Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 160953
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
300 AM PDT THU APR 16 2015

.SYNOPSIS...AN UPPER RIDGE WILL BRING MOSTLY SUNNY DAYS TO WESTERN
WASHINGTON TODAY THROUGH TUESDAY. ONE EXCEPTION IS A WEAK UPPER
TROUGH MOVING THROUGH BRITISH COLUMBIA LATE FRIDAY AND FRIDAY NIGHT
WHICH COULD PRODUCE SOME LIGHT SHOWERS OVER THE CASCADES. HIGHS WILL
BE IN THE UPPER 50S TO 60S THROUGH SATURDAY...AND IN THE 60S TO
LOWER 70S SUNDAY THROUGH TUESDAY. SHOWERS ARE POSSIBLE WEDNESDAY.

&&

.SHORT TERM...AN UPPER RIDGE REMAINS OVER WASHINGTON EARLY THIS
MORNING...EXTENDING ACROSS THE AREA FROM THE UPPER HIGH CENTERED
WELL OFFSHORE OF CALIFORNIA. A WARM FRONT IS ALONG THE BRITISH
COLUMBIA COAST WITH A FRONTAL BOUNDARY EXTENDING SOUTHWEST ALONG THE
NORTHWEST SIDE OF THE RIDGE. THE RIDGE IS KEEPING SKIES OVER WESTERN
WASHINGTON MOSTLY CLEAR...AND 2 AM TEMPERATURES RANGED FROM THE MID
30S TO THE UPPER 40S. LIGHT PATCHY FOG WILL PROBABLY DEVELOP OVER
THE SOUTH PUGET SOUND REGION...SOUTHWEST INTERIOR...AND LOWER
CHEHALIS VALLEY AROUND SUNRISE.

THE UPPER RIDGE WILL BUILD NORTHWARD OVER THE AREA TODAY...PUSHING
THE FRONTAL BAND FURTHER AWAY FROM THE FORECAST AREA. THE FORECAST
AREA SHOULD HAVE LOTS OF SUNSHINE TODAY. THE AIR MASS WILL BE
SEVERAL DEGREES WARMER THAN IT WAS WEDNESDAY...WITH A LIGHT
NORTHWEST PRESSURE GRADIENT ACROSS WESTERN WASHINGTON. HIGHS TODAY
SHOULD BE IN THE UPPER 50S TO 60S.

THE UPPER RIDGE WILL PROGRESS EAST OF THE AREA TONIGHT...AND THE
WEAK UPPER TROUGH WITH THE FRONTAL SYSTEM TO OUR NORTH WILL BRUSH
WESTERN WASHINGTON AS IT MOVES THROUGH BRITISH COLUMBIA LATE FRIDAY.
THE TROUGH WILL BRING SOME MID LEVEL MOISTURE AND INCREASE LOW LEVEL
ONSHORE FLOW...RESULTING IN SOME CLOUD COVER ESPECIALLY AT THE COAST
AND IN THE MOUNTAINS. BUT IT WILL STILL BE A PARTLY TO MOSTLY SUNNY
DAY...AND HIGHS AGAIN WILL BE IN THE UPPER 50S TO 60S.

A STRONGER OFFSHORE UPPER RIDGE WILL BUILD ALONG 130W SATURDAY...
WITH DRIER NORTHWEST FLOW ALOFT. LOW LEVEL FLOW WILL VEER TO
NORTHWESTERLY AS WELL. ANY LOW CLOUD COVER LINGERING IN THE MORNING
SHOULD BE SHORT LIVED...AND SATURDAY WILL BE ANOTHER DAY OF SUNNY
AND SLIGHTLY WARMER WEATHER.   MCDONNAL

.LONG TERM...THE UPPER RIDGE WILL WEAKEN SLIGHTLY AS IT MOVES SLOWLY
INTO THE OFFSHORE WATERS SUNDAY AND THEN INLAND MONDAY AND TUESDAY.
THE LOWER REACHES OF THE AIR MASS WILL BE A LITTLE WARMER AS THE
RIDGE MOVES INLAND...WITH HIGHS IN THE MID 60S TO LOWER 70S ACROSS
MOST OF WESTERN WASHINGTON.

THE MODELS ARE IN ROUGH AGREEMENT THAT MOIST SOUTHERLY FLOW WILL
DEVELOP OVER THE AREA LATE TUESDAY OR TUESDAY NIGHT...AS THE UPPER
RIDGE MOVES EAST AND A DEEP UPPER LOW MOVES SOUTHEAST WELL OFFSHORE.
THAT SHOULD PRODUCE SOME SHOWERS OVER THE FORECAST AREA...ESPECIALLY
OVER THE HIGHER TERRAIN.   MCDONNAL

&&

.AVIATION...AN UPPER LEVEL RIDGE OVER THE PAC NW WILL MAINTAIN DRY
AND STABLE WEATHER ACROSS WESTERN WA TODAY. THE FLOW ALOFT IS
WESTERLY. VFR CONDITIONS WILL CONTINUE. 33

KSEA...FEW CIRRUS CLOUDS ALOFT THIS MORNING WITH VFR CONDITIONS.
LIGHT N/NE WINDS AT THE SURFACE. 33

&&

.MARINE...HIGH PRESSURE OVER WESTERN WA WILL BRING GENERALLY LIGHT
WINDS THROUGH TONIGHT. MEANWHILE...WEST SWELLS WILL BUILD TO 10-13
FT TODAY AND A SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS IS IN EFFECT
FOR THE COASTAL WATERS AND WESTERN STRAIT OF JUAN DE FUCA. ONSHORE
FLOW WILL INCREASE ON FRIDAY AS A COLD FRONT CROSSES WESTERN WA.
SMALL CRAFT ADVISORY WINDS ARE LIKELY FOR THE COASTAL WATERS AND THE
STRAIT OF JUAN DE FUCA LATE FRIDAY AFTERNOON AND EVENING. NORTHERLY
FLOW WILL DEVELOP SATURDAY AND SUNDAY AS LOW PRES FORMS ALONG THE
COAST. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COASTAL WATERS FOR HAZARDOUS SEAS.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.

&&

$$

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




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