Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
610 FXUS66 KSEW 150955 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 255 AM PDT Wed May 15 2024 .SYNOPSIS...High pressure offshore will continue to provide warm and dry conditions into early Thursday. An upper level trough will dip down south from the British Columbia on Thursday afternoon for cooler temperatures, more cloud cover, and a chance for showers mainly in the northern portions of our region. Unsettled weather looks to continue through the weekend and into early next week, with cooler temperatures and a chance of showers. && .SHORT TERM /TODAY THROUGH FRIDAY/...An upper level ridge mainly located offshore will continue to build into our area today, allowing for the generally warm and dry conditions to continue. Low level onshore flow will keep coastal locations mainly in the lower to mid 60s this afternoon, meanwhile, the more interior locations will likely experience high temps in the low to mid 70s. The aforementioned upper level ridge will begin to flatten into Thursday, leaving room for a upper level trough to move in from British Columbia, increasing onshore flow. A front will then cross into western Washington on Thursday, bringing breezy winds at times, a chance of showers, and cooler temperatures. Showers look meager for the interior with this front, with most of the precipitation aimed at the Northern Cascades. Snow levels look to also gradually drop to around 4000 to 4500 feet on Thursday, but any snow accumulations in the mountains will be light and mainly be limited to the higher peaks in the backcountry. With increased onshore flow, some model guidance is hinting at a convergence zone developing over Skagit and Snohomish counties Thursday evening. High temps will be around the low to mid 60s for the interior, and upper 50s for locations near the coast and areas of water. The upper trough axis will move right across western Washington on Friday, keeping it a cloudy day with the chance for some leftover showers (with the best chance for showers being over the mountains). .LONG TERM /SATURDAY THROUGH TUESDAY/...Ensemble guidance still show several solutions regarding the weekend, but cluster guidance is starting to favor weak troughing over the Pacific Northwest. Although troughing is being favored, it does not look like a particularly wet solution, with most guidance hinting at below normal temperatures and shower chances sticking around through the long term. The best bet for any showers this weekend looks like to be mainly in the higher terrain. Unsettled weather looks to continue into the first half of next week. Mazurkiewicz && .AVIATION...Northwesterly flow aloft will continue over W WA into at least Thursday morning as upper level ridging remains over the eastern Pacific. Surface winds light and northerly for most terminals with only BLI reporting more southerly. Largely VFR conditions area-wide with some high clouds overhead largely east of the Sound or over the western half of the Olympic peninsula. UIL and CLM reporting IFR conditions, however it is worth noting that CLM is bouncing around, sometimes clear, other times with BKN low clouds. Have the lower cigs in a TEMPO group and given the yo-yo nature of the obs, this appears to be the best way to handle it at this time. VFR conditions expected to remain in place for most terminals, however will see cigs gradually lower throughout the day in anticipation of incoming system for Thursday. HQM is worth noting here in that cigs may fall enough to dip down into MVFR this afternoon. KSEA...VFR with mainly high cirrus for the TAF period. While some low confidence hints at MVFR conditions emerging early this morning, a large T-Td difference suggests chances of this close to nil. As mentioned above, cigs will gradually lower throughout the day, however still remaining at or above 10000 ft. Northerly winds 4-8 kts through at least 18Z, then speeds increasing to around 5-10 kts for the afternoon and evening. 18 && .MARINE...High pressure/upper-level ridging will continue to build over the Pacific through the week, resulting in northwest flow translating to north/northwest surface winds. Another round of SCA level winds expected in the Strait starting this afternoon and potentially continuing into Thursday. That said, will be issuing a new round of headlines with the morning forecast package. A stronger push is expected to accompany an incoming frontal system Thursday night and Friday which may need yet another set of headlines. Winds expected to ease for most areas, save perhaps the outer coastal waters this weekend into early next week. Seas will hold around 4 to 6 ft through Friday before increasing 8 to 12 ft from Friday into the weekend, reducing to 6 to 8 ft next week. 18 .HYDROLOGY...The daily hydrology discussion has ended until the start of the next rainy season; it will only be updated as needed. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 5 AM PDT early this morning for Central U.S. Waters Strait Of Juan De Fuca-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-East Entrance U.S. Waters Strait Of Juan De Fuca. && $$