Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 081744 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 944 AM PST Fri Dec 8 2017 .SYNOPSIS...A strong upper ridge will maintain dry and stagnant conditions across Western Washington through the end of next week. Inversions will keep temperatures cooler in the lowlands and warmer temperatures in most mountain locations. Fog and Freezing fog will expand in coverage and duration today and Saturday. High clouds could increase this weekend as a frontal system passes by well to the north with less fog coverage Sunday into next weekend. Air quality will likely worsen over at least the next couple days. && .SHORT TERM...
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Little change in the overall weather pattern through this weekend. Strong high pressure over the Pac NW is the dominant feature, keeping the region dry through the period. Light winds and poor mixing is resulting in stagnant conditions which may lead to deteriorating air quality, possible reaching unhealthy levels. In coordination with local clean air agencies and WA Department of Ecology, an Air Stagnation Advisory was issued for the interior lowlands - burn bans are possible. Otherwise, forecast challenges will be fog coverage and temperatures in the interior. Still looking sunny and mild in the mountains. 33 .LONG TERM...Previous discussion...Differences have developed between the GFS and ECWMF regarding the strength of the ridge next week. The new GFS now more closely mirrors the ECMWF in tracking a weak upper low just off the coast around late Monday. This could induce some onshore flow or it may not have any surface reflection in the form of a front or stronger flow to break up inversions. Stuck with the inherited forecast and kept dry weather in the forecast for the next 7 day. There are some hints by models that a gradual weakening of the ridge could allow for a pattern change beyond day 7, beyond the forecast period. Mercer
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&& .AVIATION...
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A strong upper level ridge will remain over the region. Contd low level ely flow. Areas of fog (LIFR CIGs/VSBYs) over mainly the Puget Sound Region will dissipate this afternoon. Expect areas of fog (LIFR CIGs/VSBYs) to redevelop over the interior lowlands tonight. KSEA...Fog moved back in and was currently dense at the surface. The fog was very shallow, no more than 200 feet deep. The fog should begin lifting about midday; however, confidence in the timing was not high. If the fog dissipates this afternoon, expect it to redevelop tonight, probably earlier than last night.
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&& .MARINE...
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Lower pres offshore with high pres over the northern Great Basin will result in easterly flow through this weekend. The offshore flow will weaken on Monday.
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&& .HYDROLOGY...River flooding is not expected during the next week. && .SEW WATCHES/WARNINGS/ADVISORIES...
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WA...Air Stagnation Advisory until noon PST Monday 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...Small Craft Advisory until 3 AM PST Saturday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm- Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-West Entrance U.S. Waters Strait Of Juan De Fuca.
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&& $$ www.weather.gov/seattle

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