608 
fxus66 ksew 091737 cca 
afdsew 


Area forecast discussion 
National Weather Service Seattle Washington 
925 am PST Friday Jan 9 2009 


Synopsis...a moist frontal system will move through western 
Washington Saturday. High pressure will start to build into the 
region Sunday...but weak weather systems may keep light rain over 
western Washington at times through Monday. Strong high pressure 
builds by the middle of next week. 


&& 


Short term...dry today...just a chance of rain north part. The next 
frontal system will bring rain to western Washington Sat and Sat night...the 
wrfgfs shows a couple of inches of rain in the mountains...maybe 
2-3" out on the coast in the 24hrs ending 12z Sunday. The system 
looks moist on satimg west/ the moisture extending southwest to around 
30n/160w but this will be a far cry from what we just endured and 
the European model (ecmwf) is not very wet...with less than an inch of rain for the 
mountains through 12z sun. The freezing level will again rise but the 
first part of the precipitation will be snow in the Cascades. NAM gives 
Cascades a half inch to 1.5" of water but 850mb temperature stays below 0c 
until about 10pm Sat in the north Cascades. Temperatures in the central and 
southern Cascades warm to around +3c but precipitation amounts are lower there. 
Bottom line is that this gives just a fraction of what the mountains 
received the past few days. In the wetter NAM solution there is rain a 
times sun and Monday as systems drag through the area through the top of a 
dirty ridge...just the tail end of each system brushes through western Washington 
having dropped most of their precipitation in b.C. First. Probability of precipitation and qps do 
look a notch low. The global models do not play up the additional 
systems after the frontal system on Saturday...GFS and European model (ecmwf) are merely 
drippy through Monday...a little light rain at times...drizzly in The 
Lowlands. The upper heights are a little lower/the ridge is dirtiest 
in the NAM...by 00z Tuesday at 500mb the height over Seattle is 576dam 
on the GFS while the NAM is maybe 100m lower. Not sure whether the 
sloppier NAM with more onshore flow through Monday might is the best 
way to go with the forecast but Saturday certainly looks like a rainy 
day. 19 


Long term...after a couple of weak systems/dirty ridge scenario sun 
and Monday the ridge amplifies along 130w so that by the middle of next 
week should give the pacnw ample protection from any weather 
systems. A trend to a sunny forecast looks good as strong surface high 
pressure drops into Montana and the Dakotas and offshore flow is in 
place over western Washington. Off the GFS...there is about a 20mb difference 
between lower pressure along the Oregon coast and high pressure over NE Washington by 
midweek...and with 1000-500mb thickness rising into the 550's that 
ought give very fine weather for this time of year. It may take a 
few days to set up the dry weather pattern...but the GFS and European model (ecmwf) 
are a good match next Wednesday. 19 


&& 


Aviation...west-northwest flow aloft with flat upper ridge located inside of 
140w. Next system riding over the top of the ridge will impact 
southern British Columbia tonight. Rain may begin in the late 
afternoon around 00z for Bellingham and areas northward. Another 
wave will arrive offshore around 12z...and drop further south 
bringing rain to the entire area on Saturday. For the central Puget Sound 
sound and southward...mostly middle and high cloud will dominate 
through 12z Saturday...but ceilings will lower sharply toward 18z with 
MVFR ceilings likely to develop. Could still see fog for sheltered 
locations tonight like kolm. 


Ksea...scattered sct035-040 floating around the south sound this 
morning...but only really have to contend with middle and high level 
moisture through 12z Saturday. Damico 


&& 


Marine...combined seas have dropped off in the morning hours...with 
most nearby coastal locations reporting between 10 and 11 feet and 
expect seas to stay around this level for most of the day. With a 
frontal system passing to the north...surface winds have become more 
southeasterly north of Everett. Some guidance continues to suggest 
small craft winds for the northern inland waters...East 
Entrance...and Admiralty Inlet as early as 03z this evening. May end 
up hoisting a small craft for these areas with the afternoon 
package. Damico 


&& 


Sew watches/warnings/advisories... 
Washington...various flood warnings in effect for western Washington. 
Pz...Small Craft Advisory coast and West Entrance to the Strait. 
.Small Craft Advisory for rough bar conditions Grays Harbor bar. 


$$ 


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