Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
372 FXUS66 KSEW 080348 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 848 PM PDT Mon Sep 7 2026 .UPDATE... Satellite imagery shows middle and high level clouds wrapping around the upper level trough over Eastern Washington moving into the northern portion of the area. Mostly clear skies elsewhere. Flow aloft turning northerly overnight decreasing the amount of middle and high level clouds. With the longer nights and light northerly gradients possibility of fog/low stratus forming near the Strait of Juan de Fuca and Puget Sound as well as over Lake Washington. Marine push not strong enough to advect stratus east of the Puget Sound overnight. Sunny Tuesday after the areas of morning low clouds and fog. Low level flow turning light offshore later tomorrow into Wednesday. Wednesday looks to be the warmest day since August 25th. Will make quick update for the fog/low clouds Tuesday morning. The rest of the forecast in good shape. Felton && .SYNOPSIS... Low pressure will move east of the Cascades tonight. High pressure will move in Tuesday and Wednesday for drier and warmer conditions. A pair of systems look to move through Thursday through the weekend for more chances for showers and cooler weather. && .SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/... Water vapor imagery shows Washington remaining under the influence of the broad upper level trough that has been sitting over the area since last week finally beginning to eject eastward towards Montana. Chances for light showers will continue this afternoon, but expect clouds to slowly decrease in coverage into this evening. Highs will remain in the mid to upper 60s, perhaps into the low 70s for places that see the most sun. Clearer skies expected this evening though expect another marine layer to start the day Tuesday. Lows in the upper 40s to mid 50s. Upper level ridging will briefly build across the area through Wednesday. Weak surface thermal troughing will develop on Tuesday and will allow the low level flow to turn offshore. Winds will not be very strong but it will allow for clear skies and temperatures to rise into the mid 70s on Tuesday, then into the upper 70s to low 80s on Wednesday. Low temperatures will also noticeably increase, up into the mid to upper 50s by Wednesday night. 62 && .LONG TERM /THURSDAY THROUGH MONDAY/... Ensemble guidance remains pretty well clustered through Thursday as the next disturbance drops down across the Pacific Northwest. This will bring a return of cooler marine air, cloud cover, rain chances. Typically windy locations may see increased breezes by Thursday evening in the stronger onshore low-level flow. Confidence begins to decrease a bit by Friday and into the weekend as the ensembles continue to depict a fairly large range of possible outcomes. Specifically, much of this uncertainty centers around the depth and timing of the next upper trough swinging across the region. However, regardless of specifics, there`s not a significantly strong signal for impactful weather. Expect increased clouds, cooler temperatures, and rain chances when the trough swings across, and slightly warmer and drier conditions once it passes. Cullen && .AVIATION... Northerly flow aloft as an upper level over Eastern Washington continues to move east. VFR conditions this evening with VFR conditions continuing in the overnight hours. IFR stratus forming along the coast after 09z will not make it into the interior terminals. Could see low stratus and fog form near the Puget Sound and Lake Washington 12z-16z with possible LIFR ceilings at KPAE and KCLM. LIFR conditions also possible at KOLM between 12z-16z. What little fog and low cloud that does form over the interior will be shallow with VFR conditions all areas except KHQM by 17z. KHQM clearing out by 19z. KSEA...VFR ceilings through Tuesday. Low clouds could form near the Puget Sound and Lake Washington 12z-16z but at this point it does not look like the clouds will make it to the terminal. Northerly wind 4 to 8 knots. Felton && .MARINE... High pressure will gradually build across the coastal waters through Wednesday. Winds will begin to increase tomorrow and could reach close to Small Craft Advisory thresholds by Wednesday night into Thursday (50-80% chc) over the outer coastal waters as the pressure gradient tightens due to an approaching frontal system from the north. Winds through the Strait of Juan de Fuca begin to increase Wednesday evening, with higher confidence of small craft winds through late Thursday morning. The frontal system weakens as it moves through on Thursday, allowing winds to ease area-wide. Another system may move through the waters late Friday into Saturday, but is currently not showing a signal for stronger winds. Seas remain 3-6 ft through Wednesday. Seas will increase Wednesday night into Thursday up to around 7-10 ft and become steep as short period waves from the stronger winds over the coastal waters begin to dominate. 62 && .FIRE WEATHER... Warmer and drier conditions develop across the region Tuesday and especially Wednesday. Given the recent cool and moist conditions, this will generally return the fire weather conditions trending back back to seasonal levels of concern. Light offshore flow late Tuesday into Wednesday could yield poor overnight RH recoveries on the ridges in Cascades and Olympics, with daytime humidities approaching critical thresholds. However, given the short-lived period of warmer conditions and offshore flow (more humid air returns by late Thursday with breezy onshore flow), do not expect a significant ramp up in the fire weather risk. Cullen && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$