Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
200 FXUS66 KSEW 141555 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 855 AM PDT Mon Sep 14 2026 .SYNOPSIS... Upper level low well to the east this morning with northwesterly flow aloft. Upper level trough moving down from the north moving through Tuesday morning. Upper level ridge building offshore Tuesday night will move over the area Wednesday. Brief spell of offshore flow Wednesday night with a thermally induced surface trough along the coast. The trough will shift inland Thursday. Flat upper level ridge into the weekend with low level onshore keeping temperatures near normal. && .SHORT TERM /TODAY THROUGH WEDNESDAY/... The latest forecast remains on track this morning with no updates. Northwesterly flow aloft with low level onshore flow will produce a mostly cloudy day today. Weak convergence this morning over Snohomish and Northern King county could produce a light shower or some drizzle. With the cloud cover high temperatures will remain below normal, in the 60s. Upper level trough dropping down the British Columbia coastline still north of Western Washington at 12Z Tuesday. Low level onshore flow weakening with some breaks in the cloud cover in the evening. With all the low level moisture around from the rains Sunday clouds filling back in overnight. Lows in the mid 40s to mid 50s. Upper level trough moving through Tuesday morning with isolated light showers or areas of drizzle over the northern portion of the area. Dry northerly flow aloft behind the trough in the afternoon with skies clearing from the north. Another day of below normal high temperatures in the 60s. Skies continuing to clear Tuesday night. Light flow in the lower levels. With the longer nights this time of year plus the low level moisture areas of fog forming. Lows in the mid 40s to lower 50s. There is an outside chance Seattle drops into the 40s. The last time Seattle had a low in the 40s was June 8th ( 49 degrees ). Upper level ridge building offshore nosing into the area Wednesday. What fog that does form will be shallow and dissipate in the morning. Under sunny skies high temperatures warming into the 70s. Felton && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Extended models in good agreement with a thermally induced surface trough developing along the coast Wednesday night for a brief spell of light offshore flow. The trough shifts inland during the day Thursday. Lows in the upper 40s to mid 50s. Highs in the 70s with the warmest locations getting into the lower 80s. Upper level ridge remaining over the area Thursday into the weekend with varying degrees of onshore flow. Highs dropping back into the mid to upper 60s along the coast with the increase in the onshore flow Friday. Highs over the interior in the 70s. Marine layer along the coast in the late night and morning hours over the weekend staying west of Puget Sound. High temperatures cooling during the weekend into the mid 60s on the coast and mid 60s to lower 70s inland. Felton && .AVIATION... Northwest flow aloft will shift more westerly late tonight as a weak upper trough dips southward into Western Washington. Low level onshore flow will weaken today. Residual low level moisture from a departing system along with onshore flow will lead to a mixed bag of MVFR and VFR ceilings this morning. Ceilings will gradually lift back to VFR most areas after 21Z this afternoon. KSEA...Periods of high end MVFR ceilings are expected this morning before lifting to VFR this afternoon. Surface winds southerly 7 to 10 knots will ease to southwesterly 4 to 7 knots this afternoon. A gradual shift to light north/northeasterly wind is expected around 04Z to 07Z tonight. 33/27 && .MARINE... Onshore flow will weaken today then turn more northerly on Tuesday. Thermally induced low pressure expanding northward along the coast will lead to more northerly or offshore flow Wednesday and Thursday. Onshore flow will return Friday into the weekend as a series of systems pass well north of the area. 27 && .FIRE WEATHER... Fire weather concerns remain minimal through the next week. Rains from Sunday increased fuel moisture across at least the southern half of the region. The pattern turns drier and warmer mid to late week, with the surface winds going light offshore briefly Wednesday night into Thursday. This will drop daytime minimum relative humidity just below 30%, which will allow more reactive fuels to start to dry out. The offshore flow will be short lived with the low level flow turning back onshore Thursday night into Friday easing any fire weather concerns. Felton && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$