Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 230613 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 1013 PM PST Fri Feb 22 2019 .SYNOPSIS...A cool upper level trough will move down over Western Washington tonight and remain over the area through the weekend. The trough will keep showers in the forecast with daytime highs remaining well below normal. A system moving up from the south may bring more lowland snow to the region late Sunday night and Monday. && .SHORT TERM /TODAY THROUGH MONDAY/...Satellite imagery shows mostly cloudy skies over Western Washington this evening. Doppler radar still has a convergence zone over most of Snohomish county at 9 pm/05z. Across the remainder of the area showers are scattered with the northwesterly flow aloft causing a rain shadow for the central and southern Puget Sound. Temperatures at 9 pm were in the mid 30s to lower 40s. Nothing new in the short term in the 00z model runs with a cool upper level trough remaining over the area tonight through the weekend. Snow levels will remain low, a 1000 feet or less, but showers will be scattered. The best chances for seeing snow in the lowlands will be on the higher hills in the late night and morning hours. Showers decreasing Saturday night into Sunday as the trough weakens over the region. Fraser river outflow winds beginning Saturday night but with the model peaking the Bellingham to Williams Lake gradient in the -15 to 18 mb range not expecting any advisory level winds for Whatcom county. Highs will remain well below normal, in the lower 40s for the most part. With a little clearing in the early morning hours some locations will drop below freezing. Most locations will end up in the upper 20s to mid 30s both Saturday and Sunday morning. The big forecast issue for the weekend will be the chances for lowland snow late Sunday night into Monday. The 00z models so far are of little help with the GFS solution keeping the precipitation south of the area while the NAM lifts the front far enough north Monday into Monday night with a few inches of snow over the Puget Sound and the potential for a significant snow event over the Southwest Interior. End of February? Will see what the 00z ECMWF has to say, but with the lack of consistency in the solutions a broad brush forecast will be the way to go until we get closer to the event. No changes to the forecast this evening. Snow showers have diminished in the Cascades but with a convergence zone and another batch of showers arriving in a couple of hours will keep the advisory up through the early morning hours. Felton .LONG TERM /TUESDAY THROUGH FRIDAY/...Showers will continue through the rest of the week as an upper level trough stalls offshore then shifts inland. Guidance shows we will remain a few degrees below normal through the period. Snow levels will be higher, mostly in the 1,000-2,000 ft range, for rain in the lowlands. We may see a break in the action toward the end of the week as a ridge builds in. 33 && .AVIATION...Northwesterly flow aloft becoming more westerly late Saturday as upper level trough settles into the area. Weak low level onshore flow will turn light offshore on Saturday. With the light onshore gradients ceilings overnight in the 1000-2500 foot range with higher ceilings over the northern portion of the area. Conditions not changing much through the morning hours. Improving trend Saturday afternoon with ceilings lifting up into the 4000-5000 foot range. KSEA...Ceilings in the 1000-1500 foot range into the morning hours. Some improvement late Saturday morning with ceilings lifting up to around 4000-5000 feet in the afternoon. Southerly winds 4 to 8 knots becoming southeasterly late Saturday. Felton && .MARINE...Winds continuing to ease overnight in the wake of Friday`s front. Still some small craft advisory westerlies in the central and Eastern Strait of Juan de Fuca. Small craft west northwesterly winds also over the outer coastal waters tonight. Low level flow turning weak offshore during the day Saturday into Sunday morning as a weak surface low offshore moves south to off the Oregon coast. Fraser river outflow winds developing Saturday night but will be confined to the Northern Inland Waters. Low level offshore flow will continue into Tuesday with high pressure over British Columbia and lower pressure to the south of Washington. Felton && .HYDROLOGY...River flooding is not expected for the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Winter Weather Advisory until 6 AM PST Saturday for Cascades of Pierce and Lewis Counties-Cascades of Snohomish and King Counties-Cascades of Whatcom and Skagit Counties. PZ...Small Craft Advisory for rough bar until 9 AM PST Saturday for Grays Harbor Bar. Small Craft Advisory until 4 AM PST Saturday for Central U.S. Waters Strait Of Juan De Fuca-Coastal Waters From Cape Flattery To James Island 10 To 60 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-East Entrance U.S. Waters Strait Of Juan De Fuca. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.