796 FXUS66 KSEW 302236 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 236 PM PST Tue Dec 30 2025 .SYNOPSIS... Dry weather will continue with high pressure in place through Wednesday. Some areas that remain clear next couple mornings will continue to have the potential to see areas of fog. The new year will bring a return to active weather for western Washington, with a series of systems passing through into early next week producing light to moderate amounts of precipitation. High tides will also increase the risk of coastal flooding by Friday. && .SHORT TERM /TONIGHT THROUGH THURSDAY/... Upper level analysis shows a negatively tilted ridge from the four corners region of the U.S. up into the Pacific Northwest. Satellite has cleared up some from this morning with a mix of high clouds and sun continuing through the rest of today. There remains a corridor of patchy fog in the Chehalis-Olympia- Lakewood corridor as of late this morning. Model guidance still have the fog in this corridor lingering through early this afternoon (though there is still a strong likelihood of mist hanging around through the evening). Highs this afternoon will reach the mid to upper 40s (few 50s on the Cascades slopes and along the coast), and winds becoming light out of the south through tonight/tomorrow. Lows tonight will likely drop to around freezing, with a few sub 30s in the south interior (cloud coverage is expected to be similar to this morning with a mix of high clouds). The upper level ridge pattern will hold into Wednesday. Another round of fog appears likely in the morning. Main caveats are: how much of the cloud coverage tonight will hinder development, and how strong the temperature inversion will be for holding surface moisture in. The forecast soundings show a significant inversion with warmer air aloft Wednesday morning. The highest probabilities for seeing visibilities less than 1/2 a mile are the south Puget Sound/Kitsap and Chehalis Valley areas. This lessens to a 10-15% for the rest of the forecast area. The risk of air stagnation remains low, although a few areas may see locally degraded air quality with the strong inversion overhead. The remainder of Wednesday is dry to wrap up 2025 with fewer clouds going into the afternoon. Temperatures will be similar to Tuesday. By new years day (Thursday), the ridge will begin to broaden and weaken as an embedded shortwave impulse traverses the WA/OR coastline Thursday into Friday. A weak surface system with this impulse will move through Thursday into Friday. The southern 4/5ths of the forecast area (excluding the NW interior coast) will have a 30-50% chance of showers through the day, with chances increasing regionwide through the evening. QPF Thursday is expected to remain light (few hundredths), with snow levels remaining around 4,000-5,000 ft. Winds Thursday will remain light. High temperatures remain steady (from Tuesday/Wednesday) with overnight temperatures Thursday night warming into the upper 30s/low 40s. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... The weak impulse Friday will be replaced by a more broader shortwave trough moving up the WA/OR coast, passing through the region into the weekend. This will increase precipitation chances up to a 70-90% chance regionwide the later part of Friday into Saturday, decreasing into Sunday. Snow levels with this shortwave will drop from 5,000-6,000 ft down to around 3,000 ft through the weekend. The total amount of liquid water (QPF) coming from this system through the weekend remains light overall, with most likely the lowlands seeing around half an inch of rain, and the Cascades/coast seeing anywhere from around an inch to two inches. The Olympics have a slight chance of seeing heavier amounts of QPF upwards of 2-4". Much of the QPF in the mountains will turn to snow late Saturday into Sunday as the snow levels drop. The recent forecast package saw a downward trend in snow accumulations in Snoqualmie/Stevens passes (due to the delay in the snow level drops). The bulk of the snow accumulations remains the north Cascades and Olympics, with the best chance of advisory amounts of snow (greater than 6"). Breezy winds appear likely with the system Saturday night into Sunday, with most likely wind gusts in the 25-35 mph range (there is a 10% chance of gusts over 45 mph for the interior, and a 10% chance of gusts over 55 mph along the coast). The ensembles keep the progressive pattern going into the next week with all members showing a cool/wet pattern returning into the region. Its worth mentioning that the moist conveyor belt remains to the south in California next week (responsible for producing a lot of the atmospheric river conditions this month across the west coast). Temperatures in this period will hover in the upper 40s for highs, and upper 30s for lows. Additionally, astronomically large tides will increase the risk of minor coastal flooding, beginning Friday and lasting through the weekend. As confidence increases regarding the strength/track of the system as well as waves/winds, additional details regarding impacts will be shared. HPR && .AVIATION... An upper level ridge pattern will remain over the terminals rest of today into Wednesday. Flow aloft will weaken out of the southwest. Satellite this afternoon shows a pocket of fog slowly eroding in the Chehalis Valley (terminals continue to report LIFR conditions with 2 SM mist and low stratus). A pocket of low stratus clouds continues to produce locally MVFR conditions along the Strait of Juan de Fuca. Remaining terminals outside of this area are reporting VFR conditions, with high clouds and light NE winds 3-6 kt. Winds will decrease tonight to under 5 kt out of the south, becoming calm in some spots. Cloud coverage will remain about 50/50 through tonight/Wednesday. Warm air advection aloft will make the atmosphere stable going into tonight/Wednesday. This concerns the potential for fog Wednesday morning (especially with a strong inversion despite the partial cloud coverage). The highest chance of seeing fog remains the south interior (up through south Puget Sound/Kitsap) through most of tonight with most models showing a surge of fog moving up into the Seattle area between 14-18Z. Another area of fog is likely to develop in the Everett-Mt. Vernon corridor tonight/tomorrow morning. Clearing will take place late Wednesday morning/afternoon, with VFR conditions/high clouds rest of Wednesday. Winds will remain light out of the south Wednesday. KSEA...VFR through tonight. Fog to the south will develop overnight, and push towards the terminal around sunrise Wednesday morning. The highest chance for fog in the terminal is from 14-18Z, with a 30-40% chance of visibilities less than 0.5 SM during this window. Once the fog clears, VFR conditions are expected for the remainder of Wednesday. NE winds 4-6 kt will shift to the south later this evening, becoming less than 5 kt tonight/Wednesday. HPR && .MARINE... A ridge/high pressure pattern over the waters will keep conditions quiet/calm through the end of the week. A thermal trough also remains in place through the first half of the week, keeping the flow offshore. The pattern remains favorable for the development of areas of patchy to locally dense fog over portions of the interior waters Wednesday and Thursday mornings. The seas through Friday will hold around 6-8 ft. A weak disturbance will pass over the waters Thursday/Friday, with a stronger system passing through late Friday through Sunday. A period of breezy south winds of 20-25 kt appears likely Saturday/Sunday over the coastal waters and Strait of Juan de Fuca. Seas will also increase to 14-16 ft Saturday with this system, then decrease to 6-8 ft Sunday through early next week. HPR && .HYDROLOGY... Precipitation will return Thursday through early next week, which may cause small rises in rivers, creeks and streams. No rivers are currently forecasted to flood at this time, however the Skokomish River is expected to rise above action stage with the precipitation falling this weekend. HPR && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$