTLY HAS.

THE MARINE LAYER WILL DEEPEN MONDAY NIGHT AS AN UPPER TROUGH
APPROACHES. THE SURFACE WINDS WILL TURN MORE ONSHORE AND EXPECT
MARINE STRATUS TO DEVELOP ALONG THE COAST...PUSHING INLAND TUESDAY
MORNING. DRIZZLE MAY ACCOMPANY THE STRATUS ALONG THE COAST. THIS
MARINE PUSH WILL RESULT IN COOLER DAYTIME TEMPERATURES FOR TUESDAY
AFTERNOON....BUT THEY WILL STILL BE ABOVE THE SEASONAL NORMALS.

INSTABILITY ASSOCIATED WITH THE TROUGH MAY GENERATE A COUPLE OF
SHOWERS OVER THE MOUNTAINS TUESDAY AFTERNOON. THE MARINE
LAYER SHOULD SEVERELY LIMIT THE POTENTIAL FOR DEEP CONVECTION ACROSS
SW WASHINGTON AND NW OREGON EXCEPT RIGHT ALONG THE CASCADE CREST...
WHERE SURFACE PARCELS WILL START ABOVE THE MARINE INVERSION.

THE UPPER TROUGH WILL MOVE OVER THE AREA TUESDAY NIGHT AND WEDNESDAY
WITH A CHANCE FOR SHOWERS. WEDNESDAY WILL BE NOTICEABLY COOLER WITH
TEMPERATURES BACK TO SEASONAL NORMALS. TJ

.LONG TERM...WEDNESDAY NIGHT THROUGH SATURDAY...A SHORTWAVE RIDGE
WILL RESULT IN A BRIEF DRY PERIOD WEDNESDAY NIGHT AND THURSDAY.
MODELS ARE IN FAIR AGREEMENT THAT A WEAK FRONT WILL MOVE OVER THE
AREA THURSDAY. THE MODELS HAVE BEEN PROGRESSIVELY WEAKER WITH THIS
FRONT THE LAST COUPLE OF MODEL RUNS...AND AM LESS CONFIDENT ON RAIN
CHANCES WITH THIS FRONT. AN UPPER LEVEL LOW WILL DEVELOP OVER THE NE
PACIFIC FRIDAY AND SATURDAY UNDERSOLD IN UNSETTLED WEATHER FOR THE
WEEKEND. TJ
&&

.AVIATION...CLEAR AND DRY UNDER DRY STABLE NW FLOW ALOFT. WILL
AGAIN SEE PATCHY FOG IN THE COASTAL VALLEYS AND BAYS WHERE WINDS
ARE LIGHT THIS AM. SHOULD BURN OFF BETWEEN 15Z AND 17Z.

KPDX AND APPROACHES...CLEAR AND DRY UNDER HIGH PRES. NO WEATHER
IMPACTS EXPECTED THROUGH MON. ROCKEY
&&

.MARINE...NOT MUCH CHANGE. HIGH PRES REMAINS ANCHORED OVER THE
NE PAC AND INLAND PAC NW...WHILE THERMAL LOW PRES SITS OVER NW
CALIF. THIS WILL MAINTAIN GUSTY N WINDS ON THE COASTAL WATERS. THE
STRONGEST WINDS WILL BE OVER THE CENTRAL OREGON WATERS SOUTH OF
CASCADE HEAD...WHERE GUSTS OF 25 TO 30 KT WILL CONTINUE. WINDS
WILL BE LIGHTER NORTH OF CASCADE HEAD...WITH GUSTS 20 TO 25 KT.
THE WINDS STRONGEST THIS AFTERNOON INTO THIS EVENING.

WHILE BASE SWELL RUNNING AT 6 TO 7 FT...THE WINDS ARE CREATING
SOME CHOP AND BUILDING SEAS TO 8 TO 9 FT...ALTHOUGH THESE MAY
TOUCH CLOSE TO 10 FT FROM AROUND FLORENCE SOUTHWARD TODAY.

THE NEXT FRONT WILL MOVE THROUGH THE WATERS ON TUE. THEN THE
LONGER RANGE SHOWS HIGH PRES OVER THE NE PAC STRENGTHENING DURING
THE MIDDLE OF NEXT WEEK..WITH NW WINDS GUSTING 20 TO 30 KT AT
TIMES. ALSO EXPECT INCREASING NW SWELL TO PUSH SEAS BACK INTO THE
LOW TO MID TEENS STARTING WED.ROCKPYLEBONK
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS THROUGH MON AM ON ALL WATERS.
     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR
 CONDITIONS UNTIL 8 AM TODAY.
&&
$$

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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