Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 152228 CCB
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
320 PM PDT MON SEP 15 2014

.SYNOPSIS...SMOKE FROM THE 36 PIT WILDFIRE WILL IMPACT MOST OF NW
OREGON AND SW WASHINGTON THROUGH TONIGHT. AN UPPER LEVEL TROUGH WILL
BRUSH THE REGION TONIGHT...POSSIBLY TRIGGERING SOME DRY
THUNDERSTORMS OVER THE AREA...BUT CONFIDENCE IS LOW. THIS TROUGH
WILL ALSO BRING A RETURN OF LOW MARINE CLOUDS TO THE AREA...AND HELP
COOL TEMPERATURES FOR TUESDAY. A WEAKENING STORM SYSTEM WILL BRING A
CHANCE FOR RAIN SHOWERS LATE WEDNESDAY INTO EARLY THURSDAY. HIGH
PRESSURE WILL LIKELY REBUILD FRIDAY WITH DRY AND WARMER CONDITIONS
RETURNING NEXT WEEKEND.

&&

.SHORT TERM...WATER VAPOR SATELLITE IMAGERY THIS AFTERNOON REVEALS A
NEGATIVELY TILTED SHORTWAVE TROUGH OFF THE NORTHERN CALIFORNIA COAST
LIFTING NORTH-NORTHEASTWARD TOWARDS THE FORECAST AREA. STRONG LIFT
AHEAD OF THIS SHORTWAVE TROUGH IS RESULTING IN MID TO UPPER LEVEL
CLOUDS STREAMING NORTHEASTWARD ACROSS THE AREA.

OVER THE PAST COUPLE OF DAYS...MODEL SOUNDINGS HAVE SUGGESTED THERE
WAS A CHANCE FOR ELEVATED THUNDERSTORMS TO DEVELOP TONIGHT. BASED ON
SATELLITE EXTRAPOLATION AND LATEST MODEL SOUNDINGS...THUNDER CHANCES
CONTINUE TO APPEAR LESS FAVORABLE FOR DEVELOPMENT. GIVEN THE
INHERENT UNCERTAINTY IN FORECASTING ELEVATED CONVECTION...WILL
CONTINUE TO KEEP THE MENTION OF DRY THUNDER IN THE FORECAST GIVEN
THE SYNOPTIC PATTERN.

A WIND REVERSAL IS CURRENTLY PUSHING NORTHWARD UP THE
COAST...AHEAD OF SCHEDULE...WHICH IS NOT ATYPICAL. SURFACE ANALYSIS
SUGGESTS THE THERMAL TROUGH CURRENTLY LIES DIRECTLY OVER THE
WILLAMETTE VALLEY...WITH SURFACE HIGH PRESSURE BUILDING NORTHWARD UP
THE COAST. PRESSURE GRADIENTS SHOULD SUPPORT A DECENTLY STRONG
SOUTHWEST MARINE PUSH...WHICH OFTEN RESULTS IN MARINE CLOUDS SPILLING
INTO THE WILLAMETTE VALLEY. AS A RESULT...SKY COVER WAS TRENDED
TOWARDS THE IDEA OF MORNING CLOUDS GIVING WAY TO LATE AFTERNOON
SUNSHINE. HOWEVER...RAW MODEL AND MOS GUIDANCE IS NOT TOO KEEN ON
THIS IDEA SO UNCERTAINTY EXISTS.

ALSO OF CONCERN ARE THE AREAS OF SMOKE ACROSS THE WILLAMETTE VALLEY
AND SOUTHWEST WASHINGTON THIS AFTERNOON DUE TO THE 36 PIT FIRE
BURNING SOUTHEAST OF ESTACADA OREGON. VISIBILITY WILL CONTINUE TO BE
IMPACTED IN THE WILLAMETTE VALLEY...BUT IS NOT EXPECTED TO DROP LOW
ENOUGH TO WARRANT A DENSE SMOKE ADVISORY. NONETHELESS...AIR QUALITY
ISSUES EXIST SO SEE THE SPECIAL WEATHER STATEMENT ISSUED EARLIER
TODAY FOR ADDITIONAL INFORMATION. SOUTHWEST WINDS SPILLING THROUGH
THE COAST RANGE GAPS ACROSS THE SOUTHERN AND CENTRAL WILLAMETTE
VALLEY SHOULD HELP TO CLEAR OUT SOME OF THE SMOKE TONIGHT. STRONGER
WESTERLY FLOW TUESDAY SHOULD ALSO ASSIST IN MOST SMOKE SPREADING
EASTWARD AWAY FROM THE WILLAMETTE VALLEY. NONETHELESS...LIGHT DOWN
VALLEY WINDS WILL LIKELY ALLOW THICK SMOKE AND AIR QUALITY ISSUES TO
PERSIST IN NEARBY TOWNS LIKE ESTACADA.

A SHORTWAVE TROUGH CURRENTLY NEAR 140W AND 35N WILL APPROACH THE WEST
COAST WEDNESDAY INTO THURSDAY. MODELS CONTINUE TO WAVER ON THE
DETAILS WITH THIS SYSTEM AS THE UPPER LEVEL LOW PRESSURE TRIES TO
SPLIT FROM THE MEAN FLOW AND DIVE INTO THE DESERT SOUTHWEST. AS OF
NOW...THE MAIN GLOBAL MODELS...THE GFS AND EC...SUGGEST AT LEAST
SOME LIGHT RAIN SHOWERS ARE LIKELY ACROSS THE AREA LATE WEDNESDAY
INTO EARLY THURSDAY. HOWEVER...GIVEN THE SPLITTY NATURE OF THE
SYSTEM...AND THIS WILL BE THE FIRST SYSTEM TO MOVE INTO THE HIGH
PRESSURE IN QUITE SOME TIME...MODELS ARE LIKELY TOO AGGRESSIVE WITH
RAIN CHANCES FOR THE REGION. AS A RESULT...POPS WERE GENERALLY KEPT
IN THE 2O TO 50 PERCENT RANGE. WITH THAT SAID...THERE IS A BIT OF
ELEVATED INSTABILITY WEDNESDAY AFTERNOON AND EVENING ACROSS THE AREA
SO THERE IS A SLIGHT CHANCE FOR ELEVATED THUNDERSTORMS TO DEVELOP.
AT THIS POINT...THUNDER WORDING WAS PRIMARILY LIMITED TO THE CENTRAL
OREGON CASCADE FOOTHILLS AND MOUNTAINS.

ALL IN ALL...TEMPERATURES WILL REMAIN MUCH CLOSER TO NORMAL THIS WEEK
THAN IN RECENT DAYS. /NEUMAN


.LONG TERM...FRIDAY THROUGH MONDAY...GFS...DGEX...AND ECMWF ALL SHOW
A UPPER-LEVEL TROUGH OVER THE WEST COAST ON FRIDAY. THE SURFACE LOW
ASSOCIATED WITH THIS SYSTEM WILL MOVE ON-SHORE ON
FRIDAY...TRANSITIONING OUR AREA TO NORTHWESTERLY FLOW AT LOWER
LEVELS. THE COLD FRONT WILL THEN PROGRESS OFF TO THE NORTHEAST EARLY
SATURDAY ENDING CHANCES FOR RAINFALL LATE FRIDAY NIGHT. HIGH
PRESSURE LOOKS TO MOVE ONSHORE TO OUR NORTH ON SATURDAY BEHIND THE
FRONT...BRIEFLY BRINGING BACK EASTERLY WINDS WHICH WILL WARM
TEMPERATURES ON SATURDAY. THE MODELS ARE IN AGREEMENT THOUGH THAT A
WEAK...DRY FRONTAL BOUNDARY WILL MOVE THROUGH SUNDAY WHICH WILL
SERVE TO SHIFT WINDS BACK TO THE WEST OR SOUTHWEST. THE WESTERLY
COMPONENT WILL BRING IN MARINE AIR WHICH WILL SLIGHTLY COOL
TEMPERATURES SUNDAY AND MONDAY. -MCCOY

&&

.AVIATION...MOSTLY VFR CONDITIONS THIS AFTERNOON AND EVENING
EXCEPT FOR IFR MARINE CLOUDS ALONG THE IMMEDIATE COAST...AND
LOCALIZED MVFR CONDITIONS FROM SMOKE RELATED TO THE OREGON
WILDFIRES. THE LOW MARINE CLOUDS ARE CURRENTLY CONFINED TO THE
IMMEDIATE COAST...BUT ONSHORE WINDS LATER THIS AFTERNOON SHOULD
BRING IFR CONDITIONS TO THE ALL OF THE COASTAL AIRPORTS. CIGS
SHOULD LIFT LATE TONIGHT AS AN UPPER LOW BRUSHES BY WHICH WOULD
ALLOW THE MARINE CLOUDS TO PUSH FURTHER INLAND. THERE IS A LOT OF
UNCERTAINTY ON HOW FAR INLAND THEY WILL GO...BUT KCVO AND KEUG
ARE THE INLAND AIRPORTS WITH THE GREATEST CHANCE FOR LOW MVFR CIGS
AFT 10Z. DO NOT THINK FLIGHT RESTRICTING CLOUDS WILL MAKE IT IN TO
THE CENTRAL OR NORTHERN WILLAMETTE VALLEY. THE MARINE CLOUDS WILL
LIKELY STAY PARKED ALONG THE IMMEDIATE COAST THROUGH TUE...BUT ANY
LOW CLOUDS INLAND SHOULD CLEAR EARLY TUE AFTERNOON.

KPDX AND APPROACHES...HIGH CLOUDS WILL STREAM OVER THE AIRPORT
THROUGH TUE AFTERNOON...WITH VFR CONDITIONS DOMINATING. SMOKE MAY
CREATE
A SCATTERED CIG FROM 3 TO 5 KFT TONIGHT WHEN THE WINDS EASE AFT
05Z. TJ

&&

.MARINE...S-SW WINDS WILL PERSIST OVER THE WATERS THROUGH AT
LEAST WEDNESDAY. A WEAK LOW WILL BRUSH PAST THE WATERS THIS
EVENING. A STRONGER LOW WILL APPROACH FROM THE SW TUE AND DRAG A
WEAK FRONT ACROSS THE WATERS FROM SOUTH TO NORTH WED AND THU.

THESE LOWS ARE PRODUCING A COUPLE OF LONGER-PERIOD SW SWELLS THAT
WILL PROPAGATE THROUGH THE WATERS THIS WEEK. MEANWHILE...A SERIES
OF LOWS MOVING OVER THE GULF OF ALASKA WILL GENERATE NW SWELLS
THROUGH THE WATERS. THE DIFFERENT SWELL TRAINS WILL IMPACT THE
NORTHERN OREGON AND SW WASHINGTON WATERS SIMULTANEOUSLY TUE
THROUGH THU RESULTING IN SEAS FROM MULTIPLE DIRECTIONS.

HIGH PRESSURE WILL REBUILD OVER THE WATERS THU NIGHT AND FRI. A
THERMALLY INDUCED TROUGH WILL SET UP ALONG THE NORTHERN CALIFORNIA
COAST FRIDAY NIGHT AND NORTHERLY WINDS WILL RETURN TO THE OREGON
WATERS. THE NORTHERLY WINDS SHOULD PERSIST THROUGH NEXT WEEKEND.
THE SW SWELLS WILL DROP OFF BY THURSDAY AND A 5 TO 7 FT NW SWELL
WILL DOMINATE THROUGH THE WEEKEND. TJ

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...RED FLAG WARNING UNTIL MIDNIGHT TONIGHT FOR ZONE 602-ZONE
603- ZONE 604-ZONE 605-ZONE 606-ZONE 607-ZONE 608.

WA...RED FLAG WARNING UNTIL MIDNIGHT TONIGHT FOR ZONE 604-ZONE
660.

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 AS THE FORECAST AREA.



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