FXUS66 KSEW 101651 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 851 AM 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 /TODAY THROUGH TUESDAY/...A little break between systems this morning, except for King County where a few light showers persist. Otherwise, we're still on track for rain spreading back into western WA late this afternoon and evening, with impacts detailed below. 33 Previous discussion...A deep upper level low with an associated front remains offshore early this morning, but will gradually move closer to western Washington this afternoon. Dry weather this morning will be brief as this system moves inland this afternoon, spreading rounds of moderate to heavy precipitation at times, especially along the coast, Olympics, and the Cascades. The heaviest times of precipitation will be later tonight into Monday morning, where we could see 2-3" in the Cascades and the coast, 3-4" in the Olympics, and around 1-1.5" for lowlands, in terms of precipitation. Heavy rainfall during this time will bring the Skokomish River in Mason County into flood stage, where a Flood Watch continues to remain in effect. Snow levels will initially be 5000-6500 feet tonight before falling to 3500-4500 feet later Monday. Snow accumulations can be expected at SR 20 and Washington Pass, therefore, the Winter Weather Advisory for the North Cascades still remains in effect. A foot of snow is also possible at Mount Baker. Locally breezy conditions likely Monday morning, with the breeziest winds along the coast and north interior (around 25 to 35 mph). In addition, seas look to build Monday night anywhere from 18 to 23, which could lead to high surf along the coast. The air mass also continues to be unstable, with chances of thunderstorms along the coast through Tuesday. As we head into Tuesday, rain will be lighter than Monday and we will see rivers briefly lower but it will be brief as a more wetter system arrives Tuesday night into Wednesday morning. .LONG TERM /WEDNESDAY THROUGH SATURDAY/...A wetter, more active system will move through the area on Wednesday that will lead to more focused rain over the Olympics and the Cascades with additional concerns for river flooding into Thursday. Additional rivers are forecasted to pass Action Stage, and be perhaps close to Minor flood stage. Refer to the Hydrology section below for more details concerning river flooding. A stronger shot of snow is likely for the Cascades as well, especially in the Northern and Central Cascades. Snow levels look to be around 4000 to 4500 during this time. Additionally, coastal flooding may be a concern with higher astronomical tides and combined seas running a bit high. Cooler conditions will continue into the weekend as upper level troughing settles over the Pacific Northwest. High temperatures seem to be a touch cooler, in the mid to upper 40s. Snow levels take a dip into the 2500-3000, where mountain snow returns along with lowland rain. Mazurkiewicz && .AVIATION...Southwesterly flow aloft will increase today as the next disturbance approaches the region. With a stable air mass, abundant residual low-level moisture, and light winds, will continue to see IFR to low MVFR (localized LIFR) ceilings and visibility across western Washington this morning. Expect increasing southerly low- level winds later this morning ahead of the approaching front, and this should provide enough mixing to bring ceilings lifting to VFR across the region late morning or early afternoon. However, this will be short-lived as ceilings again lower to MVFR tonight as the next front moves through and brings steady rain. Breezy surface winds this evening, especially near the coast and the eastern Strait of Juan de Fuca/Admiralty Inlet. KSEA...We've lifted to VFR here this morning with ceilings around 5000 feet. Expect arrival of rain and lowering ceilings again after 03z tonight with MVFR cigs/visibility returning overnight Sunday night. && .MARINE...Winds have eased across the waters in between frontal systems this morning. Seas will continue to hover in the general 8 to 12 ft range through the next day or two, with a brief lull this morning expected. Otherwise, another round of stronger southerly winds will develop over the waters this afternoon and evening, with gusty southeasterly SCA strength winds expected across most zones (except for Puget Sound/Hood Canal). The likelihood of frequent or widespread gale gusts has decreased over the last 24 hours, which has lead to the gale watch being converted to a small craft advisory for most zones. The chances for more frequent gale gusts remains a little higher over the eastern Strait of Juan de Fuca, but even here is only around a 40% chance. Expect seas to sharply build over the coastal waters late Monday into Tuesday, as another large northwest swell from the Gulf of Alaska makes its way into the region. This will likely build seas into the 18-22 ft range early Tuesday. Furthermore, a stronger frontal system arrives later Tuesday with two impacts: first, chances for widespread gales remain considerably higher with this system than the earlier ones (60-80% chance across Eastern Strait of Juan de Fuca and coastal zones, and even a 40% chance for Puget Sound), and second, seas will again build above 15 ft, this time with a mix of southerly short period contribution and longer period west swell. Marine conditions remain very active through the week ahead as yet another disturbances is expected to reach the waters later in the week. Cullen && .HYDROLOGY...A more significant chance of precipitation is expected today 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 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 10 PM PST this evening 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 from 1 PM this afternoon to 2 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. && $$