Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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FXUS66 KSEW 030342
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
842 PM PDT SUN AUG 2 2015

.SYNOPSIS...AN UPPER TROUGH WILL BE OVER THE AREA MOST OF THE
COMING WEEK WITH LOW LEVEL ONSHORE FLOW.

&&

.SHORT TERM...LOW LEVEL ONSHORE FLOW WILL INCREASE OVER THE FEW
DAYS AS AN UPPER TROUGH MOVES OVER THE PACIFIC NORTHWEST. THIS
WILL COOL HIGHS BACK TO NEAR NORMAL. IT WILL ALSO BRING AN
INCREASE IN NIGHT AND MORNING LOW CLOUDS BEGINNING MONDAY NIGHT.
IT LOOKS GENERALLY DRY THROUGH WEDNESDAY BUT AN ISOLATED
THUNDERSTORM CANNOT BE RULED OUT ON MONDAY NEAR THE CASCADE CREST
WHEN SOME ELEVATED CONVECTION COULD DRIFT UP FROM THE SOUTH IN
INCREASING SOUTHERLY FLOW ALOFT. SCHNEIDER

.LONG TERM...PREVIOUS DISCUSSION...HEIGHTS ACTUALLY START TO RISE
ON THURSDAY AS THE UPPER TROUGH IN BRITISH COLUMBIA MOVES WELL TO
THE EAST. ONSHORE SURFACE GRADIENTS ALSO WEAKEN. A WARMING TREND
SHOULD BEGIN WITH HIGHS BACK IN THE LOW TO MID 80S THURSDAY AND
FRIDAY AND GENERALLY DRY WEATHER EXCEPT FOR A CHANCE OF SHOWERS IN
THE MOUNTAINS THURSDAY.

THE TRANSIENT UPPER RIDGE RESPONSIBLE FOR WARM AND DRY WEATHER WILL
MOVE OUT OF THE AREA BY SATURDAY. BOTH THE GFS AND EURO SHOW LIGHT
PRECIPITATION OVER MOST OF THE AREA ON BOTH WEEKEND DAYS. HAVE
INTRODUCED A CHANCE OF SHOWERS TO THE WHOLE CWA ON BOTH SATURDAY AND
SUNDAY. HIGH TEMPERATURES WILL BE MAINLY IN THE 70S. BURKE

&&

.AVIATION...A BROAD UPPER LEVEL RIDGE WILL REMAIN OVER THE PACIFIC
NW THROUGH TONIGHT WITH LIGHT SOUTHWEST FLOW ALOFT. THE AIR MASS IS
DRY EXCEPT FOR HIGH LEVEL MOISTURE MOVING N FROM OREGON. MODERATE
ONSHORE FLOW WILL ALLOW SHALLOW STRATUS TO FORM ALONG THE COAST
TONIGHT...AND SPREAD INLAND THROUGH THE STRAIT OF JUAN DE FUCA AND
FROM KHQM OVER THE SW PART OF PUGET SOUND OVERNIGHT. IFR CONDITIONS
ARE EXPECTED TO DEVELOP UNDER THE STRATUS...BUT IT SHOULD DISSIPATE
BY 19Z. EXCEPT FOR THE STRATUS GOOD VFR CONDITIONS ARE EXPECTED TO
CONTINUE THROUGH MONDAY.

KSEA...GOOD VFR CONDITIONS WILL CONTINUE TONIGHT AND MONDAY. HIGH
CLOUDS OVER THE AREA TONIGHT WILL MOVE E MONDAY AFTERNOON. ONSHORE
FLOW IS EXPECTED TO SPREAD STRATUS OVER THE FAR SW PART OF PUGET
SOUND MONDAY MORNING...BUT THE STRATUS IS NOT EXPECTED TO REACH
KSEA. SURFACE WINDS WILL BE SOUTHERLY UP TO 5 KT THROUGH 06Z THEN
BECOME LIGHT AND VARIABLE THE REST OF TONIGHT. KAM

&&

.MARINE...HIGH PRESSURE WILL REMAIN OFFSHORE WITH LOW PRESSURE
EAST OF THE CASCADES THROUGH THIS WEEK. ONSHORE FLOW WILL
INCREASE MONDAY AND MONDAY NIGHT AND REMAIN FAIRLY STRONG THROUGH
MIDWEEK. SMALL CRAFT ADVISORY NORTHWEST WINDS WILL CONTINUE
OVER MOST OF THE COASTAL WATERS ZONES TONIGHT...AND THEN AGAIN AT
TIMES EARLY NEXT WEEK.

A GALE WARNING IS IN EFFECT FOR THE CENTRAL AND E STRAIT THIS
EVENING. THE UIL-BLI PRESSURE GRADIENT IS UP TO 2.1 MB...SLIGHTLY
HIGHER THAN LAST NIGHT. A BRIEF GALE IS STILL A DEFINITE POSSIBILITY
THIS EVENING. A SCA HAS BEEN ISSUED FOR CENTRAL/EAST STRAIT TO COVER
THE WEAKENING WINDS AFTER MIDNIGHT. THE GFS DOES NOT SHOW THE
PRESSURE GRADIENT WEAKENING QUITE AS MUCH OVERNIGHT AS PREVIOUS
NIGHTS...SO PER THE CANADIAN LAM MODEL THERE IS A CHANCE THAT LOW
END SCA LEVEL WINDS COULD CONTINUE IN THE STRAIT INTO MONDAY
MORNING.

A DRY COLD FRONT IS EXPECTED TO APPROACH W WA FROM THE NW ON
MONDAY...CROSSING THE AREA MONDAY EVENING. THE MAIN IMPACT WILL BE
TO STRONGLY INCREASE THE ONSHORE PRESSURE GRADIENT ON MONDAY AS IT
APPROACHES. THE STRONG ONSHORE FLOW SHOULD RESULT IN SOLID GALE
FORCE WESTERLIES IN THE CENTRAL AND EAST STRAIT LATE MONDAY
AFTERNOON AND MONDAY NIGHT. A GALE WATCH IS ALREADY IN EFFECT AND
WILL LIKELY BE UPGRADED TO A GALE WARNING IN THE EARLY MORNING
FORECAST. SCA WINDS ARE ALSO EXPECTED OVER PARTS OF THE COASTAL
WATERS MONDAY NIGHT.

MODERATE TO STRONG ONSHORE FLOW SHOULD CONTINUE TUESDAY NIGHT AND
WEDNESDAY NIGHT. SCA WINDS ARE HIGHLY LIKELY IN THE STRAIT AND GALES
ARE POSSIBLE. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 3 AM PDT MONDAY FOR COASTAL WATERS
     FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-COASTAL
     WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10 TO 60 NM-
     COASTAL WATERS FROM JAMES ISLAND TO POINT GRENVILLE OUT 10
     NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER
     10 TO 60 NM-COASTAL WATERS FROM POINT GRENVILLE TO CAPE
     SHOALWATER OUT 10 NM.

     GALE WATCH FROM MONDAY AFTERNOON THROUGH LATE MONDAY NIGHT FOR
     CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE
     U.S. WATERS STRAIT OF JUAN DE FUCA.

     SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 5 AM PDT MONDAY
     FOR CENTRAL U.S. WATERS STRAIT OF JUAN DE FUCA-EAST
     ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.

     GALE WARNING UNTIL MIDNIGHT PDT TONIGHT FOR CENTRAL U.S. WATERS
     STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S. WATERS STRAIT OF
     JUAN DE FUCA.

&&

$$

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