Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
578 FXUS66 KSEW 231529 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 829 AM PDT Sun Jun 23 2024 .SYNOPSIS...An upper level trough will produce clouds, cooler temperatures, and a few showers across Western Washington today. The trough will weaken tonight and a ridge of high pressure aloft will begin to rebuild into the area Monday. The ridge will strengthen as it shifts eastward on Tuesday for dry conditions and warmer temperatures. Another trough arrives Wednesday into Thursday for showers and cooler temperatures once again. A weak ridge late in the week will lead to drier conditions and near normal temperatures. && .UPDATE...No major changes to the forecast. Expect off an on light showers to continue throughout the day today, with a noticeable cool-off in high temperatures today in the low to mid 60s. Please see the discussion below for more details (as well as a refreshed aviation). HPR && .SHORT TERM /TODAY THROUGH TUESDAY/...Clouds have filled in across most of Western Washington early this morning ahead of an upper trough moving into British Columbia. Spotty showers have already been observed across coastal areas and we should see some weak convergence zone activity develop across Skagit and Snohomish counties later this morning. QPF will be minimal...a few hundredths at best. High temperatures will be back below normal...in the 60s across most of the lowlands. The upper trough weakens tonight into Monday as it shifts eastward across interior British Columbia and this will allow upper ridging to begin rebuilding into the area. Most areas should see some sunshine return Monday afternoon with temperatures rebounding to near seasonal norms. Upper ridging gains amplitude as it shifts eastward into the northern Rockies later Tuesday. Interior temperatures will warm into the 70s while onshore flow keeps most of the coast firmly in the 60s. .LONG TERM /WEDNESDAY THROUGH SATURDAY/...Models remain consistent with an upper trough moving into the region Wednesday and Thursday. This one has a more southward trajectory than the current one and looks to provide much of the region with a decent chance at some measurable precip. And as one would expect, temperatures will cool back to below normal levels midweek. The upper trough shifts eastward into the Northern Rockies by the end of week allowing weak upper ridging to briefly rebuild. With continued onshore flow, temperatures will be held around seasonal levels...60s coast...70s inland. 27 && .AVIATION...Upper level trough over Western Washington today moving east tonight. Zonal flow aloft tonight and Monday. Onshore flow will persist in the lower levels through Monday. Satellite imagery shows clouds have made it all the way to the Cascade crest this morning, with ceilings at area terminals mainly a mix between VFR and MVFR. Light showers will possible today, with greatest chances of shower activity expected for terminals along the coast and KPAE northward. Expect ceilings to become more widespread VFR between 20Z-23Z. High-res guidance does indicate a weak convergence zone developing over northern King and Snohomish counties this afternoon and evening, which could bring localized MVFR ceilings in showers to KPAE at times. VFR ceilings look to continue for the majority of area terminals into Monday morning, with the exceptions being KHQM along the coast, where lower ceilings look to move back in tonight, and KPAE in any lingering convergence showers. KSEA...VFR ceilings, though could still see some brief periods of MVFR through the morning hours today. Expect ceilings to be mostly VFR this afternoon and evening. High-res guidance indicating PSCZ will stay to the north of the terminal. Southwest wind 10 to 14 knots, with gusts to 20 kt possible at times through the day. Winds will ease back to 4-8 kt after 03Z. 14 && .MARINE...Weak high pressure will build back over the coastal waters and interact with lower pressure inland today through Tuesday. Another frontal system will reach the waters Wednesday. High pressure will rebuild over the coastal waters Thursday. Diurnal westerly pushes through the Strait of Juan de Fuca could result in small craft advisories for the Central and Eastern Strait Tuesday through Thursday in the evenings. Swell near 4 feet this morning building to 5 to 7 feet tonight into Monday. Felton && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$