Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 020350
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
849 PM PDT WED OCT  1 2014

.SYNOPSIS...NORTHWEST FLOW ALOFT ACROSS THE PACIFIC NORTHWEST
TONIGHT IN THE WAKE OF A RECENT LOW PRESSURE SYSTEM. AN UPPER RIDGE
WILL APPROACH THE COAST THURSDAY AND MOVE ONSHORE FRIDAY FOR DRY AND
WARMER WEATHER. WEAK OFFSHORE FLOW IS EXPECTED TO DEVELOP THURSDAY
AND CONTINUE INTO FRIDAY. THE RIDGE MAY WEAKEN ENOUGH OVER THE
WEEKEND TO ALLOW SOME LIGHT PRECIPITATION OVER THE SOUTH WASHINGTON
AND FAR NORTH OREGON COAST AND COAST RANGE.

&&

.UPDATE...VARIATIONS ON LIGHT NORTHERLY FLOW THIS EVENING AS RIDGE
AXIS REMAINS TO OUR WEST. WITH SKIES CURRENTLY MOSTLY CLEAR...EXPECT
FOG AND LOW STRATUS WILL DEVELOP OVERNIGHT BUT TIMING WILL DEPEND ON
HOW FAST TEMPERATURES DROP OFF. AS OF 8 PM DEWPOINT DEPRESSIONS ARE
RUNNING 8-10 DEGREES...SO IT`LL BE AT LEAST ANOTHER COUPLE OF HOURS
BEFORE FOG BEGINS TO FORM. FORECAST LOOKS IN GOOD SHAPE WITH PATCHY
FOG FROM ABOUT 06Z...SPREADING PARTICULARLY IN THE VALLEY THROUGH
MORNING. ASSUMING DEWPOINTS DROP A BIT AS EXPECTED...TONIGHT SHOULD
BE THE COOLEST SO FAR THIS FALL WITH MORNING LOWS RANGING FROM THE
UPPER 40S ALONG THE COAST AND IN THE WARMER PORTLAND METRO AREA DOWN
TO AROUND 40 DEGREES IN THE SOUTH WILLAMETTE VALLEY WITH SOME UPPER
30S IN THE OUTLYING VALLEYS. BOWEN

.SHORT TERM (PREVIOUS DISCUSSION)...THE CLOUD PATTERN FROM THIS
MORNING HAS ADJUSTED SOME BASED ON OVERTURNING FROM DAYTIME HEATING
AND ALSO FROM THE NORTHWEST FLOW OVER THE AREA. THE CLOUDS ARE MOST
SOLID IN THE NORTHERN FORECAST ZONES AND OVER THE NORTHERN CASCADE
AREAS AND A GOOD PART OF THE COAST RANGE. THE NORTHWEST FLOW WILL
PERSIST TONIGHT AS THE MAIN UPPER RIDGE AXIS REMAINS TO OUR WEST. THE
MODELS INDICATE THAT THERE MIGHT BE SOME BRIEF DECREASE IN THE CLOUDS
THIS EVENING WITH THE LOSS OF DAYTIME HEATING...BUT OVERNIGHT COOLING
WILL LEAD TO A THICKENING OF THE LOW CLOUDS ACROSS OUR NORTHERN
ZONES...AROUND PORTLAND NORTH...AND ESPECIALLY AROUND THE HIGHER
TERRAIN. IN AREAS THAT DO CLEAR TONIGHT...ESPECIALLY SOUTH OF
PORTLAND...WILL LIKELY SEE AREAS OF FOG AND LOW STRATUS REDEVELOP
LATE TONIGHT AND THURSDAY MORNING.

THE MODELS FORECAST A LIGHT OFFSHORE FLOW PATTERN DEVELOPING THURSDAY
AND FRIDAY...PARTLY DUE TO A SYSTEM PASSING WELL TO OUR NORTH INTO
MONTANA AND ITS TRAILING HIGHER PRESSURE TONIGHT AND THURSDAY
MORNING...AND DUE TO GOOD RADIATIONAL CONDITIONS THE NEXT COUPLE OF
DAYS THAT WILL LEAD TO A COOLER AIR MASS EAST OF THE CASCADES.
GRADIENTS WILL REMAIN VERY LIGHT TONIGHT AND EARLY THURSDAY. THE
MODELS SHOW MORE OF A NORTHERLY FLOW DEVELOPING DOWN THE VALLEY WITH
A LIGHT EAST FLOW IN THE GORGE ON THURSDAY. THE GRADIENT TURNS MORE
EASTERLY THURSDAY NIGHT AND FRIDAY AND THE EAST WIND THROUGH THE
GORGE WILL INCREASE THEN...WITH GUSTS TO 35 MPH OR SO POSSIBLE
AROUND CORBETT THURSDAY NIGHT THROUGH FRIDAY. THE OFFSHORE GRADIENT
DECREASES LATE FRIDAY.

THE COOL AIR MASS AND GOOD RADIATIONAL CONDITIONS WILL LEAD TO COOL
NIGHTTIME TEMPS THE NEXT FEW NIGHTS. THE MODELS FORECAST DEWPOINTS
STAYING IN THE LOWER 40S SO THIS MAY LIMIT HOW COOL WE DO GET...BUT
SOME UPPER 30S ARE POSSIBLE TONIGHT AND MID TO UPPER 30S THURSDAY
NIGHT.

A WEAK FRONT TRIES TO SAG INTO OUR NORTHERN COASTAL WATERS THIS
WEEKEND...BUT THE MODELS HAVE NOT BEEN VERY CERTAIN WITH THIS.
OTHERWISE THE REMAINDER OF THE AREA WILL SEE DRY AND MILD CONDITIONS
EXCEPT COOL IN THE MORNING WITH LOCAL MORNING FOG OR LOW CLOUDS
AROUND. TOLLESON

.LONG TERM...LOOKS RIGHT NOW LIKE NORTHWEST WASHINGTON AND BRITISH
COLUMBIA MAY GET AN ATMOSPHERIC RIVER EVENT OVER THE WEEKEND. MOST OF
THE MOISTURE AND RAINFALL SHOULD MISS US...BUT THE SURFACE HIGH
PRESSURE SYSTEM TO OUR WEST TO SOUTHWEST WILL PUSH SOME OF THE
MOISTURE SOUTHWARD TO THE SOUTHWEST WASHINGTON AND NORTHWEST OREGON
COAST. THIS BRINGS A CHANCE FOR SHOWERS ALONG OUR NORTH COAST
STARTING LATE SATURDAY NIGHT THROUGH TUESDAY.

ELSEWHERE UPPER LEVEL RIDGING OVER THE WEST COAST WILL KEEP WEATHER
FAIRLY BENIGN. CALM WINDS OVER THE WILLAMETTE VALLEY WILL MAKE
CONDITIONS FAVORABLE FOR FOG TO DEVELOP EACH NIGHT...AND THIS FOG
WILL LIFT TO STRATUS DURING THE DAY BUT WILL BE SLOW TO CLEAR. -MCCOY

&&

.AVIATION...WITH HIGH PRES OVER THE REGION...WILL MAINTAIN STATUS
QUO WITH DRY AIR MASS AND VFR CONDITIONS THROUGH THU WITH LIGHT N
TO NE FLOW ALOFT. HOWEVER...WILL SEE AREAS OF FOG AND VERY LOW
STRATUS FORM LATER TONIGHT OVER MUCH OF THE INTERIOR. LOCAL
GUIDANCE INDICATES THAT THE FOG/STRATUS WILL BURN OFF BETWEEN 18Z
AND 20Z ON THU...POSSIBLY A TAD EARLIER DEPENDING ON HOW SOLID THE
COVERAGE WINDS UP BEING OVER THE WILLAMETTE VALLEY.

KPDX AND APPROACHES...VFR TONIGHT AND THU...WITH VARIABLE N WINDS.
STILL SEEMS LIKELY THAT WILL HAVE AREAS OF FOG AND LOW IFR STRATUS
BETWEEN 11Z AND 18Z...WITH TOPS LIKELY AROUND 1000 FT.ROCKEY.

&&

.MARINE...LITTLE CHANGE IN OVERALL FORECAST TRENDS. HIGH PRES WILL
REMAIN OVER THE REGION...WHILE THERMAL LOW PRES HUGS NW CALIFORNIA
AND SW OREGON. THE THERMAL TROUGH WILL SHIFT NORTHWARD THU AND
THE WINDS WILL BECOME MORE OFFSHORE...AND SLIGHTLY STRONGER SOUTH
OF CASCADE HEAD. GUSTS MAY REACH 25 KT SOUTH OF CASCADE HEAD
THU EVENING...MAINLY BEYOND 20 NM. THERE WILL BE LITTLE CHANGE IN
THE PRES PATTERN FRI...EXCEPT FOR SLIGHTLY WEAKER GUSTS.

A FRONT WILL DECAY OVER THE N WATERS THIS WEEKEND...AND WEAKEN
THE SURFACE PRES GRADIENT. A POST-FRONTAL SWELL WILL PUSH SEAS
BACK UP TO 7 OR 8 FT SAT NIGHT INTO SUN. HIGH PRES WILL REBUILD
N OF THE WATERS MON...WITH NORTHERLY GRADIENTS STRENGTHENING.

&&

.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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