Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 010352
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
843 PM PDT MON AUG 31 2015

.SYNOPSIS...A COLD FRONT WILL PUSH SOUTHEASTWARD ACROSS THE REGION
TUESDAY BRINGING A CHANCE OF RAIN WITH THE HIGHEST CHANCES ALONG THE
COAST...ACROSS SOUTHWEST WASHINGTON AND IN THE CASCADES. AN UPPER
LEVEL TROUGH OF LOW PRESSURE WILL LINGER OVER THE REGION THROUGH AT
LEAST THE END OF THE WORK WEEK...BRINGING A THREAT OF SHOWERS EACH
DAY. WARMER DRIER WEATHER LOOKS TO RETURN LATER IN THE WEEKEND.


&&


.UPDATE...WATER VAPOR SATELLITE IMAGERY REVEALS A WELL DEFINED
SHORTWAVE TROUGH DIVING SOUTHEASTWARD TOWARDS THE PACIFIC NORTHWEST.
AHEAD OF THIS FEATURE LIES A WEAK LOW LEVEL FRONT THAT WILL PUSH
SOUTHEASTWARD ACROSS THE AREA ON TUESDAY. VISIBLE SATELLITE IMAGERY
EARLIER THIS EVENING DID NOT MAKE THIS FRONT LOOK ALL THAT IMPRESSIVE
GIVEN THE BROKEN NATURE OF THE CLOUD COVER. NONETHELESS...A DISTINCT
LOW LEVEL BOUNDARY SHOULD RESULT IN SOUTH WINDS PICKING UP A BIT
AHEAD OF THE FRONT ALONG THE COAST...BEFORE TURNING NORTHWESTERLY AND
WEAKENING AFTER FRONTAL PASSAGE ON TUESDAY. THIS LOW LEVEL
CONVERGENCE SHOULD RESULT IN SOME SHOWERS PUSHING ONTO THE COAST
LATER TONIGHT AND TUESDAY...BEFORE A FEW OF THEM INTO THE WILLAMETTE
VALLEY AND CASCADES TUESDAY AFTERNOON AND EVENING. MOISTURE
AND INSTABILITY WILL BE SOMEWHAT LIMITED WITH THIS FRONT SO KEPT POPS
GENERALLY IN THE 40 TO 60 PERCENT RANGE ACROSS THE WILLAMETTE VALLEY
WHERE ANY GIVEN LOCATION IS CERTAINLY NOT GUARANTEED TO END UP WET
TOMORROW. RAIN CHANCES AND QPF GENERALLY LOOKS TO BE HIGHER ACROSS
THE NORTH...AND LOWEST TOWARDS LANE COUNTY DUE TO THE FRONT
WEAKENING. SHOWERS SHOULD GENERALLY BECOME MORE CONFINED TO THE COAST
AND HIGHER TERRAIN TUESDAY NIGHT AS LOW LEVEL INSTABILITY IS SOMEWHAT
LIMITED. THE MAIN UPPER LEVEL TROUGH AND COLD POOL ALOFT WILL
GRADUALLY SETTLE INTO THE PACIFIC NORTHWEST LATE WEDNESDAY AND
THURSDAY. MODELS CONTINUE TO STRUGGLE WITH THE TIMING OF INDIVIDUAL
SHORTWAVE TROUGHS AND VORT MAXES ROTATING INTO THE PACIFIC NORTHWEST
SO THE CURRENT FORECAST REMAINS PRETTY GENERIC AT THIS POINT...MAINLY
EMPHASIZING RAIN CHANCES APPEAR HIGHEST ACROSS OUR NORTHERN ZONES AND
DURING THE AFTERNOON AND EVENING HOURS EACH DAY.

CLIMATE FACTOID...GIVEN THE HIGH AND LOW TEMPERATURES OBSERVED SO FAR
TODAY AND NO DRASTIC TEMPERATURE CHANGES ARE EXPECTED IN THE NEXT
COUPLE OF HOURS...2015 WILL GO DOWN AS THE WARMEST METEOROLOGICAL
SUMMER...JUNE...JULY AND AUGUST...ON RECORD FOR PORTLAND...SALEM AND
EUGENE. RECORDS GO BACK APPROXIMATELY 120 YEARS FOR EUGENE AND
SALEM...AND 75 YEARS FOR PORTLAND. WILL PUT A GRAPHIC COMPARING THIS
YEAR TO THE PREVIOUS RECORDS ON OUR SOCIAL MEDIA SITES HOPEFULLY
BEFORE 10 PM. LINKS TO OUR SOCIAL MEDIA SITES CAN BE REACHED AT THE
BOTTOM OF THE AFD OR IN THE UPPER RIGHT HAND CORNER OF OUR HOMEPAGE.
/NEUMAN


.LONG TERM...THURSDAY NIGHT THROUGH MONDAY. LOWER CONFIDENCE THAN
NORMAL IN THE EVOLUTION OF THE EXTENDED PORTION OF THE FORECAST
TODAY GIVEN SOME KEY DIVERGENCES IN MODEL GUIDANCE BY THE WEEKEND.
OVERALL...A SLIGHTLY MORE AMPLIFIED AND MORE SLOWLY EVOLVING PATTERN
EXPECTED AS THE UPPER TROUGH REMAINS OVER THE PACIFIC NW ON FRIDAY.
DETERMINISTIC 12Z RUNS OF GFS AND ECMWF BOTH SLOW THE PROGRESS OF
THE UPPER TROUGH..AND HAVE THUS INCREASED POPS FRIDAY AND FRIDAY
NIGHT. BY SATURDAY...MODEL DIFFERENCES INCREASINGLY PROMINENT...WITH
THE ECMWF DEVELOPING A CLOSED UPPER LOW OVER WESTERN OREGON THROUGH
MUCH OF THE WEEKEND. THE ECMWF ENSEMBLE MEAN ALSO SUPPORTS THIS
SOLUTION...BUT A NON TRIVIAL NUMBER OF MEMBERS SEEM TO BE IN LINE
WITH THE GFS AND SLIGHTLY RISING HEIGHTS UNDER WEAK SHORTWAVE
RIDGING. FOR THIS REASON...KEPT THE FORECAST DRY AND WARMER WITH MAX
TEMPS AROUND SEASONAL NORMALS FOR SUNDAY AND MONDAY FOR NOW...BUT IF
THE ECMWF TREND IS CORRECT...SUNDAY MAY BE A COOLER AND PERHAPS
SHOWERY DAY.   CULLEN


&&


.AVIATION...WIDESPREAD VFR CONDITIONS WITH CIGS AROUND 5K-6K FT
THIS EVENING. AN APPROACHING COLD FRONT WILL LOWER CONDITIONS
OVERNIGHT...WITH THE COAST LIKELY SEEING IFR CONDITIONS LATE
TONIGHT INTO EARLY TUESDAY MORNING AS WELL AS GUSTY SOUTH WINDS UP
TO 25 KT. THE COAST SHOULD IMPROVE TO MVFR MID MORNING. EXPECT
INLAND AREAS TO REMAIN CLOUDY WITH VFR CONDITIONS THROUGH TUE
MORNING...WITH BRIEF MVFR CIGS AROUND 3500 FT POSSIBLE.

KPDX AND APPROACHES...CLOUDY WITH VFR CONDITIONS THROUGH TUE
MORNING. CIGS WILL REMAIN BETWEEN 4500-6000 FT. TJ/27


&&


.MARINE...SOUTH WINDS HAVE FINALLY EASED BELOW 20 KT THIS
EVENING...BUT THERE MAY BE SOME LOCALIZED SMALL CRAFT GUSTS AHEAD
OF AND WITH THE NEXT FRONTAL PASSAGE LATE TONIGHT THROUGH TUE
AFTERNOON...BUT DO NOT ANTICIPATE THE HIGHER GUSTS WILL BE
WIDESPREAD OR CONSISTENT ENOUGH TO WARRANT AN ADVISORY. SEAS WILL
REMAIN RELATIVELY STEEP TONIGHT WITH 7 TO 8 FT HEIGHTS AT 10 TO
11 SECONDS. A SURFACE LOW OVER THE GULF OF ALASKA...JUST OFFSHORE
OF YAKUTAT IS GENERATING A NORTHERLY FETCH THAT WILL BRING A BRIEF
PERIOD OF 10 FT SWELL TO THE OREGON WATERS WEDNESDAY.

SURFACE HIGH PRESSURE WILL BUILD OVER THE NE PACIFIC WED NIGHT
AND THU AS A THERMAL LOW DEVELOPS OVER NORTHERN CALIFORNIA. THIS
WILL BRING A RETURN OF NORTHERLY WINDS TO THE WATERS THURSDAY AND
FRIDAY. A LOW TO THE NORTH WILL PREVENT A TIGHT GRADIENT AND
EXPECT BELOW ADVISORY WINDS THU AND FRI. TJ


&&


.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 10
     PM PDT THIS EVENING...FROM 4 AM TO 9 AM PDT TUESDAY...AND
     FROM 5 PM TO 10 PM PDT TUESDAY.

&&

$$

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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