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Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
382 FXUS66 KSEW 150330 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 830 PM PDT Wed Aug 14 2024 .SYNOPSIS...Afternoon sunshine and near normal temperatures through Friday. The pattern looks to trend wetter into the weekend with what amounts regarding good chance of widespread precipitation for much of the region, with a threat of thunderstorms for the lowlands. && .SHORT TERM /TONIGHT THROUGH SATURDAY/...Forecast remains on track this evening with weak high pressure over the region. No updates required tonight with the previous sections following below. The aforementioned high pressure will get replaced by weak troughing over the Pacific Northwest starting on Thursday, with more cloud cover, cooler temps, and mountain showers. Along with mountain showers, there is a chance of thunderstorms primarily in the North Cascades Thursday afternoon and evening. High temps will generally be in the mid 70s. An upper level low centered in Canada will gradually drop down and center just offshore our area on Friday, with a continued chance of showers and thunderstorms primarily in the North Cascades. This upper level low will continue to spin offshore on Saturday, placing western Washington in a moist S/SW flow. Latest guidance suggests widespread shower coverage for most of the area on Saturday. Along with increased precipitation chances that we have not seen in a while, there is a threat of thunderstorms for most of the lowlands and Cascades. Probabilistic guidance suggests around a 15-25% of thunderstorms late Saturday afternoon into the evening hours, increasing to around 30% through the overnight hours into early Sunday morning. There is definitely some ensemble uncertainty regarding the position of the upper level low offshore, which could lead to differences in rain amounts, timings, and thunderstorm chances. As for now, we will continue to monitor the threat as new guidance becomes available. .LONG TERM /SUNDAY THROUGH WEDNESDAY/...Ensemble guidance continues to highlight S/SW flow for a chance of showers and thunderstorms through Sunday. Conditions look to trend drier heading into Tuesday, with ensembles struggling on precipitation chances later on in the week. Mazurkiewicz && .AVIATION...Light southeast flow expected tonight into Thursday with weak high pressure over the area. BKN mid level clouds continue across portions of Puget Sound this afternoon, with VFR for most areas. Stratus will further develop along the coast into this evening and spread inland into Puget Sound Thursday morning. Generally MVFR/IFR with stratus in Puget Sound during this period with LIFR cigs along the coast. Cigs will improve to VFR Thursday afternoon. Lower vsbys possible tonight along the coast. W/NW winds will become lighter tonight. KSEA...VFR mid level cigs this afternoon. VFR will continue into early tonight. MVFR stratus expected Thursday morning, generally 12- 18z. There is approximately a 15% chance of IFR cigs during this period. Cigs will improve to VFR Thursday afternoon. W/NW winds into this evening at 5 to 8 kts will become light NE tonight and transition S/SW Thursday morning. JD && .MARINE...Onshore flow pattern continues through this week across the area waters with diurnally driven westerly pushes through the Strait of Juan de Fuca. Brief SCA wind gusts may occur this evening into early tonight for portions of the central and eastern Strait of Juan de Fuca, but they are not expected to be widespread. Confidence is a bit higher in SCA winds through the Strait of Juan de Fuca Thursday evening into Thursday night with increasing west winds. Otherwise, northwest winds continue over the Coastal Waters through Saturday. Areas of lower visibilities due to fog is possible tonight for the inner Coastal Waters. In addition, there is a threat for thunderstorms, especially for the inner waters Saturday afternoon through Sunday morning. Seas will generally remain 3 to 5 feet through Saturday. JD && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$