Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 251801 AAA
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
1001 AM PST THU DEC 25 2014

.SYNOPSIS...HIGH PRESSURE OFFSHORE WITH LOW PRESSURE OVER THE
ROCKIES WILL KEEP THE REGION UNDER A COOLER NORTHERLY FLOW THROUGH
THE END OF THE WEEK. AN UPPER JET WILL MAINTAIN RAIN AND MOUNTAIN
SNOW SHOWERS THROUGH TONIGHT. AN UPPER SHORTWAVE TROUGH DROPPING DOWN
THE BC COAST WILL BRING ANOTHER ROUND OF LOW ELEVATION RAIN AND
MOUNTAIN SNOW THIS WEEKEND. COLDER AND DRIER OFFSHORE FLOW IS
EXPECTED SUNDAY NIGHT THROUGH WEDNESDAY.

&&

.MORNING UPDATE...SHOWERS ARE BEGINNING TO TAPE OFF A BIT THIS
MORNING AS THE UPPER JET WEAKENS. SOME NEW SNOW WILL CONTINUE ACROSS
THE NORTH OREGON CASCADES...BUT AMOUNTS WILL BE SOMEWHAT LIMITED
BASED ON STRENGTH OF SHOWERS. WILL RIDE THE WINTER WEATHER ADVISORY
UNTIL SHOWERS DISSIPATE...WHICH SHOULD BE SOMETIME THIS AFTERNOON AS
THE WEAKENED JET DRIFTS EAST. NORTHWEST FLOW IS ALSO FAVORING SHOWERS
IN THE NORTH OREGON COAST RANGE AND WILLAPA HILLS...BUT WITH SNOW
LEVELS AROUND 3000 FT AND RISING SLIGHTLY THROUGH THE DAY...PRECIP
THERE SHOULD REMAIN RAIN. BOWEN

.PREVIOUS SHORT TERM...TODAY THROUGH SUNDAY...AN UPPER RIDGE IS
AMPLIFYING OFFSHORE NEAR THE 135W LONGITUDE TODAY AND FRIDAY. AN
UPPER JET RIDING OVER THE RIDGE WILL MAINTAIN ENOUGH LOW LEVEL
CONVERGENCE/LIFT OVER THE PACIFIC NW TO CONTINUE SHOWERS TODAY AND
TONIGHT DESPITE THE NORMALLY DRYING NORTHERLY WINDS ALOFT. NORTHWEST
WINDS CLOSER TO THE SURFACE WILL ENHANCE OROGRAPHIC PRECIPITATION
AND EXPECT A GREATER FREQUENCY OF SHOWERS FOR THE HIGHER TERRAIN OF
THE COAST RANGE AND CASCADES WITH MAINLY ISOLATED SHOWERS FOR THE
INTERIOR LOWLANDS.

THE SNOW LEVEL WILL REMAIN BELOW THE CASCADE PASSES AND AN ADDITIONAL
1 TO 3 INCHES OF SNOW IS POSSIBLE ABOVE 3000 FEET BY TONIGHT. THE
SNOW ACCUMULATIONS WILL NOT BE UNIFORMLY DISTRIBUTED DUE TO THE
SHOWERY NATURE OF THE PRECIPITATION. THE UPPER JET WILL WEAKEN AND
MOVE INLAND LATE TONIGHT AND THE SHOWERS WILL BECOME LESS
FREQUENT...AND BARELY NOTICEABLE FRIDAY.

A SHORTWAVE UPPER TROUGH WILL SLIDE SOUTH ALONG THE BRITISH COLUMBIA
COAST FRIDAY NIGHT TOWARDS WASHINGTON STATE. RAIN AND MOUNTAIN SNOW
WILL MOVE FROM NORTH TO SOUTH ACROSS WESTERN WASHINGTON AND NORTHWEST
OREGON THIS WEEKEND AS THE SHORTWAVE MOVES OVER EASTERN WASHINGTON
AND OREGON. SNOW LEVELS WILL HOVER AROUND 3000 FEET AND EXPECT 5 TO
12 INCHES OF SNOW FOR THE SW WASHINGTON AND NORTHERN OREGON CASCADES
SATURDAY AND SATURDAY NIGHT. THE LANE COUNTY CASCADES SHOULD SEE 2 TO
5 INCHES OF SNOW ABOVE 3000 FEET SATURDAY. AN ADDITIONAL 1 TO 3
INCHES OF SNOW IS LIKELY FOR THE CASCADES ON SUNDAY. RAINFALL AMOUNTS
FOR THE LOWER ELEVATIONS WILL BE AROUND A HALF OF AN INCH FOR THE
COAST...COAST RANGE...AND THE CASCADE FOOTHILLS...WITH AROUND A
QUARTER OF AN INCH FOR THE WILLAMETTE VALLEY. TJ

LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...HIGH PRESSURE STARTS TO
BUILD OVER THE NORTHEAST PACIFIC SUNDAY...MOVING ONSHORE OVER THE
PACIFIC NORTHWEST ON MONDAY. THIS WILL PUSH SHOWERS OFF TO THE
EAST...BUT BRING NOTICEABLY COLDER AIR INTO THE REGION. COLD EASTERLY
WINDS OUT OF THE GORGE LOOK LIKELY TO DEVELOP MONDAY AND PERSIST
THROUGH WEDNESDAY. HIGH PRESSURE MEANS FOG WILL LIKELY DEVELOP IN
VALLEY LOCATIONS...THOUGH DRY EASTERLIES OUT OF THE GORGE WILL HELP
KEEP THE NORTH WILLAMETTE VALLEY CLEAR. -MCCOY
&&

.AVIATION...A FEW SHOWERS LINGER IN THE MOIST AND SLIGHTLY
UNSTABLE AIR MASS ACROSS SW WASHINGTON AND NW OREGON. HOWEVER
CONDITIONS ARE GENERALLY VFR ASIDE FROM SPOTTY MVFR IN SHOWERS.
EXPECT THIS TO CONTINUE MUCH OF THE DAY...THEN MORE WIDESPREAD
MVFR CIGS ARE EXPECTED TO DEVELOP OVERNIGHT TONIGHT. THERE ARE
ALSO A COUPLE PATCHES OF FOG WHICH HAVE DEVELOPED THIS MORNING...
MAINLY NEAR KHIO...ANY IFR/LIFR SHOULD LIFT OR BREAK UP BY MIDDAY.
MOIST LOW-LEVEL AIR MASS WILL CONTINUE MOUNTAIN OBSCURATIONS ON
THE COAST RANGE AND CASCADES THROUGH THIS EVENING.

KPDX AND APPROACHES...GENERALLY VFR TODAY AND THIS EVENING THROUGH
02Z-04Z...THEN MVFR CIGS DEVELOPING THEREAFTER AND PERSISTING THE
REST OF THE NIGHT. EXPECT A COUPLE BRIEF PERIODS OF MVFR IN -SHRA
TODAY...MAINLY BEFORE 21Z.  WEAGLE

&&

.MARINE...HIGH PRESSURE CONTINUES TO STRENGTHEN OFFSHORE THIS
MORNING...WITH NW FLOW GRADUALLY DECREASING. WINDS STILL GUSTING
TO 23 KT AT BUOY 46029...BUT THERE HAS DEFINITELY BEEN A DOWNWARD
TREND OVER THE PAST FEW HOURS. THEREFORE IT APPEARS THE SCA FOR
WINDS CAN EXPIRE AT 10 AM. SEAS REMAIN 11-13 FT IN RESIDUAL SWELL
FROM THE RECENT BURST OF NW WINDS ACROSS THE WATERS. THESE SEAS
SHOULD GRADUALLY COME DOWN TODAY...FALLING BELOW 10 FT BY THIS
EVENING.

AFTER A LULL TONIGHT AND FRIDAY...IT APPEARS ANOTHER COLD FRONT
WILL PUSH DOWN THE COAST THIS WEEKEND FOR ANOTHER SURGE OF NW
WINDS AND SEAS. THIS SYSTEM MAY PRODUCE A SMALL DYNAMIC FETCH
WHICH COULD CAUSE SEAS TO BUILD ABOVE THE 10-12 FT PRESENTLY
FORECAST FOR A BRIEF PERIOD THIS WEEKEND. STRONG HIGH PRESSURE
WILL THEN DOMINATE THE PACIFIC NORTHWEST AND ADJACENT WATERS EARLY
NEXT WEEK...WITH LIGHT TO MODERATE OFFSHORE FLOW AND SEAS FALLING
TO 6 FT OR LESS FOR MUCH OF NEXT WEEK.WEAGLE

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR
     NORTHERN OREGON CASCADES.

WA...NONE.
PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 10 AM PST THIS MORNING FOR
     COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 PM PST THIS
     EVENING FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE
     OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 11 PM
     PST THIS EVENING.

&&

$$

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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