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fxus66 ksew 031735 
afdsew 


Area forecast discussion 
National Weather Service Seattle Washington 
by National Weather Service Portland Oregon 
930 am PST Wednesday Dec 3 2008 


Synopsis...a strong upper level ridge will keep western Washington 
dry through Friday. The ridge may begin to break down Friday night 
as a warm front approaches from the north. The associated cold front 
will swing through western Washington over the weekend. A stronger 
Pacific frontal system will affect the area Monday into Tuesday. 
&& 


Short term...not much activity showing up on the National Weather 
Service Doppler radar or on surface observations at this point this 
morning...though still pretty solid cloud cover. Weak surface low 
that had been off the Vancouver Island and western Washington coast 
and producing onshore flow is weakening and may yet see the lower 
clouds break up some later this afternoon and evening. There is an 
upper short wave along the b.C. Border that is spreading middle and 
high clouds over the area and that will move through today. This may 
limit what sunshine otherwise could filter through any breaks in the 
lower clouds. 


Behind this weak upper system a surface high sags south from Canada 
into eastern Washington late today and tonight...turning the low 
level flow offshore as the upper ridge over the northeast Pacific 
reasserts itself. Will likely see some areas of fog later tonight 
and Thursday morning in typically prone inland areas due to strong 
radiational cooling. 


Dry spell continues Thursday into Friday as the strong upper level 
ridge remains dominant over the Pacific northwest. Freezing levels will rise up 
and over 9000 feet with sunny skies expected on Thursday. As mentioned 
before...main weather concern is typical patchy late night and 
morning fog in The Lowlands with strong radiational cooling. Temperatures 
will also be cooler than recent nights with lows down to the upper 
20s and middle 30s. Pt 


Long term...no change. Timing of the next frontal system still 
remains unclear as a Rex block pattern develops with a cutoff low 
forming off the California coast. It is possible that a warm front 
will slide southeast through b.C. On Friday which may reach West Washington Friday 
night...thus flattening out the ridge and bringing rain back to the 
region. However...the European model (ecmwf) continue to show the ridge in tact with 
dry weather resuming across the state. Thus confidence remains low 
at this point and will keep probability of precipitation under climatology for now. Unsettled 
weather is possible through the remained of the weekend as a cold 
front and trailing upper level trough travel trough the area. 
Although again exact timing is a bit off between the Euro and the 
GFS. What is surprising though is both models show remarkable 
agreement in the far extended as a stronger system affects the area 
Monday night into Tuesday. Will need to watch this system as it evolves as 
models hint at heavier precipitation in the mountains with increasing 
southerly winds at the surface. 33 
&& 


Aviation...mixture of cloud decks this morning in weakening onshore 
flow with an MVFR deck along the coast...a VFR deck around 4000 feet 
elsewhere...except MVFR south sound and southwest interior and local 
IFR ceilings around kfhr. Ceilings will likely turn to mostly VFR late 
afternoon and evening. Light onshore flow weakening today and will 
turn offshore tonight. This will allow good radiational conditions 
tonight with areas of IFR developing mainly inland...and especially 
after midnight and in more sheltered areas. Expect better afternoon 
clearing on Thursday afternoon. By weather forecast office mfr/pqr 


Ksea...light wind...then NE 4-6 knots after 19z. Ceilings have been 
remaining MVFR and will continue that...delaying lift to VFR until 
later in the afternoon and evening. There is a risk of IFR 
conditions late tonight and Thursday morning. By weather forecast office mfr/pqr 
&& 


Marine...seas below 10 feet through tonight. Offshore gradients 
become strong enough tonight that small craft winds will be possible 
near the West Entrance to the Strait. Gradients slacken on Thursday with 
winds easing. Gradients may increase enough with the system this 
weekend for areas of Small Craft Advisory winds. Jw/dtm 
&& 


Sew watches/warnings/advisories... 
Washington...none. 
Pz...none. 


$$ 


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