Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 261832 AAA
AFDSEW

AREA FORECAST DISCUSSION...UPDATED ADDED AVN MAR SECTIONS
NATIONAL WEATHER SERVICE SEATTLE WA
1032 AM PST WED NOV 26 2014

.SYNOPSIS...A WARM FRONT WILL REMAIN NEAR THE CANADIAN BORDER TODAY.
A COLD FRONT WILL MOVE EAST ACROSS THE AREA TONIGHT FOR MORE RAIN
AND WINDY CONDITIONS. RAIN WILL CONTINUE ON THANKSGIVING DAY AS
ANOTHER COLD FRONT APPROACHES FROM THE NORTH THEN CROSSES THE AREA
ON FRIDAY. A COLD UPPER LEVEL TROUGH WILL BE OVER THE AREA FRIDAY
NIGHT AND SATURDAY FOR A CHANCE OF SHOWERS...POSSIBLY MIXED WITH
SNOW. COOL DRY AND BREEZY WEATHER WILL DEVELOP SATURDAY NIGHT AND
SUNDAY AS HIGH PRESSURE BUILDS OVER BRITISH COLUMBIA.

&&

.SHORT TERM...WESTERN WASHINGTON IS IN THE WARM SECTOR OF A WARM
FRONT THAT IS NEARLY STATIONARY OVER SOUTHERN B.C. THIS MORNING.
TEMPERATURES WERE RATHER MILD OVERNIGHT FROM THE GREATER PUGET SOUND
REGION SOUTHWARD...AND REMAIN SO THIS MORNING WITH READINGS IN THE
MID TO UPPER 50S. THE WARM AIR HAS NOT QUITE REACHED THE NW INTERIOR
WHERE TEMPS WERE STILL IN THE UPPER 40S...BUT SHOULD GET THERE
EVENTUALLY TODAY. THE LULL IN RAIN WILL CONTINUE UNTIL THE NEXT
FRONT ARRIVES TONIGHT.

THE APPROACHING FRONT WAS OFFSHORE NEARING 130W AT 16Z/8 AM THIS
MORNING AND IS EXPECTED TO CROSS THE COAST AROUND 06Z/10 PM TONIGHT.
FROPA OVER THE INTERIOR SHOULD BE BEFORE 12Z/4 AM. S-SE SURFACE
WINDS WILL INCREASE AHEAD OF THE FRONT LATE THIS AFTERNOON AND
EVENING. STRONGEST WINDS SHOULD PEAK THIS EVENING IN THE LOW END
WIND ADVISORY RANGE FOR THE USUAL AREAS...COAST AND N INTERIOR.
WINDS WILL DIMINISH AFTER MIDNIGHT AS THE FRONT MOVES INLAND.

IN ADDITION...STRONG SW LOW LEVEL FLOW ALOFT AT 850 MB IS EXPECTED
TO DEVELOP AS THE FRONT APPROACHES THIS EVENING THEN CONTINUE IN THE
35-45KT RANGE THROUGH THURSDAY NIGHT AS A COLD FRONT OVER B.C. MOVES
S. THE SW FLOW WILL IMPACT MAINLY THE OLYMPICS AND N CASCADES WITH
HEAVY RAIN...WITH WIDESPREAD 3 INCH AMOUNTS AND A BULLSEYE OF AROUND
5 INCHES AROUND MT BAKER FOR THE 36 HOUR PERIOD 00Z THURSDAY THROUGH
12Z FRIDAY. SNOW LEVELS WILL REMAIN HIGH...6000 TO 7000 FEET TONIGHT
LOWERING TO 5000-6000 FEET THURSDAY NIGHT. THE HEAVY RAIN HAS A GOOD
CHANCE OF PRODUCING SOME FLOODING ON SOME OF THE RIVERS FLOWING OFF
THE N CASCADES. A FLOOD WATCH REMAINS IN EFFECT...SEE THE HYDRO
SECTION BELOW FOR MORE DETAILS.

AFTER TONIGHTS FRONT EXITS THE AREA EARLY THURSDAY MORNING...THE OLD
WARM FRONT OVER SOUTHERN B.C. WILL BE DRIVEN SOUTH ACROSS W WA AS A
COLD FRONT...BY A STRONG UPPER LEVEL TROUGH DIVING SOUTH FROM
NORTHERN B.C.  MODELS BRING THE BACK EDGE OF THE FRONT TO THE N
INTERIOR FRIDAY MORNING...THEN DOWN ACROSS PUGET SOUND LATE FRIDAY
AFTERNOON...THEN FINALLY APPROACHING THE OREGON BORDER LATE FRIDAY
EVENING. RAIN WILL CONTINUE WITH THE FRONT AS IT MOVES S.

INTERESTING WEATHER WILL CONTINUE FRIDAY NIGHT. THE LOW LEVEL AIR
MASS WILL REMAIN MOIST. THE APPROACHING UPPER LEVEL TROUGH IS VERY
COLD ALOFT AND WILL GRADUALLY COOL THE AIR MASS ENOUGH OVERNIGHT SO
THAT RAIN AND SNOW MIXED OR JUST SNOW IS POSSIBLE BY LATE FRIDAY
NIGHT INTO SATURDAY MORNING. THE UPPER LEVEL TROUGH WILL PROVIDE
SOME LOW LEVEL INSTABILITY AND LIFT TO SUPPORT SHOWER ACTIVITY. IN
ADDITION WINDS WILL BE RIGHT FOR A CONVERGENCE ZONE TO FORM OVER
CENTRAL PUGET SOUND.

A STRONG SURFACE HIGH FORMING OVER THE B.C.INTERIOR WILL GENERATE
FRASER RIVER VALLEY OUTFLOW WINDS ON SATURDAY. THIS WILL SPREAD COOL
DRY LOW LEVEL AIR SOUTHWARD ACROSS W WA...WITH CLEARING FROM THE
NORTH SATURDAY AFTERNOON AND EVENING. THE NE WINDS COULD BE STRONG
ENOUGH TO REACH WIND ADVISORY CRITERIA OVER THE FAR N INTERIOR. THE
COLD AIR WILL LEAD TO LOWS IN THE 20S ACROSS W WA SUNDAY MORNING. KAM

.LONG TERM...PREVIOUS DISCUSSION FROM THE 330 AM AFD...LONG RANGE
MODELS SHOW A COOL AND DRY AIR MASS OVER WESTERN WA ON SUNDAY. HIGH
PRES OVER INTERIOR B.C. WILL MAINTAIN EASTERLY FLOW THROUGH THE
PASSES. LOWS SUNDAY MORNING WILL BE DOWN TO THE 20S TO LOWER 30S
ONCE AGAIN. HIGHS ARE ALSO BELOW NORMAL ON SUNDAY WITH UPPER 30S TO
LOWER 40S EXPECTED. MODELS WERE SHOWING SOME MOISTURE SPREADING
NORTH SUN NIGHT OR MON BUT THEY ARE NOW BACKING OFF ON THIS IDEA. SO
THE FORECAST IS NOW LOOKING DRIER OVER THIS PERIOD AS WELL. THE
FORECAST IS ALSO LOOKING DRIER THROUGH MIDWEEK NOW AS THE EURO TRIES
TO BUILD A RIDGE OVER THE PAC NW. 33

&&

.HYDROLOGY...A WARM FRONT LIFTED NORTH INTO SOUTHERN BRITISH
COLUMBIA THIS MORNING WHERE THE HEAVIER RAIN NOW RESIDES. THE
COASTAL RADAR IS PICKING UP SOME STEADY LIGHT RAIN CONCENTRATED
ALONG THE COAST AND W/SW SLOPES OF THE OLYMPICS. UP TO A COUPLE
TENTHS HAS FALLEN THE PAST 3 HOURS OVER THE OLYMPICS WITH THE
RAINFALL RATES CONTINUING A DOWNTREND. RAIN IS ALSO DECREASING
ACROSS THE N CASCADES WHERE UP TO 1 INCH FELL OVERNIGHT. RAIN IS NOW
IN A LULL ACROSS WRN WA AND ANY ADDITIONAL RAIN AMOUNTS SHOULD BE
LESS THAN A HALF INCH AND MOSTLY CONFINED TO THE CASCADES OF
WHATCOM/SKAGIT COUNTIES AND THE OLYMPICS. BECAUSE RAINFALL HAS
TAPERED...THE ODDS OF THE NOOKSACK AT CEDARVILLE REACHING FLOOD
TODAY ARE LOW BUT STILL NEEDS TO BE WATCHED. THE STILLAGUAMISH
REACHED FLOOD OVERNIGHT BUT IS ON THE DOWNTURN AND SHOULD FALL BELOW
FLOOD LATER TODAY.

THE SNOQUALMIE RIVER AT THE FALLS CRESTED EARLY THIS MORNING WITH
THE CREST MOVING DOWNSTREAM THROUGH CARNATION LATE THIS AFTERNOON.
FLOODING ON THE SNOQUALMIE WILL CONTINUE THROUGH TONIGHT. THE
SKYKOMISH RIVER RAN WITHIN A FOOT OF FLOOD STAGE EARLIER THIS
MORNING BUT IS NOW ON THE DOWNTURN. THE SNOHOMISH...WHICH IS FORMED
BY THE CONFLUENCE OF THE SKYKOMISH AND SNOQUALMIE RIVERS...COULD
HAVE SOME FLOODING LATER TODAY.

THE RIVERS THAT FLOW OFF MOUNT RAINIER ARE RECEDING. THE FLOODING
HAS ENDED FOR THE CARBON AND NISQUALLY RIVERS...BUT FLOODING WILL
CONTINUE FOR THE COWLITZ AND REACH OF THE PUYALLUP NEAR ORTING.

ANOTHER FRONT WILL BRING RENEWED RAINFALL TO WRN WA TONIGHT AND
THURSDAY...LOCALLY HEAVY IN THE MOUNTAINS. THE OLYMPICS AND NORTH
CASCADES WILL RECEIVE THE HEAVIEST RAINFALL...BUT LOCALLY UP TO 5
INCHES OVER MOUNT RAINIER AND SKYKOMISH-SNOQUALMIE-TOLT-SNOHOMISH
BASIN IS POSSIBLE TOO. THE SNOW LEVEL WILL BE 5500 TO 7000 FT FOR
MOST OF THE EVENT...THEN FALL ON FRIDAY AS A COLD FRONT MOVES
THROUGH FROM THE NORTHWEST AND PRECIPITATION DECREASES.

A MAJOR FLOODING EPISODE IS UNLIKELY...BUT THE RAINFALL COULD
CERTAINLY RENEW FLOODING ON THE RIVERS THAT FLOODED OR ALMOST
FLOODED AND SOME OTHER RIVERS COULD REACH FLOOD STAGE AS WELL. A
FLOOD WATCH REMAINS IN EFFECT THROUGH FRIDAY...WHICH INCLUDES ALL
THE COUNTIES WITH RIVERS FLOWING OFF THE WEST SLOPES OF THE CASCADES
AND MASON COUNTY FOR THE POSSIBILITY OF A FLOOD ON THE SKOKOMISH.

COLDER AND DRIER WEATHER IS LIKELY THIS WEEKEND...SO RIVERS SHOULD
RECEDE AND THE FLOOD THREAT WILL END FOR THE FORESEEABLE FUTURE.

MERCER

&&

.AVIATION...THE FLOW ALOFT IS STRONG AND FROM THE WEST. THE AIR MASS
IS RATHER MOIST AFTER THE PASSAGE OF A WARM FRONT. CIGS ARE MVFR TO
VFR ACROSS THE AREA TODAY AS THE LAST OF THE SHOWERS MOVE OUT. A
COLD FRONT IS TIMED TO MOVE THROUGH THE AREA OVERNIGHT
TONIGHT...CIGS WILL BE HIGHER JUST BEFORE FRONTAL PASSAGE AND THEN
FALL JUST AFTER FRONTAL PASSAGE TO LOW MVFR IN MOST AREAS. SLY
SURFACE WINDS WILL BE STRONG AND GUSTY WITH THE FRONT AND INTO THE
MORNING.

KSEA...SOUTH WIND INCREASING FROM 10 TO 12 KT TODAY TO 12 TO 14 KT
OVERNIGHT WITH GUSTS TO 20 KT DURING AND AFTER FRONTAL PASSAGE
AROUND 7 OR 8Z. CONDITIONS WILL DETERIORATE LATE TONIGHT AS THE NEXT
FRONTAL SYSTEM ARRIVES. JSMITH

&&

.MARINE...A COLD FRONT WILL APPROACH THE WATERS TODAY AND MOVE
ONSHORE TONIGHT. SMALL CRAFT ADVISORY SOUTHERLY WINDS WILL BE
COMMON IN MOST WATERS TODAY...THEN GALES FOR SOME WATERS TONIGHT AS
THE FRONT MOVES THROUGH. MODERATE TO STRONG ONSHORE FLOW WILL
PREVAIL BEHIND THE FRONT ON THURSDAY.

ANOTHER COLD FRONT WILL MOVE THROUGH THE WATERS EARLY 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. JSMITH

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...FLOOD WATCHES AND WARNINGS IN EFFECT FOR PORTIONS OF
     WESTERN WASHINGTON.
PZ...SMALL CRAFT ADVISORY ALL WATERS.
    .SMALL CRAFT ADVISORY GRAYS HARBOR BAR FOR ROUGH BAR.
    .GALE WARNING COASTAL WATERS...ENTRANCES STRAIT OF JUAN DE
     FUCA...AND NORTHERN INLAND WATERS LATE THIS AFTERNOON AND
     TONIGHT.

&&

$$

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