Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 212208
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT TUE APR 21 2015

.SYNOPSIS...A FRONT WILL MOVE INLAND THIS EVENING BRINGING A CHANGE
IN THE WEATHER. COOL AND LOCALLY WINDY CONDITIONS WITH SHOWERS ARE
LIKELY TONIGHT INTO WEDNESDAY. SNOW LEVELS WILL FALL TONIGHT AND
WEDNESDAY IN THE MOUNTAINS. A WEAK FRONT WILL ARRIVE THURSDAY
BRINGING A CHANCE OF RAIN. MOIST SOUTHWEST FLOW ALOFT WILL BRING
PERIODS OF RAIN NEXT WEEKEND.

&&

.SHORT TERM...RADAR ECHOES SHOW LIGHT RAIN MOVING ONTO THE COAST
WHICH WILL SPREAD INLAND THIS EVENING. THE FRONT IS NOT TOO STRONG
SO HAVE LIMITED POPS TO LIKELY OVER NORTHERN AND WESTERN SECTIONS
TONIGHT...WITH CHANCE POPS ELSEWHERE. WINDY CONDITIONS HAVE ALREADY
DEVELOPED OVER THE EASTERN STRAIT AND ON WHIDBEY ISLAND. A WIND
ADVISORY IS IN EFFECT FOR THE EASTERN STRAIT AND ADMIRALTY INLET
AREA.

A CONVERGENCE ZONE WILL DEVELOP LATER TONIGHT AFTER THE FRONT
PASSES. THIS WILL KEEP LIKELY POPS IN THE FORECAST OVER THE CENTRAL
PUGET SOUND AREA GOING ALL NIGHT. THE FRONT WILL LOSE ITS STRENGTH
WEDNESDAY WITH ONLY CHANCE POPS OVER MOST AREAS...AND PERHAPS STILL
A WEAK PSCZ SIGNATURE. WITH LOTS OF CLOUDS AROUND AND SIGNIFICANTLY
LOWER HEIGHTS...HIGHS WEDNESDAY WILL BE IN THE MID AND UPPER 50S.

DRYING AND CLEARING IS LIKELY WEDNESDAY NIGHT WITH A RIDGE BUILDING
AT BOTH THE SURFACE AND UPPER LEVELS. THE NEXT WEAK SYSTEM WILL
ARRIVE THURSDAY WITH SHOWERS LIKELY COAST AND MOUNTAINS AND CHANCE
POPS ELSEWHERE. ANOTHER WEAK IMPULSE ARRIVES FRIDAY. HIGHS BOTH
THURSDAY AND FRIDAY WILL BE IN THE MID 50S.

THE SNOW LEVEL WILL FALL TO 3500 FEET OR SO BY WEDNESDAY. QPF IS NOT
HIGH SO THE IMPACTS TO MOST TRAVELERS THIS WEEK WILL BE AN INCH OR
TWO OF SNOW AT TIMES IN THE HIGHER PASSES. BURKE

.LONG TERM...A WARMER AND WETTER SYSTEM ARRIVES FROM THE SOUTHWEST
SATURDAY NIGHT. RAIN AT TIMES IS LIKELY THROUGH MONDAY. THE SNOW
LEVEL WILL RISE TO 6500 FEET OR SO. MODEL QPF IS 2-3 INCHES IN THE
MOUNTAINS OVER ABOUT 48 HOURS WITH 0.5-1.5 INCH IN THE LOWLANDS.
THIS WILL PROBABLY NOT BE THE MOST PLEASANT OF WEEKENDS IN THE
MOUNTAINS. TUESDAY LOOKS COOLER AND MORE SHOWERY. BURKE

&&

.AVIATION...SOUTHWEST FLOW ALOFT WILL CONTINUE OVER WESTERN
WASHINGTON THIS EVENING WITH A COLD FRONT MOVING INLAND. AN UPPER
TROUGH WILL MOVE THROUGH THE AREA LATER TONIGHT...WITH FLOW ALOFT
VEERING TO NORTHWEST BEHIND THE TROUGH ON WEDNESDAY. STRONG ONSHORE
FLOW WILL CONTINUE...AND THE AIR MASS WILL REMAIN MOIST.

SKY COVER ACROSS THE FORECAST AREA IS ROUGHLY SCT-BKN035 BKN-OVC070
WITH LOCAL OVC025-035. THE RADAR SHOWS AREAS OF PRECIPITATION MAINLY
OVER THE OLYMPIC PENINSULA AND ALONG THE COAST. CONDITIONS SHOULD
GRADUALLY DETERIORATE TONIGHT AS THE FRONT MOVES INLAND...FOLLOWED
BY MOIST ONSHORE FLOW. MOST OF THE FORECAST AREA SHOULD HAVE MVFR TO
LOCAL IFR CEILINGS FROM LATE THIS EVENING THROUGH WEDNESDAY MORNING.
THERE SHOULD BE GRADUAL IMPROVEMENT WEDNESDAY AFTERNOON.

KSEA...SOUTHWEST WIND 6-12 KT...OCCASIONALLY SWITCHING TO NORTHWEST
LATE THIS AFTERNOON AND THIS EVENING. THE WIND FORECAST AT KSEA IS
HIGHLY UNCERTAIN...BECAUSE IT WILL BE NEAR THE LINE WHERE
NORTHERLIES COMING FROM THE NORTH SOUND MEET WITH THE
SOUTHWESTERLIES COMING THROUGH THE SOUTH SOUND. THERE COULD ALSO BE
PERIODS WHEN KSEA AND KBFI HAVE OPPOSING WINDS. THE CEILING AT KSEA
WILL PROBABLY LOWER TO 2000 TO 3000 FT LATER TONIGHT.   MCDONNAL

&&

.MARINE...STRONG ONSHORE FLOW WILL CONTINUE TONIGHT IN THE WAKE OF A
COLD FRONT MOVING INLAND. WESTERLY GALES DEVELOPED IN THE CENTRAL
AND EASTERN STRAIT OF JUAN DE FUCA LATE THIS MORNING. GALES WILL
CONTINUE THROUGH TONIGHT...WITH 35 TO 45 KT WINDS OVER PARTS OF
THOSE MARINE ZONES THROUGH AROUND MIDNIGHT. MARGINAL GALES ARE ALSO
LIKELY OVER THE NORTHWEST PART OF THE COASTAL WATERS...WITH SMALL
CRAFT ADVISORY WINDS FOR ALL OTHER MARINE ZONES.

ONSHORE FLOW WILL EASE SOMEWHAT WEDNESDAY AND WEDNESDAY NIGHT AS
HIGH PRESSURE SHIFTS INTO WESTERN WASHINGTON. HOWEVER SMALL CRAFT
ADVISORY WINDS WILL CONTINUE THROUGH WEDNESDAY AT LEAST FOR MUCH OF
THE FORECAST AREA. ANOTHER WEAK FRONT WILL MOVE ACROSS THE AREA
THURSDAY AND THURSDAY NIGHT...AND IT WILL BE FOLLOWED BY RELATIVELY
WEAK ONSHORE FLOW. A STRONGER FRONTAL SYSTEM WILL AFFECT THE AREA
SATURDAY AND SUNDAY.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...WIND ADVISORY UNTIL 1 AM WEDNESDAY FOR EASTERN STRAIT OF JUAN
      DE FUCA AND ADMIRALTY INLET AREAS.
PZ...GALE WARNING TONIGHT CENTRAL AND EASTERN STRAIT.
    .GALE WARNING TONIGHT COASTAL WATERS ZONES 150 170 173.
    .SMALL CRAFT ADVISORY COASTAL ZONES 153 156 176...WESTERN STRAIT
       OF JUAN DE FUCA...ADMIRALTY INLET...NORTHERN INLAND WATERS...
       PUGET SOUND AND HOOD CANAL.
    .SMALL CRAFT ADVISORY FOR ROUGH BAR GRAYS HARBOR.

&&

$$

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





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