Flood Watch 1, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PST MON JAN 2 2012

.SYNOPSIS...A FRONTAL SYSTEM OVER WESTERN WASHINGTON WILL BRING RAIN
AND LOCALLY WINDY CONDITIONS THIS EVENING...THEN MOVE NORTHEAST OF
THE AREA OVERNIGHT. ANOTHER FRONTAL SYSTEM WILL DEVELOP OVER THE
OFFSHORE WATERS TUESDAY AND MOVE INLAND WEDNESDAY THROUGH THURSDAY.
AN UPPER RIDGE WILL BUILD OVER THE REGION LATE THIS WEEK...AND
ANOTHER FRONTAL SYSTEM WILL DEVELOP OFFSHORE THIS WEEKEND.

&&

.SHORT TERM...A PACIFIC FRONTAL SYSTEM IS MOVING INTO WESTERN
WASHINGTON FROM THE SOUTHWEST THIS AFTERNOON. RAIN STARTED OVER THE
SOUTHWEST CORNER OF THE STATE AROUND 10 AM AND HAS BEEN SPREADING
NORTHEAST ACROSS THE FORECAST AREA. SOUTHEAST WINDS ARE ALSO
INCREASING...WITH ESPECIALLY ALONG THE COAST AND IN THE NORTHWEST
INTERIOR. AT 2 PM BELLINGHAM REPORTED SOUTHEAST WIND GUSTING TO 51
MPH. AT 3 PM TEMPERATURES WERE MILD...RANGING FROM THE UPPER 40S TO
THE 50S.

THE FRONTAL SYSTEM WILL MOVE ACROSS THE FORECAST AREA THIS EVENING.
I WILL POST A WIND ADVISORY FOR THE COAST AND NORTHWEST INTERIOR
THIS EVENING. ANOTHER IMPACT OF THIS SYSTEM IS A CHANCE OF LIGHT
FREEZING RAIN IN THE PASSES...WHERE TEMPERATURES ARE BELOW FREEZING
AND EASTERLIES WINDS CONTINUE. ONCE THE FRONT MOVES NORTH OF THE
FORECAST AREA LATE THIS EVENING...THE WINDS WILL EASE AND THE THREAT
OF FREEZING RAIN SHOULD END.

THE LONG WAVE UPPER RIDGE WILL BUILD OVER THE PACIFIC NORTHWEST
LATER TONIGHT AND TUESDAY. AT THE SAME TIME A STRONG MOIST
BAROCLINIC ZONE WILL DEVELOP ALONG THE WEST SIDE OF THE RIDGE...
EXTENDING FROM VANCOUVER ISLAND SOUTH-SOUTHWEST ACROSS THE OFFSHORE
WATERS. ONCE AGAIN THERE WILL BE A STRONG SOUTHEAST SURFACE PRESSURE
GRADIENT ACROSS THE REGION...AND MORE WIND ADVISORY TYPE
SOUTHEASTERLIES ARE LIKELY AT THE COAST AND IN THE NORTHEAST
INTERIOR.

WARM FRONTAL PRECIPITATION WILL FALL OVER MUCH OF THE FORECAST AREA
TUESDAY AND TUESDAY NIGHT...WITH THE HEAVIEST AMOUNTS OVER THE
OLYMPICS AND NORTH COAST AND PERHAPS THE MOUNT BAKER AREA. THE SNOW
LEVEL WILL BE HIGH...BUT EASTERLIES IN THE PASSES WILL MAINTAIN THE
POSSIBILITY OF FREEZING RAIN AT TIMES.

THE BAROCLINIC BAND AND SURFACE COLD FRONT WILL WEAKEN AND MOVE
SLOWLY INLAND WEDNESDAY AND WEDNESDAY NIGHT. IT WILL BRING
PRECIPITATION TO THE ENTIRE FORECAST AREA. AGAIN THE HEAVIEST
AMOUNTS WILL BE OVER THE COAST...OLYMPICS...AND MOUNT BAKER AREA.
THE SNOW LEVEL WILL STILL BE HIGH...GRADUALLY FALLING FROM AROUND
6500 FT TO 5000 FT AS THIS FEATURE MOVES THROUGH. THE UPPER TROUGH
BEHIND THE FRONT WILL ARRIVE THURSDAY FOR A SHOWERY DAY...AND THE
SNOW LEVEL WILL FALL TO AROUND 3000 FT.   MCDONNAL

.LONG TERM...THE MODELS ARE IN REASONABLE AGREEMENT FOR THE EXTENDED
PERIOD FRIDAY THROUGH MONDAY. A WEAK SYSTEM MIGHT JUST BRUSH WESTERN
WASHINGTON FRIDAY AS AN UPPER RIDGE BUILDS OFFSHORE. THE UPPER RIDGE
WILL SHIFT INLAND ON SATURDAY...AND THE PATTERN SEQUENCE SATURDAY
THROUGH MONDAY LOOKS VERY SIMILAR TO THE CURRENT SITUATION. AS THE
UPPER RIDGE MOVES EAST OF THE CASCADES ON SATURDAY...A WEAK WARM
FRONT WILL BRUSH THE AREA. THEN A BAROCLINIC ZONE EXTENDING FROM
VANCOUVER ISLAND SOUTH-SOUTHWEST ACROSS THE OFFSHORE WATERS WILL
MOVE SLOWLY INLAND SUNDAY AND MONDAY. SNOW LEVELS WILL REMAIN FAIRLY
HIGH. THERE COULD BE SOME DRY PERIODS THIS WEEKEND...ESPECIALLY ON
SATURDAY.   MCDONNAL

&&

.HYDROLOGY...THERE IS A CHANCE THAT THE SKOKOMISH RIVER WILL FLOOD
AS A RESULT OF THE RAINFALL THAT OCCURS TUESDAY THROUGH WEDNESDAY
NIGHT. IF FLOODING DOES OCCUR IT WOULD LIKELY BE MINOR. THERE HAS
BEEN SOMEWHAT OF A TREND TOWARD LESS PRECIPITATION IN SUCCESSIVE
MODEL RUNS...AND THE HYDROLOGIC MODEL AT THE NORTHWEST RIVER
FORECAST CENTER KEEPS THE RIVER BELOW FLOOD STAGE.

FLOODING IS UNLIKELY ON ALL OTHER RIVERS IN THE FORECAST AREA FOR
THE NEXT 7 DAYS.   MCDONNAL

&&

.AVIATION...A FRONT WILL MOVE INLAND THIS EVENING IN WESTERLY FLOW
ALOFT. AT THE SURFACE STRONG SOUTHEAST WINDS WILL TAPER OVERNIGHT.
AIR MASS IS MOIST AND STABLE. RAIN WILL LAST INTO THE EVENING THEN
TURN MORE SHOWERY BY MIDNIGHT.

CEILINGS ARE STILL RUNNING AROUND 5K FT AT INLAND TERMINALS BUT WILL
FALL THIS EVENING TO THE MVFR CATEGORY. LOCAL CEILINGS AROUND 1K FT
ARE POSSIBLE AS THE FRONT MOVES THROUGH THE PUGET SOUND AREA AROUND
04Z. SOME VISIBILITY RESTRICTIONS OF 2SM IN RAIN ARE POSSIBLE. SOME
IMPROVEMENT IS LIKELY LATE TONIGHT BUT CEILINGS ARE LIKELY TO REMAIN
IN THE 3-5K FT RANGE THROUGH TUESDAY.

KSEA...DISCUSSION ABOVE APPLIES. WINDS WILL BE SOUTHEAST 8-12 KT
EARLY THIS EVENING...RISING TO 10G20 KT FOR A FEW HOURS LATER THIS
EVENING AS THE FRONT PASSES...THEN BACK TO SOUTHEAST 5-8 KT TUESDAY.
CHB

&&

.MARINE...FRONT STALLED OFF THE COAST THIS MORNING. NOW THAT IT IS
COMING ASHORE...IT HAS GAINED STRENGTH AND GALE WARNINGS ARE UP FOR
ALL WATERS EXCEPT CENTRAL STRAIT AND PUGET SOUND. THESE GALES SHOULD
LAST SEVERAL HOURS...THEN WINDS WILL TAPER OVERNIGHT. THERE WILL BE
A BRIEF SURGE OF WESTERLIES...15-25 KT...DOWN THE STRAIT. THEN WINDS
TURN BACK TO EASTERLY THERE AND SOUTHEASTERLY ELSEWHERE.

GALES WILL RESUME TUESDAY ON THE COAST AND TUESDAY AFTERNOON INLAND
AS THE NEXT SYSTEM APPROACHES. THIS WINDY PERIOD IS LIKELY TO LAST
INTO WEDNESDAY BEFORE WINDS FINALLY TAPER THURSDAY. AN OFFSHORE
RIDGE THAT MOVES SLOWLY INLAND SHOULD KEEP WINDS LIGHT FRIDAY AND
SATURDAY. CHB

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY IN EFFECT UNTIL 10 PM PST THIS EVENING FOR THE
       CENTRAL AND NORTH WASHINGTON COAST AND NORTHWEST INTERIOR.
PZ...GALE WARNING ALL WATERS EXCEPT CENTRAL STRAIT AND PUGET
        SOUND.
    .SMALL CRAFT ADVISORY CENTRAL STRAIT AND PUGET SOUND.
    .SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

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