Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 050337
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
837 PM PDT TUE AUG 4 2015

.SYNOPSIS...AN UPPER TROUGH WILL BRING SOME SHOWERS WEDNESDAY.
DRIER AND WARMER WEATHER WILL PREVAIL THURSDAY AND FRIDAY WITH
HIGH PRESSURE ALOFT IN CONTROL. ANOTHER UPPER TROUGH WILL BRING
SOME SHOWERS OVER THE WEEKEND.

&&

.SHORT TERM...CLOUDS WILL INCREASE TONIGHT UNDER THE INFLUENCE
OF LEVEL ONSHORE FLOW AHEAD OF AN APPROACHING UPPER TROUGH. THE
UPPER TROUGH WILL MOVE OVER WESTERN WASHINGTON ON WEDNESDAY...
BRINGING SOME SHOWERS...MAINLY OVER THE MOUNTAINS IN THE
AFTERNOON. HIGHS WILL WILL COOL SEVERAL DEGREES AND IT SHOULD BE
MOSTLY CLOUDY ALL DAY.

A WEAK UPPER RIDGE WILL MOVE OVER THE AREA THURSDAY AND FRIDAY.
THIS WILL END THE SHOWER THREAT. THERE SHOULD BE AFTERNOON
SUNSHINE THURSDAY AFTER MORNING CLOUDS. FRIDAY LOOKS MOSTLY SUNNY
ALL DAY WITH NORTHERLY LOW LEVEL FLOW. HIGHS SHOULD WARM TO NEAR
NORMAL AGAIN ON THURSDAY AND THEN PROBABLY BUMP UP AT LEAST A FEW
MORE DEGREES ON FRIDAY. SCHNEIDER

.LONG TERM...AN UPPER TROF WILL DOMINATE THE WEATHER PATTERN OVER
THE PACIFIC NORTHWEST DURING THIS PERIOD. THE MAIN DIFFERENCES IN
THE MEDIUM RANGE SOLUTIONS CONCERNED THE DETAILS. HOWEVER...THE
OVERALL MESSAGE WAS THE SAME. ANTICIPATE COOL AND UNSETTLED
CONDITIONS SATURDAY THROUGH TUE. TEMP GUIDANCE APPEARED TOO
WARM...SO UNDERCUT THE MODELS AND KEPT MAX TEMPS BELOW CLIMO.

&&

.AVIATION...AN UPPER LEVEL LOW OVER THE CENTRAL B.C. COAST AT 03Z
WILL MOVE SE DOWN THE B.C. COAST AND OVER SW B.C. BY 00Z WEDNESDAY
AFTERNOON. STRONG ONSHORE FLOW HAS DEVELOPED TONIGHT WHICH WILL PUSH
MORE MARINE AIR OVER THE W WA INTERIOR OVERNIGHT. AREAS OF MAINLY
MVFR STRATUS ARE EXPECTED TO FORM ONCE AGAIN AROUND 12Z. CIGS WILL
LIFT WEDNESDAY AFTERNOON...BUT THE APPROACHING UPPER LEVEL LOW WILL
PROVIDE ENOUGH LIFT TO MAINTAIN VFR BKN CIGS AFTER 18Z. SCATTERED
SHOWERS SHOULD DEVELOP IN THE AFTERNOON AS THE LOW MOVES DOWN OVER
CYVR.

KSEA...GOOD VFR CONDITIONS SHOULD CONTINUE UNTIL AROUND 11Z WHEN
MVFR STRATUS SHOULD BEGIN FORMING. THE STRATUS WILL LIFT IN THE LATE
MORNING AND AFTERNOON FOR LAYERS SCT-BKN030 BKN050 AND A FEW
SHOWERS. SURFACE WINDS WILL REMAIN S-SW 5-10 KT. KAM

&&

.MARINE...MODERATE TO STRONG ONSHORE FLOW WILL CONTINUE ACROSS W WA
THIS WEEK...BETWEEN A LARGE SURFACE RIDGE OVER THE NE PACIFIC AND
LOWER PRESSURE OVER E WA. WITH STRONG ONSHORE FLOW TONIGHT A GALE
WARNING IS ALREADY UP FOR THE C/E STRAIT OF JUAN DE FUCA. SUSTAINED
WINDS HAVE MADE IT TO 32 KT AT RACE ROCKS ALREADY SO THERE REMAINS A
DECENT CHANCE THAT WINDS WILL RISE TO GALE LEVELS LATER THIS
EVENING. NW WINDS IN THE N PART OF ADMIRALTY INLET HAVE ALREADY
REACHED SCA LEVELS.

PER THE 18Z GFS THE UIL-BLI PRESSURE GRADIENT SHOULD BE A LITTLE
WEAKER WEDNESDAY NIGHT COMPARED TO TONIGHT. THE CURRENT FORECAST
LOOKS FINE FOR THE C/E STRAIT WITH HIGH END SCA WINDS 20-30 KT.

A WEAK RIDGE WILL FORM JUST OFFSHORE THURSDAY NIGHT FOR SLIGHTLY
WEAKER ONSHORE FLOW.

MODERATE TO STRONG ONSHORE FLOW WILL REDEVELOP FRIDAY NIGHT...JUST
AHEAD OF A WEAK COLD FRONT APPROACHING THE AREA. THE FRONT WILL MOVE
INLAND LATE FRIDAY NIGHT OR SATURDAY MORNING. BEHIND THE FRONT...A
WEAK SURFACE RIDGE WILL BUILD ALONG THE COAST THIS WEEKEND. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...GALE WARNING UNTIL 5 AM PDT WEDNESDAY FOR CENTRAL U.S. WATERS
     STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S. WATERS STRAIT OF
     JUAN DE FUCA.

     SMALL CRAFT ADVISORY UNTIL 3 AM PDT WEDNESDAY FOR ADMIRALTY
     INLET.


&&

$$

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