Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 170500
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
955 PM PDT THU APR 16 2015

.SYNOPSIS...AN UPPER LEVEL RIDGE WILL KEEP SKIES MOSTLY CLEAR
TONIGHT WITH COOL TEMPERATURES. A WEAK DRY UPPER LEVEL TROUGH WILL
BRING PERIODS OF CLOUDS TO WESTERN WASHINGTON ON FRIDAY. A STRONGER
UPPER LEVEL RIDGE WILL BRING MOSTLY SUNNY AND WARMER WEATHER
SATURDAY THROUGH TUESDAY. A LARGE UPPER LEVEL TROUGH WILL BRING
SHOWERS TO THE AREA TUESDAY NIGHT THROUGH THURSDAY.

&&

.SHORT TERM...SATELLITE IMAGERY SHOWS UPPER LEVEL RIDGE AXIS HAS
MOVED EAST OF THE AREA TONIGHT. UPPER LEVEL TROUGH OFFSHORE AROUND
133W AT 04Z SLOWLY MOVING EASTWARD. WITH THE TROUGH WELL OFFSHORE
SKIES ARE CLEAR OVER WESTERN WASHINGTON THIS EVENING. TEMPERATURES
AT 04Z RANGED FROM THE MID 40S TO THE MID 50S.

UPPER LEVEL TROUGH CONTINUING TO MOVE EAST TONIGHT BUT WILL STILL BE
FAR ENOUGH OFFSHORE BY FRIDAY MORNING TO KEEP SKIES MOSTLY CLEAR
OVERNIGHT. LOWS WILL BE MOSTLY IN THE 40S.

WHAT IS LEFT OF THE UPPER LEVEL TROUGH MOVING THROUGH WESTERN
WASHINGTON ON FRIDAY. MODEL CROSS SECTIONS SHOW ONLY SOME MID LEVEL
CLOUDS ASSOCIATED WITH THE TROUGH AS IT MOVES ACROSS THE AREA. WILL
STAY WITH THE DRY FORECAST FOR FRIDAY. FLOW ALOFT TURNING
NORTHWESTERLY BEHIND THE FRONT. WITH THE AIR MASS SLIGHTLY UNSTABLE
SOME SC COULD FORM LATE IN AFTERNOON INTO THE EVENING HOURS. EVEN
WITH THE COMBINATION OF THE MID LEVEL CLOUDS AND THE SC LATE IN THE
DAY MOSTLY SUNNY WORDING FOR FRIDAY LOOKS GOOD. HIGHS WILL MOSTLY BE
IN THE LOWER TO MID 60S.

UPPER LEVEL RIDGE BUILDING QUICKLY OFFSHORE FRIDAY NIGHT WITH THE
SURFACE GRADIENTS GOING NORTHWESTERLY. GFS HAS KOLM-KBLI GRADIENT
APPROACHING -2 MB. MODEL CROSS SECTIONS SHOW A VERY SHALLOW LAYER OF
MOISTURE OVER THE INTERIOR SATURDAY MORNING BUT WITH THE INCREASING
NORTHERLY GRADIENTS AND THE WINDS RIGHT OFF THE GROUND NORTHERLY AT
15 KNOTS WILL STAY WITH THE IDEA OF THE MORNING LOW CLOUDS MAINLY
CONFINED TO THE COAST. WITH PLENTY OF SUNSHINE IN THE AFTERNOON
HIGHS IN THE 60S WILL BE COMMON.

DRY AND WARM WEATHER CONTINUING ON SUNDAY AS THE UPPER RIDGE
OFFSHORE BUILDS INLAND. 850 MB TEMPERATURES WARMING TO AROUND PLUS
10C. WITH THE WARMING ALOFT THE WARMER LOCATIONS ON SUNDAY SHOULD
GET INTO THE THE LOWER 70S. FORECAST ON TRACK TONIGHT. FELTON

.LONG TERM...PREVIOUS DISCUSSION FOLLOWS. THE UPPER LEVEL RIDGE AXIS
WILL MOVE OVER THE COAST SUNDAY NIGHT...THEN SHIFT SLOWLY E OVER E
WA ON TUESDAY. WEAK LOW LEVEL OFFSHORE FLOW WILL PUT MAX TEMPS IN
THE 60S TO MID 70S MONDAY AND TUESDAY.

THE GFS...ECMWF...AND CANADIAN CONTINUE TO BE A BIT OF AN
INCONSISTENT MESS FROM TUESDAY NIGHT ONWARD. THERE IS BROAD
AGREEMENT THAT THE UPPER LEVEL RIDGE WILL DRIFT E AND A LARGE UPPER
LEVEL TROUGH WILL APPROACH THE COAST. MOIST S FLOW WILL DEVELOP OVER
W WA AHEAD OF THE TROUGH FOR SOME SHOWERS...BUT JUST WHEN THIS WILL
WILL OCCUR AND HOW IT WILL UNFOLD IS STILL IN DOUBT. SO FOR
NOW...THE TUESDAY NIGHT THROUGH THURSDAY PERIOD HAS A BROADBRUSH
CHANCE OF SHOWERS. KAM

&&

.AVIATION...HIGH PRESSURE OVER THE PAC NW WILL LEAD TO DRY AND
STABLE WEATHER ACROSS WESTERN WA TONIGHT. THE FLOW ALOFT IS
WESTERLY. VFR CONDITIONS WILL CONTINUE. A WEAK COLD FRONT WILL CROSS
THE AREA ON FRIDAY BUT THERE IS LITTLE MOISTURE ATTACHED WITH THIS
SYSTEM. EXPECT VFR CONDITIONS. 33

KSEA...FEW HIGH CLOUDS TONIGHT WITH LIGHT N/NE WINDS. 33

&&

.MARINE...HIGH PRESSURE WILL REMAIN OVER THE AREA TONIGHT. WEST
SWELLS ARE 10 TO 13 FT AND A SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS
REMAINS IN EFFECT FOR THE COASTAL WATERS AND WESTERN STRAIT OF JUAN
DE FUCA. MEANWHILE...NORTH WINDS AT DESTRUCTION ARE STILL OVER 20 KT
BUT WINDS SHOULD EASE AFTER MIDNIGHT TONIGHT.

ONSHORE FLOW WILL INCREASE ON FRIDAY AS A COLD FRONT CROSSES WESTERN
WA. THE COASTAL WATERS WILL LIKELY SEE SMALL CRAFT ADVISORY
WINDS...WITH GALES POSSIBLE THROUGH THE CENTRAL AND EAST STRAIT.

LOW PRESSURE WILL FORM ALONG THE COAST THIS WEEKEND FOR NORTHERLY
FLOW. OFFSHORE FLOW WILL CONTINUE ON MONDAY. THE NEXT FRONT WILL
ARRIVE NEXT TUESDAY. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY COAST AND WEST ENTRANCE FOR HAZARDOUS SEAS.
     SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR.
     GALE WATCH FRIDAY EVENING CENTRAL AND EAST STRAIT.

&&

$$

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