Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 091714 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 914 AM PST Sat Dec 9 2017 .SYNOPSIS...A strong upper ridge will maintain dry and stagnant conditions across Western Washington through most of next week. The ridge looks like it will break down late in the week with the first chance of rain in over 10 days next Friday. High clouds could increase this weekend as a frontal system passes by well to the north. Air quality will likely worsen through the weekend. && .SHORT TERM...
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A strong upper level ridge over the Pac NW continues to bring dry and stable conditions to Western Washington. The main forecast challenge over the next few days will be fog coverage and temperatures. The visible satellite shows fog mainly over Puget Sound and the Strait of Juan de Fuca this morning. Temperatures will again vary widely depending on the fog coverage and thickness. Areas in the sun will see highs in the 40s today with 50s again at the coast. It`s sunny and mild up in the mountains, above the inversion. Expect similar conditions on Sunday. The dry conditions, light winds and poor mixing has lead to stagnant conditions. This may result in deteriorating air quality. An Air Stagnation Advisory remains in effect for the interior lowlands - burn bans are possible. There`s a slight change in the pattern on Monday when a shortwave trough clips the NW portion of the ridge, flattening heights over W WA. This features is dry but we could see a bit more mixing with a weaker low level inversion. 33 .LONG TERM...Previous discussion...Made a small change to the forecast this morning and added a chance of rain to the forecast on Friday. While the models differ on the timing there is general agreement that the ridge will weaken late in the week with an upper level trough arriving Friday or Saturday. This would end the dry streak at 11 days if the rain arrives on Friday. The longest dry streak in Seattle in December since the 3 weeks of dry weather from December 8-28 in 1985. For Tuesday through Thursday the upper level ridge axis shifts back over Western Washington with light flow in the lower levels keeping the possibility of the Air Stagnation advisory getting extended into at least the middle of next week. Felton
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&& .AVIATION...
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A strong upper level ridge will remain over the region for contd w or sw flow aloft. The low level flow will remain ely or offshore. Areas of LIFR CIGs/VSBYs over the interior lowlands will become patchy this afternoon. Expect the LIFR CIGs/VSBYs to become more widespread tonight. KSEA...The dense fog will lift this afternoon. However, fog will likely redevelop later this evening and then become dense again Sunday morning. Conditions will improve Sunday afternoon. Winds will be light and variable.
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&& .MARINE...
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Easterly or offshore flow will continue this weekend due to a 1040 mb high over eastern WA and lower pressure offshore. The flow will begin to weaken on Monday.
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&& .HYDROLOGY...River flooding is not expected for the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... 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 Sunday 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. Small Craft Advisory until 3 PM PST this afternoon for Coastal Waters From James Island To Point Grenville Out 10 Nm- Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. && $$ www.weather.gov/seattle

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