Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
919 FXUS66 KSEW 170332 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 832 PM PDT Thu May 16 2024 .SYNOPSIS...Upper-level troughing through much of the upcoming weekend. With it, cooler and showery conditions are in store. Brief ridging is expected to start the upcoming week before troughing rebounds through the middle of next week. && .UPDATE...Convergence zone showers continue across Snohomish County this evening. Hi-Res guidance shows the activity spreading south into King county late into the evening before dissipating overnight. Precipitation forecast is on track, so no major changes to the forecast below (minus a refreshed aviation discussion). HPR && .SHORT TERM /TONIGHT THROUGH SUNDAY/...As mentioned, upper- troughing is currently positioned over the region. At the surface, a frontal boundary is pushing towards western Washington out of BC. With it, increased onshore flow and spotty precipitation is being observed across the area. Light rain showers are in the forecast this evening along with convergence activity. Most of the precipitation will fall in higher elevations with aid of orographic enhancement. High-res guidance has the PSCZ focused mainly over Snohomish County before drifting southwards over King County overnight tonight. With troughing overhead, cooler temps aloft are expected with snow levels around 3,000-3,500 ft. Overnight lows are to fall into the low to mid 40s. Lingering showers are possible into Friday as we`ll be on the backside of the upper-trough. Nevertheless, drier conditions are expected but cooler temps are to remain with highs slightly below average. Then, the next upper-low is on track to enter on Saturday with another round of showers. However, a drying will try to set up on later on Sunday as transient ridging moves overhead by the nighttime hours. Weekend highs are to top out in the mid 50s to lower 60s with overnight lows in the 40s. .LONG TERM /MONDAY THROUGH THURSDAY/...Ridging to remain over the region on Monday but it won`t be long lasting. Active weather looks to resume around the Tuesday-Wednesday timeframe as another upper-low out of BC dives south into the region. Temperatures are to be around average for Monday but, cooler temps along with wet weather looks to pick back up as the week continues. McMillian && .AVIATION...Westerly flow aloft will continue as an upper trough moves across the Pacific Northwest. Post-frontal airmass continues this evening with a convergence zone located across portions of Snohomish and King Counties. Generally VFR this evening with areas of MVFR with isolated showers, and MVFR/IFR near the convergence zone. The convergence zone will slowly slide southward across King County and into the Cascades tonight, with shower activity mainly in the Cascades tonight. BKN VFR tonight with areas of MVFR and some clearing as well. High end MVFR to low end VFR possible into the morning, particularly east of Puget Sound. Otherwise, continued VFR into the afternoon. Breezy SW to NW winds this evening will taper tonight. KSEA...VFR cigs this evening with a convergence zone north of SEA. Generally SCT/BKN VFR tonight into Friday. Shower activity mainly in the Cascades tonight. Brief period of high end MVFR possible Friday morning, but confidence is low. Winds will primarily be southerly into Friday, but should note at least a slight chance of VRB winds tonight, mainly between 05-08z as the convergence zone moves southward. JD && .MARINE...An incoming frontal system will keep conditions breezy across the area waters into Friday. Small craft advisories will be in effect for all area waters as a result. Seas across the coastal waters will build towards 10 ft on Friday, likely resulting in an extension of small craft headlines for the coastal waters zones. High pressure offshore looks to remain persistent into next week. With lower pressure situated inland, expect onshore flow to persist through the forecast period. Another frontal system looks to move across the area waters early next week and may result in another round of headlines. Seas currently hovering at 4-6 ft over the coastal waters this afternoon. Expect seas to build towards 9-12 ft on Friday before gradually subsiding back to 5-7 ft over the weekend and into early next week. 14 && .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 11 AM PDT Friday for Admiralty Inlet- 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-Northern Inland Waters Including The San Juan Islands-West Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory until 5 AM PDT Friday for Puget Sound and Hood Canal. && $$