Funnel Cloud in Washington, December 18, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
310 PM PST TUE DEC 18 2012

.SYNOPSIS...A STRONG FRONTAL SYSTEM WILL BRING RAIN AND WIND AS WELL
AS HEAVY MOUNTAIN SNOW ON WEDNESDAY. COOL UNSETTLED CONDITIONS WILL
PERSIST THURSDAY AND FRIDAY WITH AN UPPER TROUGH. GRADUAL DRYING
WILL OCCUR NEXT WEEKEND AND EARLY NEXT WEEK AS THE TROUGH MOVES OUT
OF THE AREA AND HIGH PRESSURE BUILDS IN FROM THE WEST.

&&

.SHORT TERM...A VIGOROUS FRONTAL SYSTEM WILL MOVE THROUGH THE AREA
LATER TONIGHT THROUGH WEDNESDAY NIGHT. THIS SYSTEM WILL BRING
ANOTHER BATCH OF WEATHER ISSUES.

LOWLAND SNOW...THE AIR MASS IS CURRENTLY COLD FOR SNOW DOWN TO NEAR
SEA LEVEL. THE INITIAL WARM FRONTAL RAIN EARLY WEDNESDAY MORNING
WILL LIKELY START OUT AS SNOW FOR MOST LOWLAND SPOTS. THIS IS A
TRICKY FORECAST. WARMER AIR WILL MOVE IN PRETTY QUICKLY WITH SNOW
CHANGING TO RAIN. MOST AREAS SHOULD SEE AN INCH OR LESS OF
ACCUMULATION BUT MORE IS POSSIBLE IF THE COLD AIR TAKES LONGER TO
SCOUR. THE EXCEPTION IS THE HOOD CANAL AREA WHERE EASTERLY LOW LEVEL
FLOW WILL LIKELY TRAP COLD AIR FOR A FEW HOURS LONGER...ALLOWING FOR
AT LEAST A FEW INCHES OF ACCUMULATION BEFORE SNOW CHANGES TO RAIN
LATER IN THE MORNING. A WINTER WEATHER ADVISORY HAS BEEN ISSUED TO
COVER THE EXPECTED SNOW OVER THE HOOD CANAL AREA WEDNESDAY MORNING.

WINDS...MARGINAL HIGH WINDS ARE POSSIBLE COAST AND NORTH INTERIOR
LATE TONIGHT AND WEDNESDAY...FIRST WITH THE WARM FRONT WEDNESDAY
MORNING THEN WITH THE COLD FRONT LATER IN THE DAY. THE HIGH WIND
WATCH HAS BEEN UPGRADED TO A HIGH WIND WARNING FOR THE COAST AND
NORTH INTERIOR FROM LATE TONIGHT THROUGH WEDNESDAY AFTERNOON.

MOUNTAIN SNOW...THERE WILL BE SIGNIFICANT SNOW IN THE MOUNTAINS
WEDNESDAY AND WEDNESDAY NIGHT. SOUTHWEST FLOW ALOFT WEDNESDAY WILL
BECOME MORE SOUTHERLY WEDNESDAY NIGHT. THIS SUPPORTS HEAVIEST
AMOUNTS OVER THE VOLCANOES...UP TO 2 FEET BY THURSDAY MORNING. THE
PASSES AND HURRICANE RIDGE SHOULD SEE LESSER AMOUNTS WITH THIS FLOW
PATTERN...MAYBE A FOOT. THE WINTER STORM WATCH HAS BEEN UPGRADED TO
A WARNING THE MOUNTAINS.

AN UPPER TROUGH WILL DIG OVER THE EASTERN PACIFIC WITH MOIST
SOUTHWEST FLOW ALOFT ON THURSDAY. WITH THE TROUGH DIGGING
OFFSHORE...THE FRONT WILL BE SLOW TO CLEAR THE AREA WITH RAIN
GRADUALLY CHANGING TO SHOWERS. SNOW SHOULD CONTINUE OVER THE
MOUNTAINS IN THIS PATTERN...ESPECIALLY THE VOLCANOES. THIS GENERAL
PATTERN WILL CONTINUE INTO FRIDAY WITH A SHORT WAVE PERHAPS
ENHANCING THE SHOWERS DURING THE DAY ALTHOUGH MODELS DIFFER WITH THE
DETAILS ON THIS. SCHNEIDER

.LONG TERM...A BROAD UPPER TROUGH WILL REMAIN OVER THE EASTERN
PACIFIC NEXT WEEKEND. THE MAIN STORM TRACK WILL BE AIMED WELL SOUTH
OF THE AREA WITH JUST DISORGANIZED SHOWERS OVER WESTERN WASHINGTON.
THERE SHOULD BE A DRYING TREND SUNDAY AS THE UPPER TROUGH SAGS
FURTHER SOUTH AND EAST.

THE MODELS BEING TO SHOW SIGNIFICANT DIFFERENCES STARTING AROUND
MONDAY. THE GFS HAS A DRY RIDGE BUILDING OVER THE AREA MONDAY AND
CONTINUING INTO TUESDAY. THE ECMWF BRINGS A FAIRLY WET FRONTAL
SYSTEM ONSHORE MONDAY NIGHT AND TUESDAY. THE CURRENT FORECAST IS A
BLEND OF THESE TWO...BASICALLY CLIMO POPS. SCHNEIDER

&&

.HYDROLOGY...FLOODING IS NOT EXPECTED ON AREA RIVERS THROUGH THE
NEXT 7 DAYS. SCHNEIDER

&&

.AVIATION...THE UPPER LEVEL TROUGH OVER E WA WILL CONTINUE E TONIGHT
WITH SHOWERS OVER W WA ENDING BY 04Z. AREAS OF MVFR CIGS THROUGH THE
INTERIOR HAVE HUNG ON...SO SHOULD CONTINUE THROUGH THIS EVENING.

A STRONG WARM FRONT WILL APPROACH THE WA COAST TONIGHT WITH
INCREASING S FLOW AT LOW LEVELS AND STRONG GUSTY WINDS DEVELOPING
ALONG THE COAST AND N INTERIOR AREAS. RAIN WILL SPREAD INLAND AFTER
08Z WITH CIGS LOWERING TO MVFR. PERIODS OF LIGHT SNOW OR RAIN/SNOW
MIXED ARE POSSIBLE OVER THE INTERIOR 11Z-17Z WITH IFR CIGS/VIS
PROBABLE. THE WARM FRONT WILL REACH THE WA COAST AROUND 12Z THEN
MOVE INLAND. A STRONG TRAILING COLD FRONT WILL REACH THE COAST
AROUND 00Z-02Z.

KSEA...THE BKN010-015 LAYER HAS BEEN RESISTANT TODAY SO I WILL KEEP
IT GOING INTO THIS EVENING. THERE WILL PROBABLY BE A BRIEF PERIOD
WHERE IT LIFTS TO BKN020-030 LATER THIS EVENING AND BEFORE THE WARM
FRONT PRECIP ARRIVES. WINDS WILL REMAIN S-SW 8-15 KT THROUGH 06Z.

AN APPROACHING WARM FRONT WILL SPREAD PRECIP OVER THE AREA TONIGHT
STARTING AROUND 10Z. EVAPORATIVE COOLING AT LOW LEVELS...OR THE
WET-BULB EFFECT...WILL LIKELY CHANGE THE RAIN TO SNOW AROUND
12Z...WITH SNOW LASTING THROUGH ABOUT 15Z. LOW LEVEL WARM ADVECTION
FROM SOUTH WINDS AFTER THAT SHOULD CHANGE THE PRECIP BACK TO RAIN OR
BRIEFLY A RAIN OR SNOW MIX AFTER 15Z. SNOW ACCUMULATIONS AT KSEA MAY
END UP BEING AN INCH OR LESS. ALSO QUITE POSSIBLE IS THAT THE LOW
LEVEL WARM ADVECTION WILL DEVELOP SOONER...MEANING THAT THE PRECIP
REMAINS RAIN OR AT WORST A RAIN-SNOW MIX. CIGS WILL REMAIN BELOW
2000 FEET WITH VISIBILITY DROPPING TO 3SM OR LESS IN SNOW.

STRONG S-SW WINDS ALOFT 45-65 KT FROM FL050-FL100 WILL LAST FROM 12Z
WEDNESDAY THROUGH 06Z THURSDAY. KAM

&&

.MARINE...A STRONG WARM FRONT WILL APPROACH THE WA COAST
TONIGHT...REACHING THE COAST AROUND 12Z. STRONG S-SE PRESSURE
GRADIENTS WILL RAISE GALES OVER THE COASTAL AND NORTH INLAND WATERS
AFTER 06Z. GALES WILL LIKELY CONTINUE THROUGH 03Z WITH THE APPROACH
OF THE TRAILING COLD FRONT. THE COLD FRONT SHOULD REACH THE COAST
WEDNESDAY EVENING 00Z-02Z. WINDS WILL DIMINISH WEDNESDAY NIGHT
BEHIND THE COLD FRONT...BUT MAY REMAIN AT SCA LEVELS.

A GALE WARNING WAS ISSUED FOR THE CENTRAL STRAIT ALTHOUGH ONLY THE
EASTERN CORNER NEAR DUNGENESS SPIT AND ADJACENT TO THE WINDIER EAST
ENTRANCE WILL EXPERIENCE GALES.

A LARGE LOW WILL SETTLE IN ABOUT 500 NM OFFSHORE AROUND 45N/135W
LATE WEDNESDAY NIGHT AND CONTINUE THROUGH ABOUT SATURDAY. WINDS
SHOULD BE GENERALLY SUB SCA LEVEL...BUT IT LOOKS LIKE THERE MAY BE
ONE SHORTWAVE MOVING ACROSS THE AREA FRIDAY WHICH MAY PRODUCE SCA
WINDS. KAM

&&

.AVALANCHE...FOLLOWING A STRONG WEATHER SYSTEM THAT DEPOSITED HEAVY
AMOUNTS OF WIND DRIVEN SNOW OVER A VARIETY OF WEAK LAYERS SUNDAY
THRU EARLY TUESDAY AND PRODUCED A GENERALLY HIGH AVALANCHE DANGER
ABOVE 4 TO 5000 FEET...A BRIEF BREAK MID-LATE TUESDAY SHOULD ALLOW A
SLIGHT RESPITE AND A BRIEF AND SLIGHT DECREASE IN THE AVALANCHE
DANGER. HOWEVER...ANOTHER STRONG FRONTAL SYSTEM MOVING INTO THE
REGION LATE TUESDAY NIGHT AND WEDNESDAY SHOULD PRODUCE FURTHER HEAVY
SNOWFALL AND STRONG WINDS AND FUEL ANOTHER ROUND OF GENERALLY
ELEVATED AVALANCHE DANGERS AND A REISSUE OF AVALANCHE WARNING
CONDITIONS. INSTEAD OF BC TRAVEL...PERHAPS SAFER TIMES CAN BE HAD
SHOPPING FOR BEACONS...PROBES...AND SHOVELS...AND THINKING ABOUT
AVALANCHE DANGER. PLEASE VISIT WWW.NWAC.US FOR FURTHER DETAILS.
MOORE

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER STORM WARNING NORTH AND CENTRAL CASCADES WEDNESDAY
     MORNING THROUGH THURSDAY MORNING.
    .HIGH WIND WARNING NORTH AND CENTRAL COAST 10 PM TONIGHT THROUGH
     WEDNESDAY.
    .WINTER WEATHER ADVISORY HOOD CANAL AREA MIDNIGHT TO 10 AM
     WEDNESDAY.
PZ...GALE WARNING COAST...STRAIT OF JUAN DE FUCA...ADMIRALTY INLET...
     NORTHERN INLAND WATERS LATE TONIGHT AND WEDNESDAY.
    .SMALL CRAFT ADVISORY COAST AND WEST ENTRANCE FOR HAZARDOUS SEAS
     THIS EVENING.
    .SMALL CRAFT ADVISORY PUGET SOUND.
    .SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

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