000
FXUS66 KSEW 111608
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
900 AM PDT SAT OCT 11 2008
.SYNOPSIS...A STRONG UPPER RIDGE OFFSHORE WILL MAKE ITS WAY TOWARD
WESTERN WASHINGTON THIS WEEKEND PROVIDING DRY WEATHER WITH CRISP
MORNINGS AND PATCHY FOG. THE RIDGE WILL MOVE INLAND SUNDAY NIGHT...
ALLOWING A WEAK PACIFIC FRONTAL SYSTEM TO MOVE THROUGH THE AREA
MONDAY AND MONDAY NIGHT. WESTERLY FLOW ALOFT WILL BRING ANOTHER WEAK
FRONTAL SYSTEM INTO THE REGION LATER IN THE WEEK.
&&
.SHORT TERM...DRY NORTHERLY FLOW ALOFT CONTINUES OVER THE FORECAST
AREA COURTESY OF THE HIGH AMPLITUDE UPPER RIDGE THAT EXTENDS FROM
THE OFFSHORE WATERS INTO BRITISH COLUMBIA. SURFACE HIGH PRESSURE
OVER SOUTHERN BRITISH COLUMBIA IS PRODUCING WEAK NORTHERLY OFFSHORE
FLOW AT LOW LEVELS. CLEAR SKIES AND LIGHTER WINDS ALLOWED PATCHY TO
FOG TO DEVELOP AS MOST AREAS DROPPED INTO THE 30S OVERNIGHT AND SOME
AREAS -- INCLUDING BREMERTON...SHELTON...BELLINGHAM...ARLINGTON...
OLYMPIA...AND FORKS -- DIPPED INTO THE UPPER 20S. THE AIR MASS IS
MODERATING THOUGH WITH THE FREEZING LEVEL AT QUILLAYUTE MEASURED AT
6500 FT THIS MORNING.
CLEAR SKIES WILL BE THE RULE TODAY ONCE THE FOG DISSIPATES OVER THE
NEXT COUPLE HOURS...AND HIGH TEMPERATURES WILL AGAIN BE IN THE MID
50S TO LOWER 60S. THE UPPER RIDGE WILL KEEP WESTERN WASHINGTON DRY
TONIGHT AND SUNDAY AS IT CONTINUES TO MOVE SLOWLY EASTWARD. HIGH
CLOUDS ALONG THE LEADING EDGE OF THE FRONTAL SYSTEM IMMEDIATELY
UPSTREAM OF THE RIDGE WILL BEGIN SPREADING OVER THE AREA TONIGHT
THOUGH. THE EXTENT OF THESE CLOUDS WILL DETERMINE WHETHER TONIGHT IS
A REPLAY OF LAST NIGHT WITH AREAS BELOW FREEZING AND THE NEED FOR A
FROST ADVISORY. FOR NOW THE CURRENT FORECAST LOOKS GOOD...AND ANY
ADJUSTMENTS WILL BE A DECISION FOR THE AFTERNOON PACKAGE.
THE MODELS REMAIN CONSISTENT AND IN BROAD AGREEMENT THAT THE UPPER
RIDGE WILL PROGRESS THROUGH WESTERN WASHINGTON SUNDAY NIGHT AND
ACROSS EASTERN WASHINGTON INTO WESTERN MONTANA ON MONDAY. THE WEAK
WARM FRONT OF THE SYSTEM UPSTREAM WILL BRUSH THE AREA SUNDAY NIGHT
BRINGING A CHANCE OF RAIN TO THE COAST AND OLYMPICS. THE COLD FRONT
WILL MOVE THROUGH MONDAY AND MONDAY NIGHT WITH CHANCE TO LIKELY POPS
ACROSS THE ENTIRE FORECAST AREA. MCDONNAL
.LONG TERM...HERE IS THE LONG TERM SECTION FROM THE EARLY MORNING
ISSUANCE OF THE FORECAST DISCUSSION -- THE UPPER FLOW WILL GENERALLY
BECOME ZONAL DURING THE TUE-FRI PERIOD. BUT BOTH THE GFS ENSEMBLES
AND THE ECMWF ARE GENERALLY SHOWING DRY CONDITIONS WED AS SURFACE
HIGH PRES MOVES ACROSS B.C. LATEST GUIDANCE ALSO SHOWS WED NIGHT AND
THU BEING DRY OVER THE AREA...BUT CONFIDENCE IN THE FORECAST FALLS
OFF AFTER WED AS MODEL SOLUTIONS BEGIN DIVERGING SOMEWHAT. AT THIS
POINT WILL LIMIT CHANGES TO THE EXTENDED FORECAST TO DRYING OF THE
WED PERIOD. LATER SHIFTS MAY BE ABLE TO DRY THU OUT AS WELL IF THE
NEXT SET OF SOLUTIONS CONTINUE WITH THE DRYING TREND. ALBRECHT
&&
.AVIATION...UPPER RIDGE OFFSHORE WITH DRY NORTHERLY FLOW ALOFT OVER
WA. SURFACE HIGH PRES IN SOUTHERN BC WITH LIGHT OFFSHORE FLOW ACROSS
WA. AIR MASS DRY AND STABLE.
MAIN CONCERN THIS MORNING WAS FOG FORMATION IN PARTS OF WESTERN WA.
FOG WAS LIMITED TO THE SOUTH SOUND..LOWER CHEHALIS VALLEY..NEAR LAKE
WASHINGTON AND SNOHOMISH/SNOQUALMIE VALLEYS AS WELL AS COWLITZ
VALLEY.
THE REMAINING FOG SHOULD DISSIPATE BY 19Z REVEALING CLEAR SKIES.
HOWEVER..WILL HAVE SOME HIGH CLOUDS SPILLING OVER THE UPPER RIDGE
DRIFT ACROSS THE AREA TODAY. WITH SOME HIGHER CLOUDS TONIGHT..FOG
FORMATION WILL BE LIMITED AGAIN ON SUN MORNING.
KSEA...FOG MISSED THE TERMINAL THIS MORNING. SO EITHER CLEAR SKIES
OR SOME HIGH CLOUDS DRIFTING BY FOR TODAY AND TONIGHT. LIGHT WIND
EXCEPT NLY 5-9 KT THIS AFTERNOON AND EVENING. BUEHNER
&&
.MARINE...LIGHT OFFSHORE FLOW WILL CONTINUE ACROSS WESTERN WA TODAY
WITH A 1033 MB HIGH OVER SOUTHERN BC. THE HIGH WILL DRIFT E TONIGHT
AND SUN FOR LIGHT WINDS LATER TONIGHT AND SUN. A WEAK WARM FRONT
WILL APPROACH THE COAST SUN NIGHT AND MON. THEN THE ASSOCIATED COLD
FRONT WILL MOVE THROUGH THE AREA BY TUE..BRINGING ONSHORE FLOW AND
BUILDING COASTAL WATER SWELLS TO NEAR 10 FT. BUEHNER
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.
$$
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