FXUS66 KSEW 102302 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 302 PM PST Sun Nov 10 2024 .SYNOPSIS...A frontal system will move through the region tonight into Monday for lowland rain, mountain snow and the potential of river flooding. Active weather will continue through the remainder of the week, with more lowland rain, mountain snow, potential river flooding, chances of thunder, high surf and breezy conditions. Cooler conditions at the end of next week with more troughing. && .SHORT TERM /TONIGHT THROUGH WEDNESDAY/...We saw a decent break today with mainly high clouds, a few sunbreaks and temps in the 50s. However, we're still on track for a period of active weather starting tonight and continuing past midweek. Main impacts this week will be moderate to heavy rain, mountain snow, chance of thunderstorms, rising rivers with potential flooding, high surf and coastal flooding. Rain associated with the first strong system is reaching the coast now and will spread inland overnight and through Monday. Total rainfall amounts are on the order of 1-3" along the coast and mountains with around 1-1.50" in the interior. Snow levels are initially high (over 6000') but will come down to 4000-5000' on Monday with periods of heavy snow in the north Cascades (including SR 20 and Washington Pass) - a Winter Weather Advisory remains in effect. Expect gusty winds tonight for the coast and north interior with S winds gusting to 25-35 MPH. The weather Monday night and Tuesday turns more showery with a trough moving in. The air mass will be slightly unstable along the coast for a chance of thunderstorms. Meanwhile, this system will generate strong waves with swells of 14-20 feet approaching the coast Monday night into Tuesday. The second, wetter and stronger system, then moves in Tuesday night and Wednesday, keeping the pattern active. The focus and concerns remain the same with an eye on the river levels due to back-to-back wet systems. Several rivers are forecast to reach Action Stage with a few close to Minor flooding. 33 .LONG TERM /THURSDAY THROUGH SUNDAY/...Showers continue into Thursday with deep upper level troughing over Pac NW. Steady rainfall will have ended with rivers likely cresting and receding. The air mass still remains slightly unstable with a chance of thunderstorms (mainly coast). Snow levels will be lower, around 4000', with accumulating snowfall over the higher peaks and passes. Coastal flooding may be a concern with higher astronomical tides and seas still running high (10-15 ft). Friday and Saturday will be cooler with highs in the 40s and lows in the 30s. More rain and mountain snow moving through next weekend with additional incoming systems. 33 && .AVIATION...Southwest flow aloft as an upper low churns offshore. Widely VFR across most terminals (localized MVFR - KHQM & KCLM) this afternoon. MVFR criteria will become more widespread from west to east tonight into Monday morning as a moist front enters with steady rainfall. Increasing southerly surface winds will also become breezy during this time as well. Rainfall is expected to then break into showers as Monday progress while VFR conditions return by noon. KSEA...VFR at the terminal so far this afternoon. However, rainfall is slated to begin around 02-03z with MVFR cigs following overnight and settling around 08-12z. Rainfall is slated to break into showers Monday morning as as VFR conditions return. Light SE winds will turn more southerly after midnight between 10-15 kt with gusts up to 25 to 30 kt. McMillian && .MARINE...Seas have trended lower but winds are increasing ahead of a frontal system arriving tonight/early Monday morning. SCA strength winds expected tonight across most zones. A slight chance (20%) of SCA winds are possible during a brief window on Monday but a better chance exists on Monday night, but still marginal. Then, seas will rebound greatly as a 18-22 ft swell train arrive by Tuesday morning. These seas will also be met with the potential for gales on Tuesday night (60-80% chance across Eastern Strait of Juan de Fuca and coastal zones, and even a 40% chance for Puget Sound). Conditions are slated to remain active throughout the week as a parade of disturbances enters the region. McMillian && .HYDROLOGY...A more significant chance of precipitation is expected through Monday, and again on Wednesday as an active weather pattern returns with weak to potentially moderately strong atmospheric river events coming through the area. The precipitation amounts will be strongly orographically influenced with precipitation totals in the mountains expected to be 3 to 5 inches for both storms except locally over 6 inches on the Olympics for the last one (Wednesday). The succession of storms will increasingly build up soil moisture and river levels throughout this period which will increase the possibility for river flooding. Snow levels vary generally from 4000 to 6000 feet which will impact precipitation type and affect the amount of storm runoff. At this time, the Skokomish River is the only river forecasted to rise into flood stage, and potentially into moderate flood stage during the middle of next week. For other rivers, significant rises are expected with several river forecast points above Action Stage, and flooding could be possible, especially in the Northern and Central Cascades. Flooding extent will continue to depend on rainfall rates, temperatures, as well as snow levels with precipitation that falls with each of these weather systems next week. We will continue to assess the hydrologic conditions and forecasts for any additional areas of potential flooding. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Flood Watch from 10 PM PST this evening through late Monday night for Hood Canal Area-Lower Chehalis Valley Area- Olympics. Winter Weather Advisory from 6 PM this evening to 1 PM PST Tuesday for West Slopes North Cascades and Passes. PZ...Small Craft Advisory until 4 PM PST this afternoon for Grays Harbor Bar. Small Craft Advisory until 4 AM PST 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-West Entrance U.S. Waters Strait Of Juan De Fuca. Small Craft Advisory until 9 AM PST Monday for Admiralty Inlet- Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands. && $$