Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 240506
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
905 PM PST SUN NOV 23 2014

.SYNOPSIS...A BREAK IN THE WEATHER IS EXPECTED THROUGH MONDAY
MORNING. A WARM FRONT WILL REACH THE AREA LATE MONDAY WITH RAIN
DEVELOPING. WET WEATHER IS ON TAP FOR TUESDAY AND POSSIBLY WEDNESDAY
WITH HIGH SNOW LEVELS IN THE MOUNTAINS. ANOTHER WEATHER SYSTEM WILL
DEVELOP OVER THE AREA THURSDAY.

&&

.SHORT TERM...JUST A NARROW CONVERGENCE ZONE PERSISTS AROUND
SNOQUALMIE PASS AT THIS TIME...WITH WSDOT CAMERAS SHOWING SNOW AT
THE PASS RIGHT NOW. THE CONVERGENCE ZONE SHOULD WASH OUT ANY TIME
NOW AS ONSHORE FLOW ENDS OVER THE NEXT FEW HOURS. WITH PREDOMINANTLY
PRECIP-FREE WEATHER FOR THE OVERNIGHT AND MORNING HOURS...WILL BE
SAFE TO LET THE WINTER STORM WARNING IN THE CASCADES EXPIRE AT 10
PM.

A FLAT UPPER RIDGE WILL EXPAND NORTHWARD INTO THE NE PAC AND PAC NW
ON MON AND TUE. STRONG WARM ADVECTION LIFT NEAR THE PERIPHERY OF THE
RIDGE AND WESTERLY FLOW ALOFT WILL PUSH A WELL-DEFINED WARM FRONT
N-NE THROUGH THE FCST AREA LATER MON AND TUE. MOISTURE AND
INCREASING LIFT WILL CAUSE RAIN TO START DEVELOPING OVER WRN WA
AROUND MID-DAY MON...WITH EXPANSION AND INTENSIFICATION OF THE RAIN
ON MON NIGHT AND TUE. SNOW LEVELS WILL RISE SUBSTANTIALLY ON MON NGT
AND TUE...SO ONLY LOOKING FOR A FEW HOURS OF SNOW IN THE MTN PASSES
AT THE ONSET OF PRECIP BEFORE A DECIDED CHANGE TO ALL RAIN ON MON
NGT.

THE EAST-WEST ORIENTED WARM FRONT WILL TURN UP STATIONARY SOMEWHERE
AROUND LATITUDE 48 TO 50 ON TUE. WRN WA WILL THEN BE IN THE WARM
SECTOR SOUTH OF THE FRONT...WITH 850 MB TEMPS RUNNING ARND +5C TO
+7C. ATMOSPHERIC MOISTURE CONTENT WILL BE HIGH...AND STRONG WESTERLY
FLOW ALOFT WILL LEAD TO STRONG OROGRPHIC LIFT OVER THE MTNS. THIS
WILL BRING A FEW INCHES OF RAIN TO THE OLYMPICS AND CASCADES ON TUE
AND TUE NGT...WITH THE AXIS OF HEAVIER RAIN LIFTING NORTH TO NEAR
THE CANADIAN BORDER ON WED.   HANER

.LONG TERM...FROM PREVIOUS DISCUSSION...THE EXTENDED FORECAST INTO
NEXT WEEKEND IS CLOSE TO CLIMO FOR NOW WITH NO ATTEMPT TO SORT OUT
THE DIFFERENCES IN THE MODELS OF LATE. THE GENERAL TREND HAS BEEN TO
MAKE THANKSGIVING WET BUT AFTER THAT THE FCSTS DIVERGE. THE
BAROCLINIC ZONE...THE DIRTY RIDGE WARM FRONT...SHOULD REDEVELOP AND
MERGE WITH A SOUTHERN STREAM SHORTWAVE IN THE CONFLUENCE OF THE
UPPER LEVEL FLOW OVER WA...SO THANKSGIVING COULD BE ANOTHER WET DAY.
BEYOND THAT IT IS DIFFICULT TO SAY WHETHER WRN WA WILL REMAIN WET
AND MILD...OR COOL OFF LIKE THE 12Z ECMWF SOLUTION.

&&

.HYDROLOGY...A HYDROLOGIC OUTLOOK WAS ISSUED FOR RIVERS FLOWING OFF
THE CASCADES FROM WHATCOM SOUTH THROUGH KING COUNTY. HEAVY RAIN WITH
HIGH SNOW LEVELS ARE LIKELY IN THE MOUNTAINS TUESDAY AND TUESDAY
NIGHT. NWRFC FORECASTS SHOW THE RIVERS TO KEEP AN EYE ON ARE THE
NOOKSACK... STILLAGUAMISH... AND SNOQUALMIE. INDEED...THE STRONG
WARM ADVECTION AND WESTERLY FLOW ALOFT USUALLY FAVOR THESE BASINS IN
TERMS OF HEAVIER RAIN AND RIVER RISES.  HANER

&&

.AVIATION...MODERATE NW FLOW ALOFT WILL BECOME WLY ON MON. AT THE
SURFACE...A RIDGE OF HIGH PRES IS OVER THE AREA THIS EVENING. IT
WILL MOVE OFF TO THE NE MON AS A WARM FRONT TO THE SW OF THE AREA
APPROACHES...THEN MOVES INTO THE AREA MON EVENING. THE LOW LEVEL AIR
MASS IS STABLE AND MAINLY DRY THIS EVENING. HIGH LEVEL MOISTURE MON
MORNING WILL THICKEN AND LOWER AS THE WARM FRONT APPROACHES THE
AREA...AND LIGHT RAIN IS EXPECTED TO DEVELOP MON AFTERNOON.

EXPECT MAINLY VFR CONDITIONS TONIGHT. SOME LOCAL IFR IN FOG CAN BE
EXPECTED IN MORE FOG-PRONE RIVER VALLEYS AND IN THE SOUTH INTERIOR.
CIGS WILL LOWER TO AROUND 030 MOST AREAS MON AFTERNOON THEN TO
015-020 MON AFTERNOON AS PRECIPITATION FORMS OVER THE AREA. ALBRECHT

KSEA...EXPECT ONLY SOME SCT-BKN HIGH CLOUDS THROUGH MON MORNING WITH
SE WINDS 4-7 KT. CLOUDS WILL THICKEN AND LOWER MON MORNING AND WILL
FALL TO AROUND 030 MID AFTERNOON. LIGHT RAIN WILL LOWER CIGS TO
AROUND 020 LATE MON AFTERNOON. ALBRECHT

&&

.MARINE...WINDS WILL BECOME LIGHT OVERNIGHT AS A WEAK RIDGE OF HIGH
PRES DEVELOPS OVER THE AREA THEN MOVES NE.

A WARM FRONT WILL APPROACH THE WATERS FROM THE S ON MON. THIS WILL
LEAD TO INCREASING S TO SE WINDS OVER THE WATERS MON AND MON NIGHT.
THE FRONT WILL BECOME STATIONARY OVER THE WATERS OR JUST TO THE
NORTH OF THE WATERS ON TUE AND WED. STRONG SW FLOW ON THE ORDER OF
20 TO 30 KT CAN BE EXPECTED TO THE SOUTH OF THIS FRONT. THE FRONT
WILL SLIP BACK SOUTH ON THU...THEN FRASER OUTFLOW AND STRONG
OFFSHORE FLOW IS POSSIBLE NEXT FRI.

HAZARDOUS SWELL WILL CONTINUE ALONG THE COAST THROUGH MON MORNING
AND THEN SUBSIDE A BIT ON MON AFTN. HANER/ALBRECHT

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER STORM WARNING IN THE CASCADES EXPIRES AT 10 PM.
PZ...SMALL CRAFT ADVISORY COAST AND WEST ENTRANCE TO THE STRAIT.
     SMALL CRAFT ADVISORY EAST ENTRANCE TO THE STRAIT...ADMIRALTY
      INLET AND NORTHERN INLAND WATERS STARTING 7 AM PST MONDAY.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR CONDITIONS.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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




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