FXUS66 KSEW 261051 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 351 AM PDT Mon Aug 26 2024 .SYNOPSIS...Upper level ridge over the area weakening today. Upper level trough and associated front moving through late tonight/early Tuesday morning. High pressure building back in Tuesday afternoon and Tuesday night. Upper level ridge over Western Washington Wednesday into Saturday with the ridge moving east Sunday. Upper level off the Northern California coast beginning to move northeast Sunday. && .SHORT TERM /TODAY THROUGH WEDNESDAY/...Satellite imagery shows middle and high level clouds out ahead of an approaching system over the far northern portion of the area early this morning. Mostly clear skies over the remainder of Western Washington. Fog starting to form over the Southwest Interior with visibility at Olympia at 3 am/10z 1/2 of a mile. Temperatures were in the 50s. Increasing middle and high level clouds over the area today as an upper level trough and associated front approach from the northwest. Front near Haida Gwaii early this morning. The front will still be northwest of the area late this afternoon. Chance of rain in the afternoon northwest of a line from Bellingham to Hoquiam. Even with the increasing clouds highs in the mid 60s to mid 70s. Upper level trough moving through late tonight/early Tuesday morning. Narrow front associated with the trough will bring a brief round ( 2 or 3 hours ) of rain from the Puget Sound northward. Winds increasing with and behind the front especially near the Strait of Juan de Fuca and over the Northwest Interior. Lows tonight in the 50s. Not much of a cool pool of air behind the front so post frontal showers will come to an end pretty quickly Tuesday morning. Convergence zone developing between Seattle and Everett with showers lingering a little longer in this area. Northerly flow aloft developing Tuesday afternoon will help decrease the cloud cover. Highs Tuesday below normal, mostly in the 60s. Upper level ridge building over Western Washington Tuesday night and Wednesday. 500 mb heights in the mid 580 dms by 00z Thursday. Northwesterly surface gradients will knock a couple of degrees off the highs especially near the water. Wednesday morning will be the coolest morning in a while. Another touch of fall with lows in the mid 40s to mid 50s. The last time Seattle had a low below 50 degrees was over two months ago ( 49 degrees June 19th ). Highs in the upper 60s to mid 70s. .LONG TERM /THURSDAY THROUGH SUNDAY/...Upper level ridge remaining over Western Washington through Saturday. Low level flow going weakly offshore later Thursday into Friday with a thermally induced surface trough along the coast. Upper level ridge starting to drift east Saturday with the low level flow turning onshore late in the day. Possibly problematic upper level low off the Northern California coast starting to move northeast Sunday. Models hinting at some convection over the Oregon Cascades Sunday afternoon. Will be keeping an eye on how the feature evolves this week. For now the upper level ridge continuing to move east Sunday with increasing low level onshore flow cooling high temperatures 5 to 10 degrees. Highs Thursday 70s to lower 80s, Friday and Saturday mid 70s to mid 80s and Sunday upper 60s and 70s. Felton && .AVIATION...Southwest flow aloft will increase across Western Washington today ahead of a frontal system and trailing upper level trough that will move across the region late tonight. Aside from patchy LIFR/IFR in stratus this morning, VFR conditions are expected with increasing high and mid level moisture. MVFR ceilings in light rain will develop along the coast this afternoon then spread to the interior lowlands by late this evening. Gusty post-frontal surface winds are expected late tonight through much of Tuesday morning. KSEA...Increasing high/mid level clouds today with ceilings lowering to MVFR in light rain near or after 06Z tonight. Surface winds light and variable early becoming southwesterly 5 to 10 knots late this morning through the afternoon. Winds will become gusty behind the front late tonight. 27 && .MARINE...A frontal system will reach the coastal waters this evening then sweep inland overnight tonight. Post-frontal onshore flow behind the system will lead to small craft advisory conditions across the coastal waters in the form of gusty northwest winds and choppy short period seas. Additionally, westerlies will increase through the strait with gusts potentially approaching gale force briefly early Tuesday morning near the east entrance. Surface ridging strongly rebuilds offshore for the second half of the week while lower pressure remains in place over the interior for a return to a more seasonal pattern of varying degrees of diurnally driven onshore flow. 27 && .CLIMATE...With the forecast temperatures the remainder of the month there is a good chance August 2024 will be the coldest August in Seattle since 2011. The chances for a 90 degree plus day in Seattle really drop off this time of year. Out of the 267 90 degree plus days since records started at Seattle-Tacoma airport in 1945 only 24 (9%) of them have occurred on August 26th or later. Felton && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory from 11 PM this evening to 11 PM PDT Tuesday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory from 2 AM to 5 PM PDT Tuesday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. && $$