Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 251432 AAA
AFDPQR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
631 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.
&&

.UPDATE...PERSISTENT SHOWERS IS RESULTING IN SNOW ACCUMULATING
FASTER OVER THE NORTH OREGON CASCADES THAN PREVIOUSLY THOUGHT. SOME
SNOW REPORTING SITES HAVE MEASURED AROUND 2 INCHES OF NEW SNOW IN
THE LAST HOUR. SATELLITE AND RADAR IMAGERY SHOWS BANDS OF SHOWERS UP
STREAM THAT INDICATE SNOW SHOWERS WILL PERSIST OVER THE NORTHERN
OREGON CASCADES THROUGH THE MORNING...AND POSSIBLY INTO THE
AFTERNOON. IF THE SNOW RATES CONTINUE AT 1 TO 2 INCHES PER
HOUR...SOME LOCATIONS CAN EXPECT TO SEE OVER A HALF OF FOOT OF NEW
SNOW BY THIS AFTERNOON. HAVE THEREFORE ISSUED A WINTER WEATHER
ADVISORY FOR THE NORTHERN OREGON CASCADES FOR ELEVATIONS ABOVE 3500
FEET. THE SNOW WILL NOT BE UNIFORMLY DISTRIBUTED AND SOME AREAS WILL
MEASURE MUCH LESS SNOW THAN OTHERS. HOWEVER...THINK THE PASSES WILL
HAVE QUITE A BIT OF SNOW MAKING TRAVEL OVER THE CASCADES EXTRA
DIFFICULT. TJ

.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...THE COOL AND UNSTABLE AIR MASS BEHIND THE COLD FRONT
REMAINS OVER THE REGION...WITH GENERALLY VFR CONDITIONS
PERSISTING. MODERATE NW FLOW WILL CONTINUE SOME SHOWER ACTIVITY
THIS MORNING...PRIMARILY OVER THE ELEVATED TERRAIN. STILL THINK
SOME SLIGHT STABILIZING WILL OCCUR...RESULTING IN INCREASED MVFR
COVERAGE BETWEEN AROUND 12Z AND 17Z. SOME POTENTIAL FOR IFR
CONDITIONS AT KHIO AND KEUG FROM ABOUT THROUGH 17Z DUE TO SHALLOW
FOG IF SUFFICIENT CLEARING CAN OCCUR. EXPECT IMPROVEMENT TO LOWER
END VFR BY 20Z THU...EXCEPT FOR CONTINUED MVFR OR LOWER OVER THE
OREGON COAST RANGE...WILLAPA HILLS...AND CASCADES. INCREASING CHANCES
FOR MVFR OR LOWER CONDITIONS THU EVENING AND NIGHT...DEPENDING ON
HOW MUCH CLEARING OCCURS TODAY.

KPDX AND APPROACHES...GENERALLY VFR THIS EVENING. MAY SEE BRIEF
MVFR IN SHOWERS THROUGH 12Z. INCREASING MVFR CLOUD DECK WITH
POTENTIAL FOR CIGS AROUND 2000 FT BETWEEN 14Z AND 19Z AS AIR MASS
STABILIZES A BIT. VFR EXPECTED THEREAFTER THROUGH 03Z WITH
INCREASING CHANCES FOR MVFR CIGS INTO THU EVENING AND NIGHT.
CULLEN
&&

.MARINE...HIGH PRESSURE WILL STRENGTHEN OVER THE NE PACIFIC THE
NEXT COUPLE DAYS AND DOMINATE THE WEATHER FOR THE COASTAL WATERS
THROUGH EARLY NEXT WEEK. NW WINDS HAVE EASED A BIT IN THE POST
FRONTAL AIR MASS...THOUGH GUSTS TO 25-30 KT STILL REMAIN THROUGH
THIS MORNING AND CANNOT RULE OUT A FEW LOCAL 35 KT GUSTS IN ANY
STRONGER SHOWERS. OVERALL WIND SPEEDS THEN GRADUALLY DIMINISH
TODAY AND TONIGHT AS THE SURFACE PRESSURE GRADIENT WEAKENS AS AN
AREA OF HIGH PRESSURE IN THE NE PACIFIC BUILDS INTO THE REGION.
MODELS SUGGEST ANOTHER COLD FRONT WILL MOVE DOWN THE BC/WA COAST
THIS WEEKEND FOR ANOTHER PERIOD OF GUSTY ADVISORY LEVEL W-NW WINDS
LATE SAT AND SUN.

SEAS HAVE CONTINUED TO BUILD A LITTLE OVER THE WATERS...WITH BUOY
46029 JUST SHY OF 19 FT AS OF 2 AM. BUOY OBSERVATIONS HAVE TRENDED
A FEW FEET ABOVE GUIDANCE OVER THE PAST SIX HOURS. WHILE STILL
BELIEVE SEAS WILL GRADUALLY EASE THROUGH THE DAY TODAY...THEY MAY
CONTINUING RUNNING ABOVE 10 FT FOR A FEW MORE HOURS THAN GUIDANCE
WOULD INDICATE...AND SEAS MAY NOT DROP BELOW THIS THRESHOLD UNTIL
THIS EVENING. THUS...THE TIMING OF THE ADVISORY FOR HAZARDOUS
SEAS THROUGH 6 PM TODAY LOOKS ON TRACK. SEAS MAY BUILD AGAIN THIS
WEEKEND AS A SMALL DYNAMIC FETCH ASSOCIATED WITH THE FRONTAL
SYSTEM MENTIONED PREVIOUSLY SLIDES DOWN THE PACIFIC COAST FROM THE
NORTH. HOWEVER...SEAS LIKELY FALL TO 6 FT OR LESS FOR MUCH OF NEXT
WEEK IN DEVELOPING OFFSHORE FLOW.   CULLEN
&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
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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