Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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350 FXUS66 KSEW 190418 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 817 PM PST Sun Feb 18 2018 .SYNOPSIS...
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Cold and dry conditions will persist as north and northeast winds remain over Western Washington. A widespread hard freeze is expected tonight through Tuesday night. A weak system dropping down offshore late Tuesday could bring a little snow to the coast and Southwest Washington. Other systems around Wednesday night, Friday, and next Sunday could bring more precipitation, with lowland snow possible with the Wednesday night and Friday systems.
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&& .SHORT TERM...
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Gradients continue to gradually ease this evening which will resulting wind speeds slowly relaxing. Current obs around the CWA continue to show gusts around the area...the strongest being at any sites near water...but the vast majority fall below any headline criteria. The exception to this...Western Whatcom county and the San Juans...with their current High Wind Warning in place...looks to have fallen below that criteria. As such...will monitor next set of obs before making a decision whether or not to downgrade to a wind advisory or just scuttle the headline altogether. Regardless of speed...these winds are responsible for bringing a cold and dry continental air mass into the region. In fact...likely to be the coldest air mass of this winter and this will remain in place at least through Monday night. A widespread hard freeze is forecast tonight, Monday night, and possibly Tuesday night. Lows in the low-mid 20s will be common over the next two nights. Sunny skies forecast during the day on Monday. Late Tuesday, the ECMWF is consistent with its previous solutions in dropping a system southward off the coast and slopping some precipitation onto the coast and into Southwest Washington. A growing minority of GFS ensemble members bring a few hundredths of precip to Hoquiam late Tuesday as well, and the 18z NAM brings precip to within 25 miles of the coast. If precip moves onshore, the air mass will still be cold enough for snow to sea level. Have about 20-40 percent PoPs late Tuesday for the coast and SW Wa, but have a dry forecast from Seattle metro on north. This system should exit southward early Wed, with a mainly dry but cool day expected. Temperatures on Wed will still be well below normal. Models agree in dropping another shortwave down along the southeast Alaska and B.C. coasts and into Western Washington Wed night and early Thu. The NAM is perhaps most bullish with precip amounts in the warm advection pattern preceding the shortwave. The air mass will still be sufficiently cold for all snow, except perhaps at the immediate coast of Grays Harbor County. Possibilities over the lowlands range from non-impactful flurries to a few inches of snow. The NAM favors neither the coast nor inland, while the EC favors the coast. The latest GFS just has flurries. Ensembles point to a range of possibilities, most on the lighter side. Haner/SMR .LONG TERM...From Previous Discussion...A highly amplified longwave pattern will continue, with cold north-northwest flow aloft from Thursday through next weekend. Looks like additional systems dropping down in cold northwest flow aloft around Friday and next Sunday. The Friday system could see a transition from some snow to rain as warmer air spreads inland. Snow levels by next Sunday should rise above the lowlands, perhaps to 1000 to 1500 feet. Still, below normal temperatures. Haner
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&& .AVIATION...
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Northerly flow aloft will continue over W WA tonight and Monday. VFR conditions in place thanks to cold...dry air mass. Clear skies tonight will persist into Monday with some occasional SCT high clouds. Surface winds this evening will remain gusty as Fraser outflow slowly starts to subside with calmer winds expected in most locations by 12Z Monday morning. KSEA...Dry cold air and northerly winds as Fraser outflow continues tonight. Wind speeds gradually diminishing with gusts expected to end by early Monday morning. Skies should be mostly clear from here on out til weather systems arrive starting on Tuesday.
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&& .MARINE...
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Strong Fraser outflow winds still having impacts...particularly over the Northern Inland Waters. While most waters have fallen below gale...still isolated obs coming in from within Gale Warning zones...so will leave inherited headlines alone there. Remainder of waters look to be behaving...so not much expected in ways of updates for evening package. A series of weather systems will drop down out of the northwest Tue- Sat so there will probably be about three periods where fairly light southerly winds develop, and then a pretty decent push of NW winds behind each front comes through the region--especially later in the week when the systems seem be be successively stronger.
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&& .HYDROLOGY...River flooding is not expected the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES...
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WA...High Wind Warning until midnight PST tonight for San Juan County-Western Whatcom County. PZ...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-West Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory for rough bar until 4 AM PST Monday for Grays Harbor Bar. 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. Small Craft Advisory until 2 AM PST Monday for Puget Sound and Hood Canal. Gale Warning until 9 PM PST this evening for Puget Sound and Hood Canal.
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&& $$ www.weather.gov/seattle

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