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fxus66 ksew 282221 
afdsew 


Area forecast discussion 
National Weather Service Seattle Washington 
320 PM PDT Thursday Aug 28 2008 


Synopsis...the last few areas of light rain and drizzle will dry up 
this evening as the remnants of a frontal system dissipate over the 
region. A cold front will move through the region Friday afternoon 
and evening. A cool upper level trough will give scattered showers 
and fall like temperatures to the area Saturday and Saturday night. 
An upper level ridge will move over the region late Sunday through 
Labor Day. 


&& 


Short term...remaining areas of light rain or drizzle should end 
this evening. Still mostly cloudy across western Washington this 
afternoon...except clearing somewhat in the Lee of the Olympics so 
have partly cloudy some zones. Still areas of light rain over a good 
portion of the Cascades early this afternoon. Clouds are thicker on 
visible satimg along the coast with the remnants of the frontal 
system...some light rain or drizzle may persist around hqm where it 
rained a good part of the day today. The next system will increase the 
chance for rain again on Friday...becoming likely in the morning in 
the north and late afternoon south of Seattle. Rain changes to scattered 
showers behind the front Friday night. Under an upper trough scattered 
showers through Sat night. Have not put a chance of thunderstorms into the forecasts 
but it will be rather unstable Saturday afternoon. 19 




Long term...a flat upper ridge with heights near 573dam is over western 
Washington on Monday. Made no significant changes to the grids through the extended 
forecast and the models are not much different from previous runs just a 
bit flatter and more progressive looking. It isn't much of a ridge. 
In the past couple runs of the models the trough for Tuesday is weaker. 
And there is much more ridging toward the end of next week now in 
the GFS. The 12z GFS only takes 500mb heights down to 572dm 12z Tuesday 
and then builds an upper ridge centered along 130w with heights well 
into the 580s over western Washington by next Thursday...with the 588 contour 
over the coast Thursday night. The forecast has been difficult enough in the 
short term so I don't feel compelled to start pushing the grids all 
over in response to the more summery GFS for the latter half of next 
week. 19 




&& 


Aviation... 
moderately strong westerly flow aloft with weak embedded disturbances 
will continue overnight. The tail end of an upper trough will approach 
western Washington during the day Friday for for increased SW flow aloft. Expect a 
cold front to move across the area Friday afternoon...resulting in 
strengthening onshore flow. The air mass will remain moist but 
stable. 


Meanwhile...light rain or drizzle will continue over the mountains 
and portions of the coast through this evening. By 07z...the light 
rain/drizzle threat will become confined to the northern portion of the 
forecast area. Ceilings will be problematic but should generally be in 
the 1-3k feet range...lowest in the precipitation areas. There will also be 
some fog reducing visibilities to mainly in the 2-4sm range in those 
areas where precipitation has fallen...namely the Coast...Mountains...and 
far north. 


Ksea...predicting ceilings will remain a challenge. Ceilings should remain 
near 2500 feet but may briefly become scattered between 23z and 02z. 
Ceilings should lower to near 1500 feet after 12z. Southerly winds will continue 
but will gradually decrease. By 03z...speeds should be in the 6-10 
knots range. 


&& 


Marine... 
onshore flow will strengthen on Friday and then persist through this 
weekend. Expect the tail end of a cold front to move across the area 
on Friday. Gale force winds are expected to develop across the central 
and eastern Strait Friday afternoon. Westerly winds of 25 to 35 knots 
are anticipated...with speeds reaching 40 knots in the central 
Strait. Also expect a few gusts to near 45 knots Friday evening in the 
central and eastern Strait. 


&& 


Sew watches/warnings/advisories... 
Washington...none. 
Pz...Small Craft Advisory in effect for the Admiralty Inlet and 
Puget Sound sound/Hood Canal. 


Small Craft Advisory in effect for rough Grays Harbor bar 
conditions. 


Gale watch in effect for the central and eastern Strait of Juan 
Delaware fuca for Friday afternoon through late Friday night. 


$$ 


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