000
FXUS66 KSEW 032357
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 PM PST WED DEC 3 2008
.SYNOPSIS...A STRONG UPPER LEVEL RIDGE WILL KEEP WESTERN WASHINGTON
DRY THROUGH FRIDAY. THE RIDGE WILL BEGIN TO BREAK DOWN FRIDAY NIGHT
AS A WARM FRONT APPROACHES FROM THE NORTH. RAIN WILL MOVE INLAND AT
ON SATURDAY. THE ASSOCIATED COLD FRONT WILL SWING THROUGH WESTERN
WASHINGTON SUNDAY. A STRONGER PACIFIC FRONTAL SYSTEM WILL AFFECT THE
AREA LATE MONDAY INTO TUESDAY.
.SHORT TERM...BIG UPPER LEVEL RIDGE OF HIGH PRES IS LOCATED OVER 140
W. AFTER STRATUS LAYER BROKE UP THIS MORNING...MID AND HIGH
LEVEL CLOUDS FLOATED DOWN IN THE NORTHWEST FLOW ALOFT. A CUTOFF LOW
IS SINKING FURTHER SOUTH TOWARD THE CALIFORNIA COASTLINE. SURFACE
HIGH PRES OVER NORTHERN BRITISH COLUMBIA IS PRODUCING SOME LIGHT
OUTFLOW THROUGH THE FRASER RIVER VALLEY. THESE WINDS WILL PICK UP
SLIGHTLY TONIGHT AS THE BLI-YWL GRADIENT INCREASES...AND WILL LIKELY
HELP INHIBIT FOG FORMATION NORTH OF THE SAN JUANS. RIGHT NOW
DEWPOINTS RANGE FROM +7C AROUND CHEHALIS TO -2C AT BELLINGHAM.
SHELTERED LOCATIONS FROM THE BREEZY NORTHERLY OFFSHORE FLOW WILL
HAVE A CHANCE TO DROP TO NEAR FREEZING TONIGHT.
AFTER SOME MORNING FOG...MOST LIKELY IN THE SOUTH...THURSDAY WILL BE
A MOSTLY SUNNY DAY. THE NEXT SYSTEM WILL START TO FLATTEN THE RIDGE
THURSDAY NIGHT AND CLOUD COVER WILL INCREASE ON FRIDAY IN ADVANCE OF
A WARM FRONT. THE GFS HAS SLOWED UP SOUTHWARD PROGRESSION OF THE
RAIN SIMILAR TO THE EURO FOR SATURDAY. IF TREND CONTINUES...MOST OF
SATURDAY MAY END UP BEING DRY. DAMICO
.LONG TERM...GOOD AGREEMENT ON A DECENT TROUGH SWINGING DOWN FROM
THE NORTHWEST ON SUNDAY...LOWERING SNOW LEVELS AND PROVIDING A BRIEF
WINDOW FOR SOME MOUNTAIN SNOW LATE SUNDAY INTO MONDAY. A BRIEF BREAK
IN THE WEATHER WILL BE FOLLOWED BY STRONG WARM ADVECTION TUESDAY
AHEAD OF THE NEXT SYSTEM. SOUTHERLY GRADIENTS MAY PRODUCE BREEZY
GRADIENTS IN THE WARM SECTOR TUESDAY...HOWEVER THERE IS POOR
AGREEMENT BETWEEN THE EURO AND LATEST RUN OF THE GFS. DAMICO
&&
.AVIATION...AN UPPER RIDGE OFFSHORE WILL PROVIDE THE REGION WITH NLY
FLOW ALOFT. LOW LEVEL OFFSHORE FLOW. MEANWHILE...CLOUDS LINGERING
OVER THE AREA EARLY THIS EVENING WILL DISSIPATE ACROSS MUCH OF THE
AREA BY 06Z. HOWEVER CLEARING SKIES WILL RESULT IN FOG DEVELOPMENT
IN THE SHELTERED AREAS...SUCH AS KOLM...AFTER 03Z. EXPECT VSBYS/CIGS
TO DROP LOCALLY BELOW 3/4SM/300 FT BETWEEN KTCM AND KTDO AFTER 09Z.
KSEA...THE OFFSHORE OR NELY PRES GRADIENT WILL TIGHTEN SOME
OVERNIGHT AND WILL MAKE FOR A TRICKY FORECAST. THE FORECAST PROBLEM
WILL BE FOG...THAT IS WHETHER IT WILL DEVELOP AND IF SO HOW MUCH IT
WILL IMPACT OPERATIONS. HAVE BACKED OFF ON THE IDEA OF FOG FOR LATER
TONIGHT AND INCREASED WINDS A BIT. HOWEVER NOT CONFIDENT THAT THERE
WILL BE NO FOG AT THE AIRPORT...THUS INCLUDED A MENTION OF PATCHY
FOG AFTER 09Z.
&&
.MARINE...AN ELONGATED AREA OF LOW PRES ALONG THE WASHINGTON COAST
AND HIGHER PRES E OF THE CASCADES WILL RESULT IN OFFSHORE FLOW
THROUGH THU MORNING. THE OFFSHORE FLOW WILL WEAKEN THU AFTERNOON AND
THEN BECOME SOUTHERLY ON FRI AS A WARM FRONT MOVES ACROSS BRITISH
COLUMBIA. EXPECT INCREASED ONSHORE FLOW ON SATURDAY BEHIND A COLD
FRONT.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY IN EFFECT FOR THE WEST ENTRANCE TO THE
STRAIT OF JUAN DE FUCA.
$$
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