Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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599 FXUS66 KSEW 190944 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 245 AM PDT Mon Mar 19 2018 .SYNOPSIS...Today will be partly to mostly sunny, with isolated showers in the mountains. A weak ridge over the region Tuesday will bring a mostly sunny day. Rain will return Wednesday and Thursday as a system moves through, with cool showery weather Friday into the weekend. && .SHORT TERM...Showers have dissipated and radar only shows isolated showers off the coast. An upper low off the Oregon coast will move farther away today, so any shower activity should be minimal. Models show a few showers in the mountains so have kept slight chance pops there. Skies will be partly to mostly sunny after patchy morning for. Highs today will be in the low to mid 50s. Tuesday will also be mostly dry. Skies will be mostly sunny, except northern sections could see some clouds from a weak system in southern British Columbia. Have also included some slight chance pops in the afternoon for the north Cascades, Olympics, and north coast. Highs Tuesday will be a few degrees warmer than today. A significant change in the pattern will occur around Wednesday. An approaching trough will turn the upper flow southerly, and moisture will advect into the area. Rain will develop on Wednesday, in the mountains at first, then spreading to all areas by Wednesday night. Skies will be mostly cloudy, but warm advection will allow highs to reach the mid to upper 50s. Burke .LONG TERM...Models have recently backed off on the strength of the surface gradient over the region as a surface trough moves toward the coast on Thursday. Now it appears conditions will be no more than breezy. Rain will continue at times on Thursday. The upper trough following the frontal system will bring cool showery weather to the area Friday through Saturday. The snow level will fall to around 1000 ft, so precipitation could fall as snow over the higher lowland areas. Despite being past the equinox on Wednesday, this is a wintry pattern. Highs will be mostly in the 40s, and snow will fall in the mountains. The upper trough will move off to the east on Sunday, for decreasing showers and more sun breaks. Burke && .AVIATION...Light east to northeast flow aloft over western Washington today as an upper level trough remains over the Oregon offshore waters. The air mass will continue to dry and stabilize today with the flow aloft becoming light northerly tonight as the trough shifts inland and a broad upper ridge centered well offshore noses into British Columbia. Except for some patchy late night and morning valley fog, VFR conditions are expected into Tuesday. KSEA...Expecting VFR conditions through the forecast period today and tonight. With some easterly flow aloft, may see some stratocumulus drift off the Cascades later today for some periods of BKN050-060 mainly during the midday and afternoon hours. Light and variable wind becoming northerly less than 8 knots late this afternoon and evening. 27 && .MARINE...Light onshore flow through Tuesday. A developing frontal system will slowly move into the coastal waters Wednesday. The front will push through the inland waters Wednesday night or early Thursday. At least small craft strength winds area expected in most waters. There is a chance of stronger surface low development which could produce stronger winds over portions of the waters Thursday, possibly near gale force coast and east entrance to the Strait. Confidence remains low on the strength of winds late Wednesday and Thursday, forecasts should be monitored. Weaker fronts will affect the waters Friday through the weekend. dtm && .HYDROLOGY...River flooding is not expected in the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.