Gale Warning 24, NWS Seattle, WA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
320 AM PDT SAT MAR 28 2009

.SYNOPSIS...A VIGOROUS FRONTAL SYSTEM WILL MOVE ACROSS WESTERN
WASHINGTON TODAY WITH RAIN IN THE LOWLANDS AND SNOW IN THE
MOUNTAINS. SHOWERS WILL DECREASE ON SUNDAY AS THE SYSTEM MOVES EAST
AND AN UPPER LEVEL RIDGE MOVES OVER THE AREA. COOL AND UNSETTLED
WEATHER WILL PREVAIL NEXT WEEK AS A STRONG JETSTREAM ACROSS THE
NORTHEAST PACIFIC DRIVES MORE WEATHER SYSTEMS ACROSS THE REGION.

&&

.SHORT TERM...A STRONG JET STREAM OF 160 KTS OR MORE WEST OF 140W
WILL HELP AN UPPER LEVEL TROUGH AND ASSOCIATED FRONT RAPIDLY
STRENGTHEN AS THEY APPROACH WESTERN WASHINGTON LATER TODAY AND
TONIGHT. RECENT MODEL RUNS BRING THE SURFACE LOW ONSHORE NEAR OR
JUST SOUTH OF HOQUIAM THIS AFTERNOON. A FRONT WILL PUSH THROUGH
INTERIOR WESTERN WASHINGTON LATE THIS AFTERNOON. A GOOD WESTERLY
PUSH NEAR AND BEHIND THE FRONT COMBINED WITH DECENT MOISTURE WILL
SQUEEZE OUT UPWARDS OF 12 TO 20 INCHES OF SNOW IN THE CASCADES
BETWEEN NOW AND THIS TIME TOMORROW...ESPECIALLY FROM THE STEVENS
PASS AREA SOUTHWARD. LESSER AMOUNTS ARE EXPECTED OVER THE NORTH
CASCADES AND OLYMPICS. WILL PROBABLY LEAVE THE CURRENT WINTER STORM
WARNING AS IS FOR THE SAKE OF CONTINUITY...AND INCOMING SHIFT CAN
DECIDE ON NECESSARY ADJUSTMENTS OR CHANGES IN COVERAGE.

OTHER ITEM OF CONSIDERATION IS THE POSSIBILITY OF A LITTLE LOWLAND
SNOW. BASED ON RECENT EVENTS...ITS BEST NOT TO OVERLOOK THIS
POSSIBILITY DESPITE THE FACT THAT ITS NEARLY APRIL. THE SCENARIO
LOOKS MARGINAL...BUT THE TRACK OF THE SURFACE LOW AND SUB 1300 METER
1000/850 THICKNESSES SUGGEST A LIGHT DUSTING IS POSSIBLE OVER THE
HOOD CANAL AREA AND SOUTH KITSAP PENINSULA TODAY...AND PERHAPS
WITHIN THE PUGET SOUND CONVERGENCE ZONE THIS EVENING. IN EITHER
CASE...I EXPECT TO WORD THE FORECAST AS UP TO AN INCH POSSIBLE.

WEAK UPPER LEVEL RIDGING BUILDS INTO THE REGION ON SUNDAY FOR A
SHORT-LIVED GENERALLY DRY PERIOD FROM MIDDAY SUNDAY INTO EARLY
MONDAY. A LITTLE SUN ON SUNDAY AFTERNOON COULD BOOST TEMPS INTO THE
LOWER 50S...STILL BELOW NORMAL. THE NEXT SYSTEM AIDED BY A
PERSISTENT STRONG JET OVER THE NORTHEAST PACIFIC ARRIVES BY MONDAY
AFTERNOON. THIS SYSTEM SHOULD BE MILDER THAN TODAYS...BUT WET
NONETHELESS.

.LONG TERM...NO CHANGES WERE MADE TO THE EXTENDED PORTION OF THE
FORECAST. IT IS SAFE TO SAY THE UNSETTLED PATTERN WILL CONTINUE AS
ADDITIONAL SYSTEMS RIDE UP AND OVER MEAN RIDGE NEAR 140W...ARRIVING
IN WESTERN WASHINGTON EVERY 36 TO 48 HOURS OR SO. 27

&&

.AVIATION...NORTHWEST FLOW ALOFT OVER THE FORECAST AREA WILL BACK TO
SOUTHWEST THIS MORNING AS A PACIFIC FRONTAL SYSTEM AND ITS UPPER
TROUGH APPROACH THE REGION. THE COLD FRONT WILL CROSS WESTERN
WASHINGTON THIS AFTERNOON...FOLLOWED BY THE UPPER TROUGH THIS
EVENING. THE TROUGH WILL HEAD EAST OF THE CASCADES LATER TONIGHT
WITH THE FLOW ALOFT BECOMING NORTHWEST AGAIN.

THE PUGET SOUND CONVERGENCE ZONE THAT FORMED FRIDAY AFTERNOON IS
CLINGING TO LIFE OVER SNOHOMISH COUNTY. IT WILL REMAIN NORTH OF
SEATTLE AND DISSIPATE THIS MORNING. THE INCOMING FRONT WILL SPREAD
PRECIPITATION ACROSS WESTERN WASHINGTON TO THE CASCADES EARLY THIS
MORNING. CONDITIONS WILL DETERIORATE QUICKLY TO MVFR WITH OCCASIONAL
IFR VISIBILITY AND CEILINGS. THE HEAVIEST PRECIPITATION AND WORST
CONDITIONS WILL LIKELY OCCUR LATE THIS MORNING THROUGH LATE
AFTERNOON. A PUGET SOUND CONVERGENCE ZONE WILL PROBABLY DEVELOP LATE
THIS AFTERNOON JUST BEHIND THE COLD FRONT...BUT THERE WILL BE
GENERAL IMPROVEMENT IN CONDITIONS TONIGHT.

KSEA...SOUTH WIND 6-12 KT...BECOMING SOUTHWEST 12-18 KT AND GUSTY
MID AFTERNOON. THE WINDS WILL LIKELY SHIFT TO NORTHWEST LATE
AFTERNOON OR THIS EVENING. THE AIR MASS WILL BE QUITE COOL BEHIND
THE FRONT. SHOWER ACTIVITY WILL BE DECREASING TONIGHT...BUT ANY
SHOWERS THAT DO OCCUR COULD PRODUCE WET SNOW AT KSEA OVERNIGHT.
MCDONNAL

&&

.MARINE...A PACIFIC FRONTAL SYSTEM WILL DEVELOP OVER THE OFFSHORE
WATERS EARLY THIS MORNING...WITH THE VIGOROUS COLD FRONT AND A WEAK
SURFACE LOW MOVING QUICKLY ACROSS THE FORECAST AREA TODAY. MODELS
HAVE ARE HAVING A DIFFICULT TIME PINNING DOWN THE LOCATION AND DEPTH
OF THE SURFACE LOW...BUT IT WILL NOT BE THE BIG WIND PRODUCER WITH
THIS SYSTEM. RATHER THE MAIN EVENT WILL BE THE STRONG NORTHWEST FLOW
THAT DEVELOPS IN THE WAKE OF THE COLD FRONT. THE UW WRF-GFS SHOWS
GALE FORCE WINDS THIS EVENING OVER THE COASTAL AND NORTHERN INLAND
WATERS...AND THERE IS A GOOD CHANCE OF GALES OVER THE CENTRAL STRAIT
OF JUAN DE FUCA...EAST ENTRANCE TO THE STRAIT...AND ADMIRALTY INLET
AS WELL. A GALE WARNING IS NOW IN AFFECT FOR THOSE MARINE ZONES.

IN ADDITION WESTERLY SWELLS WILL BE 12 TO 14 FT OVER THE COASTAL
WATERS THROUGH SUNDAY...BIG ENOUGH FOR HAZARDOUS SEAS BUT PROBABLY
REMAINING JUST BELOW THE CRITERIA FOR A HIGH SURF ADVISORY. THE
POSSIBILITY OF BIG WAVES BEING GENERATED BY NORTHWEST GALES OVER
GEORGIA STRAIT AND THE NORTHERN INLAND WATERS IS ANOTHER MINOR
CONCERN...AS THIS CAN OCCASIONALLY PRODUCE COASTAL FLOODING AT SANDY
POINT NEAR BELLINGHAM. AT THIS TIME IT DOES NOT LOOK LIKE THE PROPER
COINCIDENCE OF HIGH TIDE AND LOW PRESSURE WILL BE THERE FOR THIS TO
OCCUR.

WINDS WILL EASE SUNDAY AS A SURFACE RIDGE MOVES INTO THE OFFSHORE
WATERS. ANOTHER PACIFIC FRONT WILL APPROACH THE REGION MONDAY AND
MOVE THROUGH THE FORECAST AREA MONDAY NIGHT AND TUESDAY. MCDONNAL

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WINTER STORM WARNING CASCADES AND OLYMPICS TODAY THROUGH
     SUNDAY MORNING.
    .AVALANCHE WATCH CASCADES AND OLYMPICS TODAY THROUGH SUNDAY
     MORNING.
PZ...GALE WARNING LATE THIS AFTERNOON THROUGH TONIGHT FOR THE
     COASTAL WATERS...CENTRAL STRAIT OF JUAN DE FUCA...EAST ENTRANCE
     ...ADMIRALTY INLET...NORTHERN INLAND WATERS.
    .SMALL CRAFT ADVISORY THROUGH TONIGHT FOR THE WEST ENTRANCE
     STRAIT OF JUAN DE FUCA.
    .SMALL CRAFT ADVISORY TONIGHT FOR PUGET SOUND AND HOOD CANAL.
    .SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS THROUGH TONIGHT
     FOR GRAYS HARBOR.

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