Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 181751 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 951 AM PST Sun Feb 18 2018 .SYNOPSIS...
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Cold and dry air from the interior of western Canada will spread across Western Washington this afternoon and evening, and a cold upper low will exit. This will help snow showers gradually taper off this afternoon. Look for dry, northerly flow aloft to become established over the area tonight and continue into Monday for cold and dry weather. A weak low pressure system will bring some light precipitation to the coast and Southwest Washington on Tuesday. A series of systems moving in from the northwest will keep chances of light precipitation going for the rest of the week.
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&& .SHORT TERM...
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The Bellingham-Williams Lake pressure gradient is currently near -15 mb, which is strong but not as strong as previously forecast. This is the gradient that correlates best to the strength of northeasterly Fraser Outflow. Dewpoints have really dropped in the northeast winds near Bellingham and the San Juans. The arrival of drier continental air over Northwest Washington will help snow showers to gradually taper off. The heaviest area of snow from Port Angeles east to near Arlington is showing signs of weakening now. The decreasing trend be an ongoing trend throughout the afternoon. The movement of a cold upper low over Southwest Washington will cause snow showers to end there last, i.e. late today. Most Winter Weather Advisories and Warnings will end at noon, except for 4 pm in the Southwest Interior. This looks like a good glidepath moving forward. A cold and dry air mass will be in place on Monday, with a widespread hard freeze both tonight and Monday night. The 00z ECMWF continues to show light precip spreading onto the coast and into Southwest Washington on Tuesday afternoon and evening. A larger minority of GFS ensemble members is now showing this is as well. Any light precip that spreads onshore late Tuesday will fall as snow over the lowlands. Haner .LONG TERM...A series of systems moving in from the northwest will keep chances of light precipitation going for the rest of the week, with a cool air mass supporting snow or a rain/snow mix over the lowlands when precip occurs. Haner
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&& .AVIATION...
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A low pressure center is near Grays Harbor this morning moving slowly southeast. There are scattered snow showers over the region and these will dry up and be pushed south over the course of the day as the dry northerly flow pushes south. Cold Fraser outflow will continue into tonight in the north. KSEA...Most of the snow shower activity around Puget Sound this morning seems to be closer to the Kitsap Peninsula and Hood Canal, but Seattle met yet get a skiff before the north wind dries the air up this afternoon.
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&& .MARINE...
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A modified arctic front will shift south through Western Washington today so north winds should develop over Puget Sound and be quite brisk through the afternoon. Fraser NE outflow gales are occurring in the north. A surface low is near the south Washington coast and that is moving into southwest Wa. Gradients will ease Monday.
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&& .HYDROLOGY...River flooding is not expected the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES...
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WA...Winter Weather Advisory until 4 PM PST this afternoon for Cascades of Pierce and Lewis Counties-East Puget Sound Lowlands-Southwest Interior. Wind Advisory until 10 PM PST this evening for San Juan County- Western Skagit County-Western Whatcom County. Winter Storm Warning until noon PST today for Everett and Vicinity-Olympics. Winter Weather Advisory until noon PST today for Admiralty Inlet Area-Central Coast-Eastern Strait of Juan de Fuca-Lower Chehalis Valley Area-North Coast-Western Skagit County- Western Strait of Juan De Fuca. High Surf Advisory until 2 PM PST this afternoon for Central Coast-North Coast. PZ...Small Craft Advisory for rough bar until 4 AM PST Monday for Grays Harbor Bar. Small Craft Advisory until 2 AM PST Monday for Admiralty Inlet- 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 James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-Puget Sound and Hood Canal-West Entrance U.S. Waters Strait Of Juan De Fuca. Gale Warning until 4 AM PST Monday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands.
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&& $$ www.weather.gov/seattle

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