Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
379 FXUS66 KSEW 152133 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 233 PM PDT Tue Sep 15 2026 .SYNOPSIS... Cloudy skies will continue to scatter today as high pressure promotes a warming and drying trend through Thursday. Near normal temperatures and partly cloudy conditions are expected to return through the weekend and into early next week with continued low level onshore flow. && .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... Dry northerly flow will continue to fill into western Washington this afternoon as a positively tilted trough shifts south of the area. This will allow clouds to continue to scatter out for most lowland areas, revealing clear skies by this evening. Temperatures on the cooler side will continue today with highs generally in the mid 60s to lower 70s. A high pressure ridge will slowly build into the region tonight through Thursday, bringing a warming and drying trend to western Washington. Clear skies tonight combined with recent light rain and light winds will allow fog to form in fog prone areas like the southern Interior early Wednesday morning, burning off by the afternoon. Temperatures will warm up to near-normal Wednesday under mostly clear skies, with highs generally in the mid 70s. A thermal trough building along the coast will shift inland on Thursday, inducing cooling along the coast with even warmer temperatures further inland. Temperatures Thursday will be the warmest of the week, with highs in the mid to upper 70s and around 80 degrees for some areas along the Cascade foothills and valleys and over the southern Interior. && .LONG TERM /FRIDAY THROUGH TUESDAY/... High pressure offshore will continue to influence the weather pattern over the weekend and into early next week, maintaining seasonable temperatures and dry conditions. Onshore flow will continue to promote morning cloud cover with plenty of sun breaks in the afternoons. Forecast models continue to hint at a potential pattern change early next week, though deterministic models continue to push back the timing of an approaching trough as the Pacific ridge holds on. 15 && .AVIATION... Flow aloft will turn northerly as a trough continues to dig southward tonight into Wednesday. Ceilings are beginning to lift and scatter this afternoon as shower activity moves east of the Cascades. Remaining MVFR ceiling decks will lift up to VFR through the afternoon and evening as clouds clear out. Light winds out of the north at 5 to 10 kt will decrease to under 5 kt tonight (calm or light and variable in a few spots). There remains a 20-30% of IFR/LIFR conditions for a majority of central, and south interior terminals as well as the Pacific Coast Wednesday morning between 12 and 18Z. The forecast soundings in the morning depict widening dew point depressions just above the surface. The drier air aloft will likely lead to areas of patchy fog in the morning (versus widespread advection fog), and be shallow in nature. Clear skies will takeover the IFR/LIFR conditions late Wednesday morning/afternoon. Winds Wednesday will pick up out the north 5 to 10 kt. KSEA...VFR through the evening/early tonight with north winds 5 to 10 kt decreasing to 5 kt overnight. There remains a 20-30% chance of IFR conditions in the morning. Model guidance has 10-15% LIFR probabilities of vicinity fog to the north and south of the terminal. Time period for formation is from 12-18Z, with clear skies Wednesday afternoon. Winds increase out of the north Wednesday 5-10 kt. HPR && .MARINE... A thermal trough will build local low pressure along the coast Wednesday into Thursday. This will cause the winds to briefly turn offshore. Once the thermal trough moves inland on Friday, the onshore flow will return with weak systems passing to the north this weekend. The likelihood of hazardous winds during the next seven days over the waters is low, but a few portions of the coastal waters and the Strait of Juan de Fuca may see wind gusts approach 20 kt with the weak system passing through early next week. Seas will hold around 3-5 or 4-6 ft through the forecast period. HPR && .FIRE WEATHER... A brief warming and drying trend will kick off today and continue into Thursday as high pressure builds offshore. Surface winds will briefly turn offshore on Wednesday as a thermal trough builds along the Pacific coast. Weak offshore flow will continue through Thursday, causing additional drying with relative humidity values bottoming out in the mid 20s to low 30s in the North Cascades and lowlands south of the Puget Sound. The thermal trough will shift inland on Thursday ahead of the return of onshore flow, which will minimize fire weather concerns through the weekend and into early next week. 15 && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$