Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 260014
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
414 PM PST TUE NOV 25 2014

.SYNOPSIS...A WARM FRONT WILL REMAIN NEAR THE CANADIAN BORDER
TONIGHT AND WEDNESDAY WITH RAIN AT TIMES OVER THE NORTH PART AND
RAIN LIKELY ELSEWHERE TONIGHT. RAIN WILL DIMINISH WITH JUST A CHANCE
OF RAIN ON WEDNESDAY. A FRONT WILL MOVE ACROSS THE AREA WEDNESDAY
NIGHT FOR MORE RAIN AND WINDY CONDITIONS. RAIN WILL CONTINUE ON
THANKSGIVING DAY AS ANOTHER COLD FRONT APPROACHES FROM THE NORTH
THEN CROSSES THE AREA THURSDAY NIGHT. COOL DRY AND BREEZY WEATHER
WILL DEVELOP BY FRIDAY AFTERNOON AND CONTINUE THROUGH THE WEEKEND AS
HIGH PRESSURE BUILDS OVER BRITISH COLUMBIA. WEAK WEATHER SYSTEMS MAY
BRING A LITTLE RAIN EARLY NEXT WEEK.

&&

.SHORT TERM...THE WARM FRONT OVER W WA LOOKS LIKE IT HAS FINALLY
MOVED UP NEAR THE CANADIAN BORDER THIS AFTERNOON. RADAR SHOWS RAIN
IS CONCENTRATED UP OVER WHATCOM COUNTY AND THE N CASCADES. HOWEVER W
FLOW IS STILL BRINGING SOME OROGRAPHIC RAIN TO THE REST OF THE W
SLOPES OF THE CASCADES. THE WARM FRONT IS EXPECTED TO REMAIN NEAR
THE BORDER TONIGHT BRINGING RAIN TO THE FAR NORTHERN LOWLANDS AND
MODERATE TO LOCALLY HEAVY RAIN TO THE N CASCADES. A LITTLE LIGHT
RAIN IS LIKELY OVER THE REST OF THE W WA LOWLANDS TONIGHT WITH
BREEZY S WINDS.

WEDNESDAY STILL LOOKS LIKE A LULL DAY WITH A WEAKER WARM FRONT STILL
UP OVER SOUTHERN B.C. AND THE NEXT FRONT STILL OFFSHORE. IR IMAGERY
SHOWS THIS OFFSHORE FRONT ALONG 140W NEAR THE MAIN LOW NEAR
40N/148W. MODELS REMAIN CONSISTENT IN BRINGING THIS FRONT ACROSS W
WA WEDNESDAY NIGHT. BESIDES ANOTHER INCREASE IN RAIN...THE STRONG SW
LOW LEVEL FLOW AHEAD OF AND BEHIND THE FRONT WILL BRING ANOTHER
ROUND OF HEAVY RAIN TO THE OLYMPICS AND N CASCADES. 3-5 INCHES OF
RAIN IS POSSIBLE OVER THESE AREAS FROM WEDNESDAY NIGHT THROUGH
THURSDAY EVENING...OR 00Z THURSDAY THROUGH 06Z FRIDAY. THIS MEANS
RAIN AT TIMES AND WINDY CONDITIONS OVER THE LOWLANDS FOR
THANKSGIVING DAY...AND POTENTIALLY MORE RIVER FLOODING FOR N
CASCADES RIVERS AND POSSIBLY SOME OLYMPIC RIVERS.

THE OLD WARM FRONT OVER SOUTHERN B.C. WILL MOVE BACK SOUTH AS A COLD
FRONT THURSDAY NIGHT...BEING PUSHED ALONG BY SHORTWAVE TROUGH
EMBEDDED IN N FLOW ALOFT OVER AK AND NORTHERN B.C.  THE UPPER LEVEL
TROUGH WILL PUSH THE COLD FRONT FROM N TO S ACROSS W WA ON
FRIDAY...WITH RAIN ENDING AND CLEARING FROM THE N. COLD NE FRASER
RIVER OUTFLOW WILL DEVELOP BEHIND THE COLD FRONT FRIDAY AFTERNOON
AND NIGHT BRINGING A COLD DRY AIR MASS AND BREEZY WINDS TO W WA.
FRIDAY NIGHT LOWS WILL DROP INTO THE 30S. KAM

.LONG TERM...BASED ON AGREEMENT BETWEEN THE 12Z GFS AND 12Z ECMWF
SATURDAY AND SUNDAY WERE CLEARED OUT AND THE MENTION OF RAIN
DROPPED...EXCEPT FOR THE S PART LATE SUNDAY. WITH COOL DRY N FLOW
ALOFT OVER THE AREA AND COLD DRY NE FLOW FROM THE FRASER
VALLEY...SKIES WILL BE MOSTLY SUNNY...TEMPERATURES COOL...AND N-NE
WINDS BREEZY. LOWS WILL DROP INTO THE 20S SATURDAY NIGHT WITH HIGHS
SATURDAY AND SUNDAY IN THE UPPER 30S TO MID 40S.
HOWEVER...CONFIDENCE IN THE MODELS IS STILL RATHER LOW...AND THE 18Z
GFS HAS JUST REVERSED COURSE AND BRINGS RAIN UP FROM OREGON ON
SUNDAY. THE ECMWF HAS BEEN MORE CONSISTENT SO REMAINS THE PREFERRED
SOLUTION. THE ECMWF BRINGS MOISTURE AND RAIN NORTHWARD FROM OREGON
SUNDAY NIGHT.  WITH COLD AIR IN PLACE OVER W WA THERE MAY BE A
CHANCE OF SOME LIGHT SNOW...PARTICULARLY OVER THE NORTHERN ZONES AS
THE PRECIP MOVES NORTH. SO FAR THIS IS NOT ACCOUNTED FOR IN THE
FORECASTS AND WILL HAVE TO BE RE-EVALUATED ONCE MODEL CONSISTENCY
AND AGREEMENT IMPROVES. KAM

&&

.HYDROLOGY...HEAVY RAIN OVER THE CENTRAL CASCADES WILL RESULT IN
FLOODING ON SEVERAL RIVERS. IN PARTICULAR THE PUYALLUP AT ORTING HAS
REACHED MAJOR FLOOD STAGE. WITH THE WARM FRONT SHIFTING NORTH TO
NEAR CANADIAN BORDER TONIGHT RAIN OVER THE CENTRAL CASCADES HAS
DIMINISHED.

THE WARM FRONT WILL BRING 1 TO 1.5 INCHES OF RAIN TO THE N CASCADES
TONIGHT BEFORE WEAKENING A BIT MORE AND SHIFTING A LITTLE FARTHER
NORTH OVER SOUTHERN B.C.  WEDNESDAY WILL BE A LULL DAY WITH RAIN
CONTINUING OVER THE N CASCADES...BUT NOT HEAVY. SNOW LEVELS WILL
REMAIN HIGH...6000-7000 FEET TONIGHT AND WEDNESDAY.

A FRONT APPROACHING FROM THE WEST WILL BRING MORE HEAVY RAIN
WEDNESDAY NIGHT THROUGH THURSDAY EVENING. STRONG SW LOW LEVEL
FLOW...45-55 KT...WILL IMPACT THE OLYMPICS AND N CASCADES FROM
SNOQUALMIE PASS NORTHWARD. 3-5 INCHES OF RAIN IS POSSIBLE DURING
THIS PERIOD WHICH MAY DRIVE SOME OF THE NORTHERN CASCADES RIVERS TO
FLOOD STAGE ON THURSDAY...INCLUDING THE NOOKSACK...SKAGIT...
STILLAGUAMISH AND SNOQUALMIE/SNOHOMISH BASINS. A FLOOD WATCH WILL
REMAIN IN EFFECT FOR THIS. RIVERS FLOWING OFF THE OLYMPICS MAY ALSO
REACH FLOOD STAGE...MOST NOTABLY THE SKOKOMISH AND POSSIBLY THE
BOGACHIEL. SNOW LEVELS WILL BE A LITTLE LOWER...IN THE 5500 TO 6500
FOOT RANGE.

THE RAIN WILL END LATE THURSDAY NIGHT AND FRIDAY AS A COLD FRONT
SWEEPS SOUTH ACROSS THE AREA. KAM

&&

.AVIATION...MODERATE WESTERLY FLOW ALOFT AS A FRONT OVER THE CENTRAL
PUGET SOUND AREA THIS AFTERNOON SLOWLY MOVES NORTH INTO BRITISH
COLUMBIA TONIGHT. IFR CEILINGS AND VISIBILITIES HAVE BEEN STUBBORN
TO IMPROVE NORTH OF THE FRONT TODAY...BUT AFTER THE FRONT PASSES
CEILINGS SHOULD LIFT TO LOW END MVFR AT LEAST...1-2K FT...AND
VISIBILITIES WILL IMPROVE TO 4-6SM BR. LIGHT WINDS AT THE SURFACE
WILL INCREASE TONIGHT BEHIND THE FRONT.

KSEA...CONDITIONS SHOULD IMPROVE FROM THE CURRENT IFR TO LOW END
MVFR AROUND 00Z AS THE SURFACE FRONT MOVES NORTH PAST THE TERMINAL.
LIGHT WINDS WILL BECOME SOUTHERLY 10-14KT BEHIND THE FRONT ABOUT
00Z. CHB

&&

.MARINE...A FRONT OVER CENTRAL PUGET SOUND THIS AFTERNOON WILL MOVE
NORTH INTO SOUTHERN BRITISH COLUMBIA TONIGHT. SMALL CRAFT ADVISORY
STRENGTH WINDS WILL SPREAD NORTH BEHIND THE FRONT.

WINDS WILL INCREASE WEDNESDAY AS A COLD FRONT APPROACHES THE COAST.
AT LEAST SMALL CRAFT ADVISORY LEVEL WINDS ARE LIKELY OVER MOST
WATERS WITH GALES POSSIBLE ON THE COAST AND OVER EXPOSED INLAND
AREAS WEDNESDAY NIGHT. A GALE WATCH IS IN EFFECT FOR THE COAST...THE
STRAIT ENTRANCES...AND THE NORTHERN INLAND WATERS WEDNESDAY NIGHT.

ANOTHER COLD FRONT WILL MOVE THROUGH THE WATERS ON FRIDAY. THIS
FRONT WILL BE FOLLOWED BY STRONG FRASER OUTFLOW IN THE NORTHERN
INLAND WATERS AND MODERATE NORTHERLY WINDS OVER THE OTHER WATERS
LATER FRIDAY INTO SATURDAY. CHB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCH IN EFFECT FOR PORTIONS OF THE AREA.
PZ...SMALL CRAFT ADVISORY ALL WATERS EXCEPT EAST ENTRANCE.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.
     GALE WATCH COAST...ENTRANCES...AND NORTHERN INLAND WATERS
     WEDNESDAY NIGHT.

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML











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