Scientific Forecaster Discussion

000 fxus66 ksew 212332 afdsew Area forecast discussion National Weather Service Seattle Washington 332 PM PST Thu Feb 21 2019 Synopsis...dry northerly flow will continue tonight for quiet weather. A frontal system will arrive from the northwest on Friday with more snow in the mountains. A cool upper trough will follow the front for the weekend. Low snow levels will continue through the period. && Short term /tonight through Sunday/...we have sunny skies across the board today with temperatures into the lower to mid 40s. Quiet weather will continue tonight with increasing high clouds aloft. Lows will be mainly in the low to mid 30s. Moisture will spread inland on Friday as our next frontal system moves in. Timing is crucial as snow levels will remain low during the morning hours. Initially, we may see a rain/snow mix as the precip moves in. However, amounts look light and we are not expecting accumulating snowfall. Snow levels will rise in the afternoon for mainly rain in The Lowlands. Up in the mountains, the Cascades will see more snow including all passes. Models are showing a convergence zone aimed between Stevens and Snoqualmie Pass Friday night with a period of heavy snow possible. A Winter Weather Advisory will be issued for 4-9" of new snow through late Friday night. Saturday will be cool and showery as an upper level low spins over the region. Snow levels will remain low, only a few hundred feet during the overnight/morning hours, with a rain/snow mix possible over The Lowlands. Snow accumulations looks mainly light and spotty, if anything. Temperatures will reach the lower 40s during the afternoon to help minimize any impacts. Showers will be decreasing on Sunday as the low weakens. 33 Long term /Monday through Thursday/...models are trending drier for the Monday/Tuesday period as our next system tracks south of the County Warning Area. So even though snow levels will remain low, we are lacking the moisture and the threat for more lowland snow is decreasing. A wetter but warmer system may track north into western Washington Tuesday night or Wednesday with rising snow levels and rain. It looks like temperatures will continue to moderate as we move toward the end of next week. Back to normal? 33 && Aviation...moderate southwest flow aloft will develop ahead of a frontal system tonight. An upper trough and surface low will move into western Washington on Friday. VFR skies through most of tonight will lower into an MVFR deck as rain develops Friday morning. Rain will ease Friday evening but low clouds, possibly low MVFR will persist over the area. A rain/snow mix could occur at the onset Friday morning above a couple hundred feet, then rain is expected. A mix of rain and snow showers are expected Friday but accumulation will be minor or none at all. Ksea...northwest wind to 10 kt becoming southerly by midnight. VFR skies through most of tonight. High and mid-level clouds increase tonight and lower to MVFR toward 18z Friday as rain spreads into the area with the next frontal system. A rain/snow mix could occur at the onset and also with a system on Saturday, but little accumulation is expected. Surface winds north-NE 5 to 10 knots today shifting to southerly near or after 06z tonight. Dtm && Marine...offshore flow will continue to ease this evening and gradually shift to the southwest overnight as a low pressure system skirts down the coast of British Colombia. Westerly swell to 10 feet will continue to subside this evening. The frontal system will move onshore Friday morning. Small craft southerlies are anticipated along the coastal waters and areas along Puget Sound and the northern interior ahead of the frontal boundary. Small craft winds will shift to the northwest along the coastal waters and west along the Strait of Juan de Fuca in the fronts wake. Winds will gradually ease up into Saturday. Offshore flow will redevelop Sunday and continue into Monday as high pressure moves over British Columbia and low pressure approaches Oregon. Sb && Hydrology...river flooding is not expected for the next 7 days. && Sew watches/warnings/advisories... Washington...Winter Weather Advisory from noon Friday to 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 from 1 am to 5 PM PST Friday 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-East Entrance U.S. Waters Strait of Juan de Fuca-northern inland waters including the San Juan Islands-Puget Sound and Hood Canal-West Entrance U.S. Waters Strait of Juan de Fuca. Small Craft Advisory for hazardous seas until 8 PM PST this evening 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 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. Small Craft Advisory for rough bar until 8 PM PST this evening for Grays Harbor bar. Small Craft Advisory from 10 am to 5 PM PST Friday for central U.S. Waters Strait of Juan de Fuca.

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