Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 222204
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 PM PDT WED APR 22 2015

.SYNOPSIS...HIGH PRESSURE WILL GIVE MOSTLY DRY CONDITIONS TONIGHT. A
WEAK FRONT WILL MOVE THROUGH THE REGION THURSDAY. THE FRONT WILL BE
FOLLOWED BY AN UPPER LEVEL LOW AND ONSHORE FLOW FOR SHOWERY AND COOL
CONDITIONS FRIDAY AND SATURDAY. AFTER A MOSTLY DRY SUNDAY...A WARM
FRONT WILL BRUSH THE AREA SUNDAY NIGHT. EARLY NEXT WEEK LOOKS DRY
AND WARM WITH A CHANCE OF SHOWERS RETURNING BY WEDNESDAY.

&&

.SHORT TERM...THE FEW REMAINING SHOWERS HAVE ENDED. THE CUMULUS
FIELD OVER LAND AREAS WILL PERSIST INTO THE EVENING THEN DISSIPATE
AFTER SUNSET. HIGH CLOUDS FROM AN APPROACHING FEATURE ARE ALREADY
APPARENT. RAIN COULD BEGIN ON THE COAST AS EARLY AS MIDNIGHT TONIGHT
BUT WILL PROBABLY NOT START UNTIL LATE TONIGHT OR EARLY THURSDAY
MORNING.

RAIN WILL SPREAD INLAND DURING THE DAY BUT THE SYSTEM DOES NOT LOOK
WELL ORGANIZED SO HAVE KEPT POPS FOR MOST AREAS IN THE LIKELY
CATEGORY. THERE IS A BETTER CHANCE OF RAIN OVER THE MOUNTAINS AND
COAST. SHOWERS WILL TAPER A BIT THURSDAY NIGHT. THEN AN UPPER LEVEL
LOW WILL MOVE SLOWLY SOUTHEAST OUT OF THE GULF OF ALASKA. IT WILL
CROSS WESTERN WASHINGTON ON FRIDAY NIGHT AND SATURDAY AND WILL NOT
EXIT THE REGION UNTIL SATURDAY NIGHT. THE WEATHER WILL BE SHOWERY
THOUGH ON FRIDAY AFTERNOON THE SHOWERS LOOK ORGANIZED ENOUGH TO CALL
IT RAIN. LIKELY POPS FRIDAY WILL TAPER TO CHANCE SATURDAY.

HIGH TEMPERATURES ALL THREE DAYS THURSDAY THROUGH SATURDAY WILL BE
IN THE 50S. THE UPPER LOW HAS HEIGHTS AROUND 540 DM SO THE SNOW
LEVEL IN THE MOUNTAINS WILL FALL AS LOW AS 3000 FEET. A FEW INCHES
OF SNOW ARE POSSIBLE AT TIMES IN THE PASSES. BURKE

.LONG TERM...IN EARLIER MODEL RUNS A VERY WET SYSTEM REACHED THE
AREA ON SUNDAY. THAT SYSTEM IS NOWHERE TO BE FOUND IN RECENT RUNS.
IN FACT SUNDAY IS MOSTLY DRY IN THE GFS WITH WARM FRONTAL RAIN JUST
TOUCHING THE COAST IN THE AFTERNOON. THE EURO IS MORE PROGRESSIVE
AND HAS RAIN EVERYWHERE SUNDAY AFTERNOON. HAVE CUT POPS BACK TO
CHANCE INLAND AND LIKELY ON THE COAST FROM THE EARLIER CATEGORICAL
LEVELS. HEIGHTS RISE SIGNIFICANTLY SUNDAY SO HIGH TEMPERATURES WILL
REACH THE LOW 60S OVER INLAND AREAS.

THE WARM FRONT BRUSHES THE AREA SUNDAY NIGHT AND THEN IS SHOVED
NORTH BY A BUILDING RIDGE. MONDAY AND TUESDAY APPEAR MOSTLY DRY AND
WARMER WITH HIGHS REACHING THE UPPER 60S MONDAY AND THE LOW 70S
TUESDAY. SHOWERS RETURN NEXT WEDNESDAY. BURKE

&&

.AVIATION...WESTERLY FLOW ALOFT OVER WESTERN WASHINGTON THIS
AFTERNOON WILL CONTINUE TONIGHT AS A FLAT UPPER RIDGE MOVES ACROSS
THE PACIFIC NORTHWEST...THEN BACK TO SOUTHWEST THURSDAY AS A FRONT
MOVES INTO THE FORECAST AREA. LOW LEVEL ONSHORE FLOW WILL GRADUALLY
WEAKEN THROUGH THE PERIOD. THE AIR MASS WILL REMAIN SOMEWHAT MOIST
BELOW 5000 FT TONIGHT...WITH INCREASING MOISTURE ALL LEVELS THURSDAY.

SKIES ACROSS WESTERN WASHINGTON ARE PARTLY CLOUDY THIS AFTERNOON
WITH ONLY A FEW SPOTS REPORTING A CEILING BKN045-060. HIGH CLOUDS
WILL INCREASE TONIGHT...THEN GRADUALLY LOWER THURSDAY. CONDITIONS
WILL EVENTUALLY DETERIORATE TO WIDESPREAD MVFR AND LOCAL IFR
THURSDAY AFTERNOON AS THE FRONT BRINGS RAIN TO THE AREA.

KSEA...SOUTHERLY WIND 5-10 KT WILL PROBABLY SWITCH TO NORTHWEST LATE
THIS AFTERNOON OR EVENING FOR SEVERAL HOURS...THEN SWITCH BACK TO
SOUTHERLY AROUND MIDNIGHT AND INCREASE TO 8-14 KT THURSDAY
AFTERNOON.   MCDONNAL

&&

.MARINE...ONSHORE FLOW WILL EASE TONIGHT AS HIGH PRESSURE MOVES FROM
THE OFFSHORE WATERS INTO WESTERN WASHINGTON. MARGINAL SMALL CRAFT
ADVISORY WINDS WILL CONTINUE THIS EVENING FOR ADMIRALTY INLET AND
NORTHERN INLAND WATERS...WITH 15 TO 30 KT SMALL CRAFT ADVISORY
WESTERLIES THROUGH TONIGHT OVER THE CENTRAL AND EASTERN STRAIT OF
JUAN DE FUCA.

A COLD FRONT WILL MOVE THROUGH THE AREA FROM THE WEST THURSDAY. IT
SHOULD PRODUCE SMALL CRAFT ADVISORY SOUTHERLIES FOR ALL MARINE ZONES
EXCEPT THE CENTRAL STRAIT...WITH A BRIEF BURST OF POST-FRONTAL SMALL
CRAFT ADVISORY WESTERLIES IN THE CENTRAL AND EASTERN STRAIT THURSDAY
EVENING.

A WEAK TROUGH WILL MOVE THROUGH THE AREA FRIDAY AND FRIDAY NIGHT.
MODELS HAVE BEEN INCONSISTENT FOR SATURDAY AND BEYOND...BUT IT NOW
LOOKS LIKE A WEAK FRONTAL SYSTEM WILL AFFECT THE FORECAST AREA
SUNDAY AS IT MOVES INTO BRITISH COLUMBIA...AND HIGH PRESSURE WILL
BUILD OVER THE REGION MONDAY.   MCDONNAL

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COAST...CENTRAL AND EASTERN STRAIT OF JUAN
       DE FUCA...ADMIRALTY INLET...NORTHERN INLAND WATERS.

&&

$$

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




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