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Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
536 FXUS66 KSEW 122112 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 212 PM PDT Mon Aug 12 2024 .SYNOPSIS...Upper troughing over the region will promote onshore flow and cooler temperatures through Tuesday. Isolated thunderstorms will be possible across the North Cascades today and Tuesday. Brief ridging will build Wednesday into Thursday. An upper low offshore may bring more widespread precipitation potential over the weekend. && .SHORT TERM /TONIGHT THROUGH THURSDAY/...Mostly cloudy conditions across Western Washington this afternoon with continued onshore flow. There remains a chance for thunderstorms this afternoon over the North Cascades, with NBM probabilities generally 20-30%, highest along the Cascade crest in this region. Troughing will continue through Tuesday, allowing for continued cooler conditions. High temperatures both today and Tuesday will be in the mid 60s to low 70s. Ridging will build briefly into British Columbia Wednesday into Thursday. This will allow for some additional clearing, especially Wednesday afternoon. Temperatures will also warm a bit Wednesday and Thursday, but remain below normal, with highs generally in the mid 70s for the interior and mid 60s for the coast. .LONG TERM /FRIDAY THROUGH MONDAY/...Ensembles are consistent in troughing developing offshore Friday with an upper low lingering offshore of Washington/Oregon into early next week. Initially, precipitation potential will generally be confined to the Cascades on Friday, along with the threat for thunderstorms in this area. Increasing moisture is expected Saturday and Sunday with the upper low position and southerly flow aloft, introducing more widespread shower chances over Western Washington. We will also have to monitor the potential for convection, particularly later Saturday into Sunday morning, given the increasing southerly flow aloft. NBM probabilities at this time for much of Western Washington are around 15% for thunderstorms during this period. Showers chances may lingering into Monday with the upper low offshore. Temperatures will likely remain below normal, mostly in the mid 60s to mid 70s over the weekend. JD && .AVIATION...Light and variable flow aloft with an upper level trough moving over western Washington. Stratus has lifted and broken up a bit, allowing for ceilings to rise to VFR. VFR conditions will continue though this evening until stratus will redevelop and lower through the night into tomorrow morning. Widespread MVFR ceilings with locally lower conditions possible, especially along the coast. Expecting a similar evolution tomorrow to today where ceilings slowly rise back to VFR and become broken without fully clearing out. Winds remain west to southwesterly 5 to 10 kt, with a few gusts up to 15 kt this afternoon. KSEA...VFR conditions through this evening, dropping back down to MVFR early tomorrow morning after 12Z then lifting back up around 18Z Tuesday. Winds continue to remain southwesterly 5 to 10 kt. LH && .MARINE...Broad high pressure over the East Pacific will continue onshore flow over the area waters. Diurnally driven pushes down the Strait of Juan de Fuca will occur each evening with no signs of SCA level winds for the next few days. Marine stratus and fog each morning may locally limit visibility at times. The push Thursday afternoon looks to be the strongest of the week and may get close to SCA criteria. Seas will remain around 3 to 5 ft through the rest of the week. LH && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$