Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
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Issued by NWS Seattle/Tacoma, WA
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-- Discussion containing changed information from previous version are highlighted. --791 FXUS66 KSEW 202300 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 400 PM PDT Thu Mar 20 2025 .SYNOPSIS...-- Changed Discussion --Another system will move into the region tonight into Friday and will bring the next round of lowland rain, mountain snow, and breezy winds to the area. The pattern looks to remain active through the weekend, with several additional disturbances crossing the region. An atmospheric river will then likely reach the area for the start of next week, before a mild and drier pattern around Tuesday. Yet another system arrives Wednesday night.-- End Changed Discussion --&& .SHORT TERM /TONIGHT THROUGH SUNDAY/...-- Changed Discussion --The next weather system continues to move into the area this afternoon with widespread rain spreading across the Olympic Peninsula and into the Puget Sound region. Expect gusty winds to peak late this evening or overnight, before easing early Friday. The strongest winds with gusts around 40 mph are expected along the coast and near the water from around the eastern Strait of Juan de Fuca northward. Snow levels will briefly rise to around 3500 feet, before lowering again through the day on Friday. With this pattern, have elected to continue the winter storm warning for Stevens Pass northward and a winter weather advisory for Snoqualmie Pass southward. Expect around 1-2 feet of snow through Saturday across the north and up to around a foot for the south (with slightly lower amounts at Snoqualmie Pass due to periods of rain due to the snow levels rising as mentioned above). With the system moving east, expect a transition to showers across much of the area on Friday afternoon. An isolated thunderstorm is possible in the strongest showers, with around a 15% chance of development. A convergence zone is also likely to develop Friday evening and provide the focus for additional steadier lowland rain and mountain snow. A weak upper ridge begins to build on Saturday with the lingering showers being increasingly confined to the mountains. Not much change in the temperatures for the lowlands through the next couple of days with daytime highs in the 50s and overnight lows around 40. As the ridge builds over the western U.S. into Sunday, there remains some notable spread in the ensemble guidance for the placement of a moderately strong atmospheric river. Latest cluster analysis continues to suggest this plume of moisture will impact the region at some point Sunday. That said, there is a large spread in the likely rainfall amounts and this will be a factor in the potential for any river flooding. See the hydrology section for more details. With the very warm air mass moving into the area, expect to see snow levels quickly climb above 7000 ft by late Sunday and closer to 8000 ft into Monday. .LONG TERM /MONDAY THROUGH THURSDAY/...Expect high snow levels and lingering showers into Monday morning, but the ridge of high pressure builds further into the region. This will effectively cut off the influx of moisture into the region but also continue to support a warming trend. Temperatures likely to reach well above normal Tuesday and into Wednesday, with daytime highs Tuesday climbing well into the 60s across the interior. The warmest spots in the lowlands of Lewis County may even reach 70. Mild conditions continue into Wednesday but with increasing clouds and the return of rain by late in the day as the next frontal system pushes through and ushers in a return to cooler temperatures. 12-- End Changed Discussion --&& .AVIATION...-- Changed Discussion --The next frontal system is currently arriving as a warm front spreads widespread rain into W WA. Breezy south winds of 25 to 30 kt are expected this evening into Friday morning. Gusts up to 40 kt are possible for terminals such as KBLI. Some wind shear can`t be ruled out this evening. A mix of VFR/MVFR conditions being observed with the trend continuing overnight and into Friday. Winds are favored to decrease on Friday but localized gusts are possible. Mostly VFR expected into Friday afternoon. KSEA...Rain in the forecast for the airfield this evening with possible reductions in visibility. Ceilings will remain generally between VFR and MVFR this evening before trending more MVFR late overnight into Friday morning. Winds gusts to 25-30 kt are expected this evening as the front moves through, lasting up through Friday morning. VFR is slated to return by Friday afternoon as wind gusts decrease. McMillian-- End Changed Discussion --&& .AVIATION...-- Changed Discussion --The next frontal system is currently arriving as a warm front spreads widespread rain into W WA. Breezy south winds of 25 to 30 kt are expected this evening into Friday morning. Gusts up to 40 kt are possible for terminals such as KBLI. Some wind shear can`t be ruled out this evening. A mix of VFR/MVFR conditions being observed with the trend continuing overnight and into Friday. Winds are favored to decrease on Friday but localized gusts are possible. Mostly VFR expected into Friday afternoon. KSEA...Rain in the forecast for the airfield this evening with possible reductions in visibility. Ceilings will remain generally between VFR and MVFR this evening before trending more MVFR late overnight into Friday morning. Winds gusts to 25-30 kt are expected this evening as the front moves through, lasting up through Friday morning. VFR is slated to return by Friday afternoon as wind gusts decrease. McMillian-- End Changed Discussion --&& .HYDROLOGY...-- Changed Discussion --Several rounds of precipitation this week through early next week will bring rises to area rivers. There is still some potential for flooding on the Skokomish River in Mason County later this weekend, with abundant precipitation possibly moving into the region with significantly higher snow levels. Ensemble guidance continues to show a large range of solutions for precipitation amounts Sunday and Monday so confidence in this scenario remains low at this time.-- End Changed Discussion --&& .SEW WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --WA...Winter Storm Warning until 5 AM PDT Saturday for Cascades of Snohomish and Northern King Counties-Cascades of Whatcom and Skagit Counties. Winter Weather Advisory until 11 PM PDT this evening for Cascades of Pierce and Lewis Counties-Cascades of Southern King County. PZ...Small Craft Advisory until 5 PM PDT Friday 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. Small Craft Advisory until 5 AM PDT Friday for Admiralty Inlet- East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal.-- End Changed Discussion --&& $$