FXUS66 KSEW 231632 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 932 AM PDT Sun Aug 23 2026 .SYNOPSIS... An upper level trough will continue to make its way across the area this morning, bringing chances of showers and isolated thunderstorms primarily to the mountains and the northern tier of western Washington. Upper level ridging will build into the Pacific Northwest on Monday and Tuesday for warmer and drier conditions. Another upper level low will approach the area around midweek, bringing increasing onshore flow and cooler conditions to western Washington the second half of the week. && .SHORT TERM /TODAY THROUGH TUESDAY/... Cloudy skies this morning and light shower activity moving across Snohomish and Skagit County. Otherwise, no major updates to the forecast this morning. Refer to an updated aviation and fire weather discussion. An upper level trough will continue to make its way inland across the area early this morning. Meanwhile, a surface trough currently extends along the interior of British Columbia, through Vancouver, and down along the Washington coast. A cluster of showers and thunderstorms associated with this feature have remained rather vigorous to the north of the border over the past couple of hours, with latest radar trends showing shower and thunderstorm activity slowly starting to drift southeastward early this morning. Thunderstorms have generally continued to weaken as they drift closer to Washington, however will need to continue to keep an eye on trends through the remainder of the overnight hours as latest hi-res guidance does hint at the possibility of a few storms drifting into portions of the San Juans, Whatcom, and Skagit counties through the early morning hours. Otherwise, expect shower and thunderstorm activity to primarily become confined to the Cascades by this afternoon and to gradually wane throughout the day as the upper level trough pushes off to the east and ridging starts to build in from the west. Widespread cloud cover across the area will take a bit longer to scatter today, helping to keep temperatures slightly cooler and primarily in the low to mid 70s across the interior and in the mid 60s along the coast. Upper level ridging will then build into the Pacific Northwest on Monday, with the ridge axis shifting eastward over the Intermountain West by Tuesday. This will bring a warming and drying trend to western Washington the first part of the week, with Tuesday expected to be the warmest day across western Washington. Afternoon high temperatures will climb into the 80s across the interior lowlands and into the low 90s across the Cascade valleys by Tuesday, reintroducing Moderate HeatRisk to portions of these areas. Surface flow will also transition to northerly and then offshore at times, which may allow for some smoke transport from ongoing wildfires across British Columbia and eastern Washington to make its way back into western Washington at times through the early part of the week. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... Ensemble guidance remains in decent agreement with an upper level low approaching the Pacific Northwest on Wednesday. This would bring the return of onshore flow and cooler conditions to western Washington the second half of the week. Chances of precipitation will also increase Wednesday and Thursday, though overall amounts look to remain light at this time. Will need to keep an eye on any thunder potential for the area, though probabilities at this time remain at around 10 percent or less. Temperatures will generally trend near to slightly cooler than normal the second half of the week, with afternoon highs topping out in the low to mid 70s across the interior and mid 60s along the coast. Ensemble guidance suggests the upper level trough will remain an influence across the area heading into next weekend, which would continue to promote onshore flow and near to slightly below temperatures across western Washington. 14 && .AVIATION... An upper level trough continues to move east of the area this morning with northwest flow behind the trough. Upper ridging builds in tonight with the flow becoming westerly. Low level onshore flow today becomes northerly tonight into Monday. VFR/MVFR cigs this morning will improve to widespread VFR around midday, with clouds becoming more BKN/SCT this afternoon. VFR into tonight with areas of LIFR stratus along the coast and Strait of Juan de Fuca early Monday AM. Localized fog may develop in river valleys into early Monday as well. W/SW winds transitioning NW for some terminals this afternoon. KSEA...VFR cigs ranging 030 to 050 this morning. Cigs slowly becoming BKN into the afternoon before clearing into this evening. VFR expected then tonight into Monday. Southwest winds becoming N/NW around 23-01z, then remaining NE tonight. JD && .MARINE... High pressure rebuilding over the coastal waters today will remain through Tuesday. Thermally induced surface trough along the coast Monday will dissipate Monday night. A weak frontal system will move across the waters Wednesday night. High pressure rebuilds over the area Thursday. Small craft advisory westerlies in the Central and Eastern Strait of Juan de Fuca Tuesday night otherwise winds 20 knots or less through the period. Seas remaining in the 3 to5 foot range through the week. Felton && .FIRE WEATHER... An upper-trough is progressing across the region today. As it pushes off, showers will linger this morning along with a slight chance (less than 15%) of thunderstorms. Overall chances of showers and thunderstorms will then decrease substantially this afternoon and evening as the upper trough exits the region. An upper level ridge will then build into the area Monday and Tuesday, bringing brief periods of low- level offshore flow as a thermal trough builds along the coast and pushes inland overnight into Tuesday. Elevated fire weather conditions are likely across the Cascades on Tuesday with the warm and dry pattern and with relative humidities dipping into the low to mid 20s. Another upper level trough will arrive in the middle of next week, bringing the return of onshore flow- as well as chances for more showers and the potential for thunderstorms. Upper- level troughing then looks to linger into the weekend. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$