Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 020409
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
849 PM PDT TUE SEP  1 2015

.SYNOPSIS...A COLD FRONT WILL SLOWLY MOVE SOUTHWARD INTO SOUTHWEST
WASHINGTON AND NORTHWEST OREGON OVERNIGHT. IT WILL BRING A LITTLE
LIGHT RAIN TO THE AREA. THE SOUTHERN PART OF THE ASSOCIATED TRAILING
UPPER LOW WILL SLOWLY EXTEND INTO SOUTHWEST WASHINGTON AND NORTHWEST
OREGON WEDNESDAY FOR MORE SHOWERS...AND LINGER OVER THE PACIFIC
NORTHWEST THURSDAY. ENERGY ON THE WEST SIDE OF THE UPPER LOW WILL
DROP DOWN ALONG THE COAST THURSDAY NIGHT THEN SWING INLAND MAINLY
SOUTH OF OUR FORECAST AREA FRIDAY. HOWEVER...THE COLDER AIR ALOFT
WILL BE MORE OVER OUR AREA FRIDAY FOR A GREATER CHANCE OF AFTERNOON
AND EVENING SHOWERS AND THUNDERSTORMS. THE LOW WILL MOVE OFF TO THE
EAST THIS WEEKEND FOR IMPROVING WEATHER...THOUGH ANOTHER SYSTEM IS
POSSIBLE EARLY NEXT WEEK.

&&

.UPDATE...SATELLITE INFRARED IMAGERY SHOWS THE UPPER PORTION OF THE
FRONT SHEARING AHEAD OF THE LOWER FRONT. THE SURFACE FRONT IS NOW
NEAR THE SOUTH WASHINGTON COAST AND IS FORECAST TO MOVE INLAND OVER
NIGHT. DO NOT EXPECT TOO MUCH RAIN OVERNIGHT AS THE SYSTEM SHEARS BUT
MORE CONVECTIVE SHOWERS ARE EXPECTED WED AFTERNOON AS A COOL TROUGH
SETTLES INTO THE AREA.NAM AND GFS MODEL SOUNDINGS HAVE DIFFERING
SOLUTIONS ON THE THERMAL PROFILE WITH THIS SYSTEM. THE GFS IS A
LITTLE MORE UNSTABLE OVERALL SO WILL HAVE TO WATCH. BUT WILL KEEP
THREAT OF THUNDER FOR NORTHERN COASTAL AND INLAND ZONES WED AFTERNOON
THROUGH WED EVENING.

PREVIOUS DISCUSSION
SHORT TERM...LIGHT RAIN IS DISSIPATING AS IT MOVES SLOWLY INLAND
EARLY THIS AFTERNOON. THE RAIN WHICH DROPPED ABOUT 0.25 INCHES AT
ASTORIA THIS MORNING IS NOW VERY LIGHT AND DO NOT THINK IT WILL MAKE
IT INTO THE VALLEY. BEHIND IT ARE SOME LIGHT TO MODERATE SHOWERS
WHICH ARE A BIT MORE SUCCESSFULLY MOVING INLAND AND WILL LIKELY BE
THE BEST SHOT FOR ANY INLAND RAIN. CONTINUED TO DIAL BACK POPS IN THE
VALLEY THROUGH THIS EVENING.

SHORTWAVES ROTATING AROUND AN UPPER LOW BEGIN TO ARRIVE TONIGHT AND
INTO WEDNESDAY...INCREASING RAIN CHANCES ACROSS THE LOCAL FORECAST
AREA. COMBO OF DAYTIME HEATING AND A DECENT SHORTWAVE WILL BRING A
SLIGHT THREAT OF THUNDER TO NORTHERN AREAS TOMORROW AFTERNOON WITH
SHOWERS ELSEWHERE. FREEZING LEVELS WILL BE DROPPING...BUT DO NOT
THINK IT WILL BE COLD ENOUGH TO GET SMALL HAIL WITH SHOWERS OR
THUNDERSTORMS.

THURSDAY AND FRIDAY ARE LOOKING DRIER AS THE UPPER TROUGH DIVES SOUTH
OF THE AREA. REMOVED THUNDER MENTION THURSDAY DUE TO MOST OF THE
FORCING BEING EAST OF THE AREA BY AFTERNOON. THUNDER STILL LOOKS
POSSIBLE FRIDAY...BUT REALLY ONLY FOR THE CASCADES AND EVEN THEN
PROBABLY CLOSE TO THE CREST.

WITH UPPER TROUGH MOVING THROUGH...TEMPERATURES WILL BE A BIT COOLER
STARTING TOMORROW AND REMAIN BELOW NORMAL THROUGH AT LEAST THE END OF
THE WORKWEEK WITH HIGH TEMPERATURES AROUND 70 DEGREES INLAND AND 60
TO 65 ALONG THE COAST. INLAND LOW TEMPERATURES WILL ALSO BE
SIGNIFICANTLY MORE COMFORTABLE WITH LOWS WELL BELOW 60 DEGREES. BOWEN


.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY. BETTER AGREEMENT IN THE
FORECAST MODELS TODAY WITH RESPECT TO THE MOVEMENT OF THE UPPER
TROUGH THROUGH THE REGION. EXPECT THAT IT WILL CONTINUE TO ROTATE
THROUGH THE REGION AND EAST OF THE CASCADES BY LATE FRIDAY OR EARLY
SATURDAY. EVEN THE ECMWF...WHICH HAS BEEN SLOWER TO ADVANCE THE
TROUGH...ESTABLISHES MORE NORTHERLY FLOW ALOFT BY SATURDAY FOR
INCREASINGLY IMPROVING CONDITIONS. SUNDAY WILL BE DRY AND
WARMER...WITH MAXIMUM TEMPERATURES RETURNING TO AROUND SEASONAL
NORMALS...OR NEAR 80 FOR THE WILLAMETTE VALLEY. A WEAKENING BOUNDARY
MAY CLIP THE SW WASHINGTON ZONES MONDAY...BUT EXPECT ANY LIGHT
PRECIPITATION TO REMAIN OFFSHORE. ANOTHER LOW PRESSURE SYSTEM MAY
APPROACH THE REGION BY TUESDAY OR WEDNESDAY NEXT WEEK FOR ANOTHER
ROUND OF PRECIPITATION AND COOLER TEMPERATURES.  CULLEN

&&

.AVIATION...MOSTLY VFR CONDITIONS TONIGHT AND WEDNESDAY. THE
COAST MAY SEE BRIEF MVFR CIGS AND VSBYS DUE TO LIGHT RAIN OR MIST
THROUGH 16-18Z WED MORNING. INLAND SITES SHOULD NOT DROP LOWER
THAN A HIGH END MVFR AT WORST AND PROBABLY REMAIN VFR WITH CIGS
AROUND 050. SHOWERS WILL BE MORE CONVECTIVE WED AFTERNOON WITH
HEAVIER SHOWERS RESULTING IN A BETTER CHANCE FOR MVFR CONDITIONS.

KPDX AND APPROACHES...VFR ALTHOUGH CIGS LOWER TO 025-035 AFTER 14Z
WEDNESDAY AS A WEAK FRONT MOVES ONSHORE. TJ/27

&&

.MARINE...A WEAK TROUGH WILL MOVE OVER THE WATERS WED BEFORE
SURFACE HIGH PRESSURE BUILDS ON THURSDAY. LOW PRESSURE OVER
NORTHERN CA WILL RESULT IN NORTHERLY WINDS THU AFTERNOON THROUGH
THE WEEKEND. THE NORTH WINDS WILL INCREASE IN THE AFTERNOONS...
ESPECIALLY SOUTH OF LINCOLN CITY.

A SURFACE LOW OVER THE GULF OF ALASKA...JUST OFFSHORE OF THE DIXON
ENTRANCE IN ALASKA IS GENERATING LARGE SWELL ACROSS THE NE
PACIFIC THIS MORNING. SEAS FROM BUOYS UPSTREAM OF THE OREGON
WATERS SUGGESTS THAT THE ENP GUIDANCE IS UNDER-FORECASTING THIS
SWELL 1 TO 2 FT. HAVE THEREFORE WENT A LITTLE ABOVE GUIDANCE FOR
THIS SWELL AND EXPECT 10 TO 11 FT SEAS IN THE WATERS LATE WED
AFTERNOON AND EVENING. 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 6 AM TO 10 AM PDT WEDNESDAY...AND
     FROM 6 PM TO 10 PM PDT WEDNESDAY.

&&


$$

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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