Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 301037
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
340 AM PDT MON MAR 30 2015

.SYNOPSIS...WARM AIR ADVECTION WILL KEEP RAIN AT TIMES OVER THE
COAST AND NORTHERN INTERIOR TODAY. A COLD FRONT WILL SPREAD RAIN
ACROSS THE AREA TONIGHT FOLLOWED BY AN UPPER LEVEL TROUGH TUESDAY
FOR SHOWERS AND COOLER WEATHER. SHOWERS WILL DIMINISH THURSDAY AS
WEAK RIDGING BUILDS OVER THE AREA AHEAD OF A FRONTAL SYSTEM THAT
WILL AFFECT THE AREA ON FRIDAY.

&&

.SHORT TERM...THE WARM FRONT THAT HAS BROUGHT RAIN AT TIMES TO THE
COAST AND NORTHERN INTERIOR OVER THE LAST DAY WILL SHIFT INTO
BRITISH COLUMBIA TODAY AS A COLD FRONT APPROACHES FROM THE WEST.
EXPECT ONE MORE DAY OF RELATIVELY MILD TEMPERATURES TODAY. EVENING
MODEL RUNS WERE A BIT SLOWER WITH THE FRONTAL PASSAGE TONIGHT...BUT
SILL SPREAD RAIN THROUGH INTO THE INTERIOR LATE IN THE EVENING AND
INTO THE CASCADES BY EARLY TUESDAY MORNING. EXPECT BREEZY CONDITIONS
TONIGHT AS THE FRONT WORKS THROUGH THE INTERIOR...FOLLOWED BY
SHOWERS AND BREEZY CONDITIONS AGAIN TUESDAY BEHIND THE FRONT.
HEIGHTS ON TUESDAY WILL FALL SIGNIFICANTLY WITH HIGH TEMPERATURES
PEAKING IN THE LOW TO MID 50S AND SNOW LEVELS DROPPING TO AROUND
3000 FT. MESOSCALE MODELS CONTINUE TO ADVERTISE THE DEVELOPMENT OF A
PUGET SOUND CONVERGENCE ZONE IN THE POST FRONTAL WESTERLY FLOW
TUESDAY AND TUESDAY EVENING. IN ADDITION...THE CURRENT FORECAST
PACKAGE CONTINUES TO HIGHLIGHT A CHANCE OF THUNDERSTORMS OVER MUCH
OF THE AREA TUESDAY AFTERNOON AS THE COOLER AIR ALOFT MOVES OVER
WESTERN WASHINGTON. LOWER SNOW LEVELS AND ENHANCED PRECIPITATION
ASSOCIATED WITH A PUGET SOUND CONVERGENCE ZONE OVER THE CASCADES OF
SNOHOMISH AND KING COUNTIES MAY EQUATE TO ADVISORY LEVEL
ACCUMULATIONS THROUGH TUESDAY EVENING.

SHOWERS WILL GENERALLY DIMINISH WEDNESDAY AS THE UPPER LEVEL TROUGH
SHIFTS INTO THE NORTHERN INTERMOUNTAIN AREA. MODELS CONTINUE TO SHOW
A SHORTWAVE TROUGH DIGGING INTO OREGON LATE WEDNESDAY AFTERNOON OR
EVENING THAT WILL LIKELY BOOST SHOWERS. HIGH TEMPERATURES WILL
REMAIN IN THE LOW 50S WEDNESDAY.

.LONG TERM...MEDIUM RANGE MODELS CONTINUE TO SHOW UPPER LEVEL
RIDGING ON THURSDAY AS A DEEP UPPER LEVEL LOW MOVES INTO THE GULF OF
ALASKA. THE BRIEF RIDGING ON THURSDAY WILL LIKELY GIVE THE A BREAK
IN THE SHOWERS BEFORE A FRONT ARRIVES FRIDAY. BOTH THE GFS AND ECMWF
DIFFER ON THE TRACK OF THE TRAILING UPPER LEVEL LOW. THE EUROPEAN
BRINGS IT DOWN THE NORTHWEST COAST BEFORE OPENING UP AND MOVING INTO
NORTHERN CALIFORNIA MONDAY NIGHT. THE GFS TAKES A MUCH MORE
PROGRESSIVE TACK...OPENING THE LOW UP AND BRINGING IT INTO BRITISH
COLUMBIA SATURDAY AFTERNOON. THE CURRENT FORECAST CONTINUES TO
REFLECT A COOL AND UNSETTLED PATTERN THROUGH THE WEEKEND.

&&

.HYDROLOGY...FLOODING IS UNLIKELY OVER THE NEXT 7 DAYS.

&&

.AVIATION...A FLAT UPPER RIDGE OVER THE REGION THIS MORNING WILL
MOVE EAST...WHILE A COLD FRONT MOVES INTO THE COASTAL WATERS TODAY
AND ACROSS WESTERN WASHINGTON TONIGHT. THE FLOW ALOFT WILL BE
SOUTHWEST. THE AIR MASS WILL BE MOIST BELOW 10000 FT...AND IT WILL
BECOME WEAKLY UNSTABLE TONIGHT.

MOSTLY VFR CONDITIONS ACROSS THE FORECAST AREA EARLY THIS MORNING
WITH SCT030 OVC060-080 AND AREAS OF LIGHT RAIN -- MAINLY ALONG THE
COAST AND IN THE NORTH INTERIOR. ON THE WHOLE THERE WILL NOT BE MUCH
CHANGE TODAY. CONDITIONS WILL DETERIORATE TO MVFR AND LOCAL IFR LATE
TONIGHT AS A COLD FRONT MOVES ACROSS THE AREA.

KSEA...SOUTH WIND 6-12 KT TODAY...BECOMING SOUTHWEST 12-16 KT
GUSTING 24 KT THIS EVENING.   MCDONNAL

&&

.MARINE...A RIDGE OVER WESTERN WASHINGTON WILL WEAKEN THIS MORNING
AS A COLD FRONT MOVES INTO THE COASTAL WATERS. THE FRONT WILL MOVE
INLAND THIS EVENING...FOLLOWED BY STRONG ONSHORE FLOW LATER TONIGHT
AND TUESDAY. SMALL CRAFT ADVISORY CONDITIONS WILL PREVAIL THROUGH
THIS PERIOD. THE STRENGTH OF THE ONSHORE FLOW MAKES WESTERLY GALES
IN THE CENTRAL AND EASTERN STRAIT OF JUAN DE FUCA APPEAR LIKELY LATE
THIS EVENING INTO TUESDAY...AND CONFIDENCE IS HIGH ENOUGH TO UPGRADE
THE GALE WATCH TO A WARNING. PSPC VANCOUVER HAS A GALE WARNING IN
EFFECT AS WELL.

THERE WILL BE A WESTERLY SWELL OF 10 TO 12 FT OVER THE COASTAL
WATERS THROUGH TUESDAY. BAR CONDITIONS WILL BE ROUGH AS WELL.

ONSHORE FLOW WILL WEAKEN WEDNESDAY AND THURSDAY AS A RIDGE BUILDS
OVER THE REGION. A RELATIVELY WEAK FRONT WILL PROBABLY REACH THE
AREA FRIDAY.   MCDONNAL

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS...ENTRANCES TO THE
       STRAIT...ADMIRALTY INLET...NORTHERN INLAND WATERS...PUGET
       SOUND AND HOOD CANAL.
     GALE WARNING CENTRAL STRAIT OF JUAN DE FUCA AND EAST ENTRANCE
       STRAIT THIS EVENING THROUGH TUESDAY AFTERNOON.
     SMALL CRAFT ADVISORY GRAYS HARBOR FOR ROUGH BAR.

&&

$$

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









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