Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000 FXUS66 KSEW 242212 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 312 PM PDT Fri Mar 24 2023 .SYNOPSIS...
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A cool and marginally active weather pattern will remain over Western Washington through the weekend. Widely scattered showers, with a chance of thunder and possibly a Puget Sound Convergence zone Friday night will trend drier Saturday and Sunday. Mountain snow or snow showers will continue through the weekend. Colder temperatures will leave the door open for at a chance of a rain/snow mix for some locations during the late night and early morning hours Saturday and Sunday. Drier weather is in store early next week.
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&& .SHORT TERM /TONIGHT THROUGH MONDAY/...
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Scattered showers over the area this afternoon will continue into this evening. There remains a chance of isolated thunderstorms with this - especially along the coast and interior south of Puget Sound. Increasing onshore flow will elevate odds of the formation of a Puget Sound Convergence zone late this afternoon and evening. Have included a chance of thunder over Snohomish and King Counties this evening to reflect the possibility of seeing lightning with the convergence zone if it forms. In addition, both the HREF and UW HiRes ensemble systems continue to show the possibility of persistent or heavier showers in the convergence zone lowering the snow level - resulting in some snow mixed in with convergence zone rain tonight.While impacts aren`t expected, they remain possible and folks traveling should be aware of the possibility. Ensemble members that do develop a convergence zone show it developing late this afternoon/early evening - between the I-90 corridor in King County northward to US-2 in Snohomish County. In addition, the cooler air mass over the region through the weekend will help lower snow levels to below 1000 feet during the late night/early morning hours going into Saturday and again going into Sunday. This will allow for a broader potential for a rain/snow mix or even just snow showers at those times - very limited accumulations, if any at all, are possible. Sunday will trend drier but with the broad trough still over the region, showery weather will remain over the area - especially the higher terrain. Even so, as is typical for this time of year - even a few cloud breaks could boost high temps Sunday just north of 50 for many areas in the interior. Monday will see an upper level shortwave trough that has moved down the British Columbia Coast slide southward well to the west of Washington. This may provide some boost to clouds and even some light precipitation for Western Washington - but in general the idea is for another benign, mostly dry day Monday. .LONG TERM /TUESDAY THROUGH FRIDAY/...Ensembles from the ECMWF, GEFS and CMC systems consitstenly show the offshore upper level trough strengthening as it digs southwared over the Eastern Pacific before moving onshore somehwere over Southern Oregon into Northern California Monday into Tuesday. This also equates to the some degree of upper level ridging and drier weather building in over the Pacific Nortwest midweek. Some potential for offshore low level flow will help with less cloud cover high temperatures near normal - in the mid 50s. The pattern may weeken late in the week opening the door for a potential return of at least Spring showers toward the latter half of the week.
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&& .AVIATION...
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A broad upper level trough will remain centered over Western Washington into Saturday producing light flow aloft. The air mass is moist and somewhat unstable. Conditions will remain predominantly MVFR across the area in scattered showers with any improvements to VFR this evening likely to be brief. A convergence zone will persist in the vicinity of KAWO/KPAE into the evening hours. KSEA...MVFR ceilings will persist across the terminal with scattered showers. Any improvement to VFR late this afternoon/evening is likely to be brief. Surface winds southwesterly 10 to 15 knots...with higher gusts this afternoon. Winds will ease somewhat late this evening and remain S/SW 7 to 11 knots. 27
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&& .MARINE...
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Small craft advisories continue most waters with gales in the strait. High pressure building well offshore and lower pressure over the interior will continue to produce onshore flow into the weekend. The flow will then turn offshore early next week as a surface low digs southward over the offshore waters. Seas of 14 to 17 feet across the coastal waters today will remain elevated into Saturday before gradually subsiding back below 10 feet late in the weekend. 27
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&& .HYDROLOGY...No river flooding expected in the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Winter Weather Advisory until 5 AM PDT Saturday for West Slopes North Central Cascades and Passes-West Slopes South Central Cascades and Passes. PZ...Small Craft Advisory until 5 AM PDT Saturday 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-Grays Harbor Bar-West Entrance U.S. Waters Strait Of Juan De Fuca. Gale Warning until 7 PM PDT this evening for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory until 11 PM PDT this evening for Admiralty Inlet-Northern Inland Waters Including The San Juan Islands. && $$

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