Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 280529
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
929 PM PST SAT DEC 27 2014

.SYNOPSIS...A COLD FRONT HAD MOVED THROUGH SOUTHWEST WASHINGTON
EARLIER THIS EVENING...AND WILL FINISH MOVING THROUGH NORTHWEST
OREGON BY MIDNIGHT. BRISK ONSHORE FLOW WILL CONTINUE BEHIND THE FRONT
TONIGHT AND SUNDAY AND PRODUCE MORE SHOWERS OVER THE AREA...
ESPECIALLY OVER THE HIGHER TERRAIN...THEN INCREASE SUNDAY NIGHT INTO
MONDAY NIGHT WITH EVEN MORE SHOWERS AS A SECONDARY COLD DISTURBANCE
MOVES THROUGH FROM THE NORTH. LOOK FOR OCCASIONAL SNOW TO CONTINUE IN
THE CASCADES AND ACROSS THE PASSES INTO MONDAY. COLDER HIGH PRESSURE
WILL THEN BUILD INTO THE COLUMBIA BASIN AND CAUSE COLD EAST WINDS TO
DEVELOP ACROSS THE AREA MONDAY AFTERNOON AND INCREASE MONDAY NIGHT
AND TUESDAY FOR DRY CONDITIONS BUT WITH VERY COLD TEMPERATURES AND
ASSOCIATED COLD WIND CHILLS. THE DRY COLD AND BLUSTERY PATTERN WILL
CONTINUE MUCH OF THE COMING WEEK...WITH THE NEXT CHANCE FOR SOME
PRECIPITATION LATE IN THE WEEK AND NEXT WEEKEND...WITH A POSSIBILITY
OF WINTER WEATHER AT LOW ELEVATIONS.
&&

.SHORT TERM...TONIGHT THROUGH TUESDAY...A FAIRLY STRONG COLD FRONT
MOVED THROUGH SOUTHWEST WASHINGTON AND MOST OF NORTHWEST OREGON THIS
EVENING...WITH VERY GOOD PRECIPITATION AMOUNTS IN THE MOUNTAINS...
DECENT AMOUNTS AT THE COAST...AND LESSER AMOUNTS IN THE VALLEYS. THE
STEADIER RAIN IS MOSTLY OVER THOUGH THE FRONT DOES LINGER A BIT IN
EASTERN LANE COUNTY BUT SHOULD MOVE OUT BY MIDNIGHT. THE MODELS SHOW
A PRETTY STEADY STREAM OF ONSHORE FLOW AND SHOWERS COMING IN FROM THE
WEST NORTHWEST OVERNIGHT WHICH SHOULD KEEP THE SNOW GOING THE
CASCADES. WE MAY SEE SOME RAIN SHADOWING IN THE VALLEYS THOUGH.

THE ONSHORE FLOW CONTINUES SUNDAY BUT MAY NOT BE QUITE AS STRONG AS
TONIGHT...THEN PICKS UP SUNDAY NIGHT INTO MONDAY AS A TRAILING
SECONDARY COLD DISTURBANCE DROPS DOWN FROM THE NORTH SUNDAY NIGHT AND
MONDAY MORNING. THIS SHOULD GIVE US AN INCREASE IN THE SHOWERS AND
SNOW IN THE CASCADES. WITH HOLIDAY TRAVEL EXPECTED SUNDAY AND
POSSIBLY MONDAY...HAVE DECIDED TO CONTINUE THE SNOW ADVISORIES IN THE
CASCADES INTO MONDAY.

WE MAY SEE SOME ACCUMULATING SNOW IN THE CASCADE FOOTHILLS AND HIGHER
COAST RANGE SUNDAY NIGHT INTO MONDAY AS WELL...AS SNOW LEVELS DROP TO
AROUND 2000 FEET BY SUNDAY EVENING AND TO NEAR OR BELOW 1000 FEET BY
MONDAY MORNING. AMOUNTS COULD GET CLOSE TO ADVISORY THRESHOLDS.

AFTER THAT...DRY WEATHER WILL DEVELOP AS COLD HIGH PRESSURE WILL
SPREAD DOWN INTO THE COLUMBIA BASIN AND CAUSE COLD EAST WINDS TO
DEVELOP THROUGH THE COLUMBIA RIVER GORGE AND UP AND OVER THE CASCADES
AND ACROSS THE REMAINDER OF SOUTHWEST WASHINGTON AND NORTHWEST
OREGON. THE WINDS WILL DEVELOP BY MONDAY AFTERNOON...AND INCREASE
MONDAY NIGHT AND TUESDAY AND BE QUITE STRONG...POSSIBLY ENOUGH FOR
SOME AREAS OF TREE DAMAGE AND POWER OUTAGES. THE EAST WINDS WILL
USHER IN THE COLDEST AIR MASS OF THE SEASON SO FAR...AND IN
COMBINATION WITH THE WIND WILL PRODUCE SOME COLD WIND CHILLS. AN
SPECIAL WEATHER STATEMENT HAS BEEN ISSUED DISCUSSING ALL OF THIS.
TOLLESON

.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...COLD...DRY WEATHER
CONTINUES THROUGH THE DAY WEDNESDAY...AS HIGH PRESSURE SITS OVER THE
AREA. ECMWF AND GFS ARE STARTING TO KEY IN ON A LOW PRESSURE SYSTEM
THAT WILL DIVE DOWN THE COAST LATE THIS WEEK...SHIFTING WINDS BACK TO
THE NORTHWEST AND BRINGING PRECIPITATION. THERE IS STILL CONSIDERABLE
UNCERTAINTY ON THE TIMING OF THIS SYSTEM...THOUGH. IF THIS PANS OUT
AS FORECAST RIGHT NOW...A CHANCE OF WINTRY MIX ALL THE WAY TO THE
FLOOR OF THE WILLAMETTE VALLEY IS POSSIBLE INITIALLY THURSDAY NIGHT
INTO EARLY FRIDAY. AS THE FRONT MOVES THROUGH TEMPERATURES ARE STILL
BELOW FREEZING...UNTIL ONSHORE WINDS AND DAYTIME HEATING CAN BRING
TEMPERATURES BACK ABOVE FREEZING LATE FRIDAY MORNING OR AFTERNOON. IF
THE FRONT IS SLOWER THAN FORECAST AND MOVES THROUGH DURING THE DAY ON
FRIDAY...TEMPERATURES WILL MORE LIKELY BE ABOVE FREEZING KEEPING IT
ALL RAIN. RAIN LOOKS TO CONTINUE INTO SATURDAY. -MCCOY
&&

.AVIATION...A COLD FRONT WILL CONTINUE TO MOVE THROUGH THE THE AREA
THIS EVENING BRINGING MVFR CONDITIONS TO AREAS NEAR THE FRONT. IN THE
WAKE OF THE FRONT...THE STEADY RAIN WILL BECOME MORE SHOWERY AND
CONDITIONS WILL GENERALLY IMPROVE TO VFR FOR THE OVERNIGHT HOURS AS
COOLER AND MORE UNSTABLE AIR MOVES IN. THERE MAY BE SOME MVFR OR EVEN
IFR CONDITIONS IN SOME SHELTERED AREAS WHERE FOG MAY FORM. THE
MID-LEVEL C0LD AIR ADVECTION WEAKENS AFTER DAYBREAK SUNDAY...SO THERE
IS A CHANCE AN EXTENDED CLEAR PERIOD COULD ALLOW IFR TO LIFR FOG TO
FORM...PARTICULARLY AT KEUG. A WEAK LOW PRESSURE WILL DROP SOUTHWARD
ACROSS THE AREA SUNDAY EVENING. AS THIS SYSTEM
APPROACHES...CONDITIONS COULD DETERIORATE INTO THE MVFR CATEGORY
AFTER 4PM SUNDAY.

KPDX AND APPROACHES...MAINLY VFR CONDITIONS THIS EVENING AND
OVERNIGHT AS MID LEVEL COLD ADVECTION DESTABILIZES THE LOWER
ATMOSPHERE IN THE WAKE OF THE FRONTAL PASSAGE. AN OCCASIONAL MVFR CIG
WILL BE POSSIBLE...BUT THESE SHOULD BE SHORT LIVED. ADDITIONAL FLIGHT
RESTRICTIONS COULD CREEP INTO THE TERMINAL TOWARDS 4PM SUNDAY
AFTERNOON AS A WEAK LOW PRESSURE DROPS SOUTHWARD WEST OF THE
CASCADES.
&&

.MARINE...A FRONT WILL DROP SOUTHWARD ACROSS THE WATERS THIS
EVENING...BRINGING GUSTY NORTHWEST WINDS AND HIGH SEAS TO THE WATERS.
WINDS AND SEAS SHOULD BE HIGHEST ACROSS THE NORTHERN COASTAL WATERS
WITH SOLID SMALL CRAFT ADVISORY WINDS WITH GUSTS OF 25 TO 30 KT. SEAS
SHOULD GENERALLY TOP OUT IN THE 11 TO 13 FT RANGE TOWARDS THE CENTRAL
AND NORTH OREGON COAST. EXPECT SEAS TO START SUBSIDING SUNDAY
AFTERNOON AND SUNDAY NIGHT...LIKELY DROPPING BELOW 10 FT MONDAY
MORNING.

A WEAK LOW PRESSURE MAY DEVELOP AND DRIFT SOUTHWARD ACROSS THE INNER
WATERS LATE SUNDAY NIGHT OR MONDAY MORNING...BUT IMPACTS TO MARINE
INTERESTS WILL BE FAIRLY MINIMAL. AS THE LOW PRESSURE DROPS SOUTH OF
THE AREA...OFFSHORE PRESSURE GRADIENTS WILL STRENGTHEN RAPIDLY. THIS
WILL ALLOW GUSTY EAST TO NORTHEAST WINDS TO DEVELOP ACROSS THE WATERS
FOR THE SECOND HALF OF MONDAY...LASTING THROUGH AT LEAST THE MIDDLE
PART OF NEXT WEEK. WITH NO MAJOR WESTERLY SWELLS...SEA CONDITIONS
WILL PRIMARILY BE DOMINATED BY WIND WAVES DURING THE PEAK OF THE EAST
WINDS, WHICH WILL LIKELY OCCUR MONDAY NIGHT INTO TUESDAY. TW/CN
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY UNTIL NOON PST MONDAY FOR CASCADES IN
     LANE COUNTY-NORTHERN OREGON CASCADES.

WA...WINTER WEATHER ADVISORY UNTIL 7 AM PST MONDAY FOR SOUTH
     WASHINGTON CASCADES.

PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 10 PM PST SUNDAY FOR
     COASTAL WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR OUT
     60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 9 AM PST MONDAY
     FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR OUT
     60 NM.

     SMALL CRAFT ADVISORY FOR WINDS UNTIL 6 PM PST SUNDAY FOR COASTAL
     WATERS FROM CASCADE HEAD OR TO FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR UNTIL 1 PM PST
     SUNDAY.

&&

$$

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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