Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
399 FXUS66 KSEW 072037 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 137 PM PDT Mon Sep 7 2026 .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 low exits western Washington. Mixed bag of conditions out there this afternoon as MVFR low clouds continue to linger throughout the interior. A mix between MVFR to VFR will continue this afternoon as clouds slowly lift up this evening (00z). VFR will continue overnight and into Tuesday, the exception being HQM, OLM, and PWT, where low clouds will develop 08z-13z, with MVFR/IFR intermittently throughout the early morning. N/NE winds will stay around 3 to 6 knots throughout the period. KSEA...VFR ceilings this afternoon with some low to mid level clouds around the terminal. Can`t rule out brief MVFR ceilings at times later this afternoon, but VFR should prevail throughout the remainder of the period. SW winds this afternoon 4 to 8 knots will transition to more N/NE this evening and into Tuesday morning, decreasing to 3 to 6 knots. Latest guidance suggests a 30% chance of MVFR clouds developing at the terminal early Tuesday morning, but confidence remains fairly low as the air mass continues to dry out - leading to most likely VFR conditions. Mazurkiewicz && .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. && $$