Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 121642 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 845 AM PST Tue Dec 12 2017 .SYNOPSIS...
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A strong upper level ridge will maintain dry and stagnant conditions across most of Western Washington through Thursday afternoon. The ridge will break down on Thursday allowing a cold front to bring rain late Thursday night and Friday. Another frontal system will continue the wet weather pattern into the weekend.
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&& .SHORT TERM...
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Mid and high clouds cover Western Washington this morning. Winds are light but the cloud cover kept fog to a minimum. The clouds also kept temperatures several degrees higher than yesterday morning, with mostly 30s at 8 AM along with a few low 40s near the water. Satellite imagery shows a mass of clouds off the coast, so today will be mostly cloudy with highs 45-50. Guidance suggests clouds will not dissipate until after midnight, when the upper ridge sharpens a bit. As the clouds fade, and winds remain light, fog is likely to appear, especially around Puget Sound. Overnight lows will be mostly in the 30s. Wednesday and Thursday will be mostly sunny with areas of night and morning fog. Highs will be in the mid 40s to lower 50s, but low temperatures will fall into the mid 20s to mid 30s. An approaching front will spread clouds over the area Thursday night and eventually bring a little rain late Thursday night and Friday. With the upper level ridge in place and light flow at the lower levels through the short term, the air stagnation advisory will remain in effect through Thursday afternoon. Burke .LONG TERM...Previous discussion...Extended models in fairly good agreement during the extended period with the trend on the 00z run a little slower and weaker with the system over the weekend. Upper level trough moving through Western Washington on Friday behind the front. Even through the models are not as strong with the warm front as previous runs for Saturday will still keep at least chance pops in the forecast. Trailing cold front arrives on Sunday. Another upper level trough digs down off the Coast on Monday keeping a chance of precipitation in the forecast. Felton
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&& .AVIATION...
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An upper ridge will build over the area through tonight with light to moderate westerly flow aloft. The remnants of a dissipating frontal system over Western Washington is bringing mid and high level moisture to the area today. Expect the clouds to gradually decrease this afternoon and evening as surface high pressure builds to the east and northeast of the area. The combination of clearer skies and light offshore flow late tonight into Wednesday morning will result in an increasing low- level temperature inversion with moisture trapped near the surface. Expect areas of fog to develop late tonight in valleys with the fog becoming more widespread during the morning hours. Albrecht KSEA...The weak front that is breaking up near the coast probably wont have much in the way of cloudiness today.
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&& .MARINE...
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A ridge of high pressure extending from Southern British Columbia into Eastern Washington will give light offshore flow to the waters today through Thursday. A cold front will move east through the waters Thursday night into Friday morning. A warm front will approach the coastal waters on Saturday. Small craft advisory conditions are likely across most of the waters with these frontal systems. Albrecht
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&& .SEW WATCHES/WARNINGS/ADVISORIES... WA...Air Stagnation Advisory until 2 PM PST Thursday for Admiralty Inlet Area-Bellevue and Vicinity-Bremerton and Vicinity- East Puget Sound Lowlands-Eastern Strait of Juan de Fuca- Everett and Vicinity-Hood Canal Area-Seattle and Vicinity- Southwest Interior-Tacoma Area-Western Skagit County- Western Whatcom County. PZ...None. && $$ www.weather.gov/seattle

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