Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 262245
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
245 PM PST FRI DEC 26 2014

.SYNOPSIS...MOUNTAIN SHOWERS WILL DECREASE TODAY AS HIGH PRESSURE
BUILDS OVER THE REGION. AN UPPER SHORTWAVE TROUGH DROPPING DOWN
THE BC COAST WILL BRING ANOTHER ROUND OF LOW ELEVATION RAIN AND
MODERATE TO HEAVY MOUNTAIN SNOW THIS WEEKEND. A SECONDARY WAVE WILL
MAINTAIN MOUNTAIN SNOW SHOWERS SUNDAY NIGHT AND MONDAY. COLDER AND
DRIER WEATHER WITH OFFSHORE WINDS IS EXPECTED MONDAY NIGHT THROUGH AT
LEAST WEDNESDAY.

&&

.SHORT TERM...TODAY THROUGH MONDAY...A FEW SHOWERS ARE LINGERING THIS
AFTERNOON MOSTLY IN THE SOUTH WASHINGTON CASCADES AND FOOTHILLS. AS
LOW LEVEL FLOW DECREASES THROUGH THE REST OF TODAY AND AN UPPER JET
MOVES EAST AND OUT OF THE LOCAL VICINITY...SHOWERS WILL MOSTLY COME
TO AN END. QUITE A BIT OF CLOUD COVER REMAINS OVER THE TERRAIN AND
COAST BUT PARTS OF THE INLAND VALLEY ARE FINALLY BEGINNING TO CLEAR A
BIT THIS AFTERNOON. THIS TREND WILL CONTINUE WITH FOG DEVELOPMENT
POSSIBLE AGAIN IN THE VALLEY TONIGHT.

WATER VAPOR IMAGERY SHOWS AN UPPER LEVEL SHORTWAVE TROUGH BEGINNING
TO TREK SOUTH ALONG THE BRITISH COLUMBIA COAST. AS THIS TROUGH
CONTINUES ITS APPROACH TO THE PACIFIC NORTHWEST...PRECIPITATION
CHANCES WILL INCREASE FOR SW WASHINGTON EARLY SATURDAY MORNING...AND
FOR NW OREGON SATURDAY AFTERNOON. NORTHWEST FLOW WILL RESULT IN
OROGRAPHIC ENHANCEMENT AND THE HIGHER TERRAIN WILL RECEIVE MOST OF
THE PRECIPITATION. SNOW LEVELS WILL REMAIN AROUND 3000 FT AND SO
PRECIP WILL FALL ALMOST EXCLUSIVELY AS SNOW IN THE CASCADES. THE
SOUTH WASHINGTON CASCADES WILL BE FAVORED AS PRECIP SPREADS IN FROM
THE NORTH...BUT OREGON CASCADES SHOULD SEE SOME AS WELL. ISSUED A
WINTER WEATHER ADVISORY FOR WA AND OR CASCADES AND ALTHOUGH ADVISORY
LOOKS MARGINAL RIGHT NOW FOR THE OREGON CASCADES...IMPACT COULD BE
HIGH WITH POTENTIAL POST-HOLIDAY WEEKEND TRAVEL. SHOWERS WILL PERSIST
THROUGH SUNDAY AFTERNOON AND THEN ANOTHER SHORTWAVE MOVING OVER THE
INTERIOR SUNDAY NIGHT WILL LIKELY EXTEND LIGHT SHOWERS THROUGH MONDAY
AFTERNOON...BUT BULK OF PRECIP WILL BE SATURDAY AND SATURDAY NIGHT.


STRONG HIGH PRESSURE ALOFT WILL PUSH INLAND OVER THE PACIFIC NW
MONDAY AFTERNOON AS THE TWO SHORTWAVES DIG SOUTH AND EVENTUALLY
FORM AN UPPER LOW OVER SE CA/SW AZ. THIS WILL SET UP A COOLER AND
DRIER WEATHER PATTERN FOR NW OREGON AND SW WASHINGTON FOR NEXT WEEK
WITH PERSISTENT OFFSHORE WINDS. BOWEN/TJ

LONG TERM...MONDAY NIGHT THROUGH THURSDAY NIGHT...A PERSISTENT
WEATHER PATTERN WILL SET UP EARLY NEXT WEEK AS A REX BLOCK DEVELOPS
WITH STRONG HIGH PRESSURE ALOFT OVER THE PACIFIC NW AND AN UPPER LOW
OVER THE CA/AZ. TEMPERATURES ARE EXPECTED TO DRAMATICALLY DROP MONDAY
NIGHT WITH LOWS AROUND 30 FOR THE COAST...LOW TO MID 20S FOR THE
INTERIOR VALLEYS...AND BELOW 20 FOR THE CASCADES AND CASCADE
FOOTHILLS. DAYTIME HIGHS BEGINNING TUESDAY WILL REMAIN NEAR OR BELOW
FREEZING FOR MANY LOCATIONS...WITH THE EXCEPTION OF THE COAST BEING
SLIGHTLY WARMER.  THESE COLD TEMPERATURES ALONG WITH NORTHEAST WINDS
WILL PERSIST THROUGH WEDNESDAY. THE MODELS ARE SHOWING THE BLOCKING
PATTERN DISINTEGRATING THU...ENDING THE OFFSHORE WINDS AND
ALLOWING TEMPERATURES TO RECOVER A LITTLE BIT BY FRIDAY. MODELS TEND
TO BREAK DOWN THESE BLOCKS TOO EARLY AND THERE IS A CHANCE THAT THE
VERY COLD CONDITIONS WILL PERSIST A DAY OR TWO LONGER. BOWEN/TJ

&&

.AVIATION... COASTAL SITES VFR WHILE INLAND SITE HAVE PRIMARILY
MVFR CIGS ACROSS THE AREA DUE TO A STRATUS DECK AROUND FL015 TO
FL025. THIS LOW LEVEL STRATUS WILL LIKELY REMAIN IN PLACE
OVERNIGHT...WITH PATCHY FOG DEVELOPING AFTER 07Z TONIGHT DROPPING
CIGS TO LOW MVFR/IFR. COASTAL SITES TO REMAIN VFR THROUGH THIS
AFTERNOON AND EVENING. RAIN FORECAST TO MOVE IN ALONG THE COAST
WILL DROP CIGS TO MVFR AFTER 03Z...WITH IFR CIGS AND VIS
DEVELOPING AROUND 06-08Z. CIGS TO REMAIN PRIMARILY MVFR THROUGH
THE DAY SATURDAY ACROSS THE AREA...WITH OCCASIONAL REDUCTIONS IN
VIS WITH HEAVIER SHOWERS AND PATCHY FOG INLAND.


KPDX AND APPROACHES...MVFR CIGS TO CONTINUE THROUGH THIS
EVENING. CIGS AND VIS WILL LIKELY DROP TO LOW MVFR/IFR AFTER 04Z
WITH PATCHY FOG OVERNIGHT AND LIGHT RAIN EARLY SATURDAY. CIGS TO
REMAIN PRIMARILY MVFR AGAIN SATURDAY...WITH HEAVIER SHOWERS
CAUSING REDUCTIONS IN VIS.
-MCCOY

&&

.MARINE...HIGH PRESSURE OVER NORTHEAST PACIFIC GIVING WAY FOR A
RELATIVELY WEAK COLD FRONT ON SATURDAY. WINDS INCREASE OUT OF THE
NORTHWEST TO 2O TO 25 KTS WITH GUSTS TO 30 KTS IN THE NORTHERN
WATERS...15 TO 20 KTS WITH FREQUENT GUSTS TO 25 KTS BEHIND THE
FRONT SATURDAY AFTERNOON. THIS WILL HELP TO BUILD SEAS INTO THE
MIDDLE TEENS IN THE NORTHERN WATERS...AND TO LOW TEENS IN THE
SOUTHERN WATERS. SOMEWHAT OF A DYNAMIC FETCH WITH THIS SYSTEM WILL
HELP TO ELEVATE SEAS...DUE TO THE POSITIONING OF THIS LOW PRESSURE
SYSTEM. WINDS START TO DECREASE SUNDAY AFTERNOON. CONTINUED SWELL
OUT OF THE NORTHWEST AT 10 TO 12 FT WILL KEEP SEAS UP ABOVE 10 FT
THROUGH SUNDAY...ONLY STARTING TO SUBSIDE MONDAY MORNING.

MODELS ARE IN GOOD AGREEMENT ON TRANSITION TO OFF-SHORE WINDS ON
MONDAY. THESE WILL PERSIST WITH HIGH PRESSURE OVER THE PACIFIC NW
THROUGH MIDWEEK...WHICH WILL KEEP WINDS AND SEAS FAIRLY BENIGN FOR
THIS TIME OF YEAR THROUGH THIS PERIOD.
-MCCOY

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...WINTER WEATHER ADVISORY FROM 10 AM SATURDAY TO 10 AM PST SUNDAY
     FOR CASCADES IN LANE COUNTY-NORTHERN OREGON CASCADES.

WA...WINTER WEATHER ADVISORY FROM 4 AM SATURDAY TO 4 AM PST SUNDAY
     FOR SOUTH WASHINGTON CASCADES.

PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 10 AM SATURDAY TO 3 PM PST
     SUNDAY FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO FLORENCE OR
     OUT 60 NM.

     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 10 AM SATURDAY TO 9

     AM PST MONDAY FOR COASTAL WATERS FROM CAPE SHOALWATER WA TO
     FLORENCE OR OUT 60 NM.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 6 PM TO
     10 PM PST THIS EVENING.

     SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR FROM 7 AM TO
     11 AM PST SATURDAY.

&&

$$

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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