FXUS66 KSEW 191644 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 844 AM PST Wed Feb 19 2025 .UPDATE...A frontal system continues to move across Western Washington this morning for widespread lowland rain and mountain snowfall. Given the increased snowfall amounts in the forecast for the central Cascades, have issued a Winter Weather Advisory though early Thursday morning, including both Stevens and Snoqualmie Pass. The bulk of the snow accumulation is expected later this afternoon into tonight as winds transition more westerly. Generally 5 to 8 inches of snow is expected, with the higher amounts at Stevens Pass. Otherwise, the forecast is on track. && .SYNOPSIS...A warm front will continue to advance across western Washington today, with lowland rain and mountain snow continuing ahead of a trailing cold front. A weak upper ridge will build into the region Thursday, but will only be a brief break as the region will again see another series of fronts approach Friday. An atmospheric river looks to move into western Washington over the weekend, bringing heavy rain to the area into early next week. && .SHORT TERM /TODAY THROUGH FRIDAY/...The next weather system is already pushing into the region with the leading warm front lifting across the region, spreading widespread rainfall and some mountain snow into the Cascades. Snow levels may rise just a bit in the warm sector before the trailing cold front, in the process of occluding, makes its way across Western Washington late today. Expect continued lowland rain and mountain snow above around 3500 ft through the day, with snow levels rising closer to 4500 ft in spots. Light easterly winds near Snoqualmie maintain a low (10%) likelihood of freezing rain, but thermal profile looks marginal and suggests the precipitation may fall mostly as snow. Most likely snow amounts remain around 5-6 inches for the central Cascades (including Stevens and Snoqualmie passes) with higher amounts in the southern zones (including Paradise and White Pass). It's worth noting that the "high-end" snow amounts for the central Cascades have increased a little bit owing to heavier focused precipitation late tonight behind the cold front. So, while the forecast hasn't changed (nor has the current winter weather advisory), will need to continue to evaluate the threat and any potential need to expand the advisory northward. Showers will then taper by late Thursday morning as a weak upper level high pressure moves back over the area. This upper ridge will give a break in the action for most, but some light precipitation remains possible closer to the coast and the far northern areas as the leading warm front associated with the next system isn't too far behind. For most though, a drier day with temperatures in the upper 40s to lower 50s. Another cold front sweeps across the region on Friday as it falls apart. This will bring much more modest precipitation amounts with up to around a tenth of an inch of rain for most (locally higher to around half an inch along the coast), and another light snow accumulation down to around 4000 ft. This will just be setting the stage for the weekend, however. .LONG TERM /SATURDAY THROUGH TUESDAY/...The weekend looks to be rather wet across the region with an atmospheric river setting up near the region Saturday and over the area into the first part of next week. The rainfall amounts remain fairly similar to the previous forecast and remain in line with a slightly wetter shift in the probabilistic guidance this cycle. With a fairly mild air mass over the region and snow levels climbing to 6000 ft or higher on Saturday, expect much of this precipitation to fall in liquid form. This will enhance the risk of seeing areas rivers rise closer to flood stage - see the HYDROLOGY section for additional details regarding this threat. The pattern looks to remain active with another disturbance crossing the region by Tuesday, though at least it appears a bit more fast-moving which will limit impacts. && .AVIATION...South to southwest flow aloft will veer westerly later today as an upper level trough and associated frontal system move onshore. VFR ceilings early will deteriorate to MVFR at times by late morning through this afternoon as rain continues to spread eastward across the area. Precipitation will decrease by late afternoon and evening behind the front, but a moist air mass will remain in place with ceilings consolidating into mostly MVFR. There may be a brief rise into VFR early this evening before returning to high-end MVFR. Gusty southerly surface winds are expected to develop across the interior by early afternoon and persist through the evening before gradually easing overnight. KSEA...VFR ceilings in light rain are expected to gradually lower to MVFR by late this morning just ahead of an occluded front. Precipitation is expected to diminish after 00Z with ceilings in the higher range of MVFR persisting into tonight. There may be a brief rise in ceilings above 3000 ft between around 03-09Z Thursday before returning to high MVFR. Surface winds E/SE 8 to 12 knots shifting southerly with the arrival of the front and increasing to 15 to 25 knots at times mid-afternoon through the evening before gradually easing. 27/LH && .MARINE...Gales over much of the coastal waters will transition to small craft advisory conditions in the wake of an occluded front that will move onshore around midday. Have extended the Gale Warning over the outer coastal waters for lingering gusts behind the frontal passage into this afternoon. Surface high pressure rebuilding behind the front will lead to a punch of westerlies through the Strait of Juan de Fuca as well as an increase in southerlies through Puget Sound through Admiralty Inlet into the Northern Interior Waters this afternoon and evening. Surface ridging over the coastal waters tonight will shift inland on Thursday as another warm front lifts northward across the offshore and coastal waters. A series of systems will impact the waters Friday through the weekend likely necessitating additional headlines for wind and/or seas across much of the area waters. Seas 10 to 15 ft today and tonight. Dominant periods of around 10 seconds are making for very choppy seas. Seas may briefly subside to around 8 to 9 ft on Thursday (with dominant period increasing to around 14-15 sec) before becoming hazardous once again during an active time expected Friday through weekend. 27/LH && .HYDROLOGY...An active pattern will bring a series of frontal systems across the region this week. With snow levels generally around 3000 feet, expect some rises on rivers (especially the Skokomish) but river flooding is not expected through Friday. The additional moisture, however, could set the stage for a more hydrologically notable event by the weekend. The potential arrival of an atmospheric river this weekend into early next week would have the potential to push rivers even higher, opening the door to the potential for flooding by the early portion of next week. It is increasingly likely that snow levels will climb into the 6000 ft or higher range this weekend as a mild and moist weather system takes aim at the region. While there remains some uncertainty with respect to the location of heaviest rainfall, there's a high likelihood (greater than 70% chance) of 3 to 4 inches of rain across the mountains. With around a 40% chance of seeing a 5+ inch total in the favored locations of the Olympics and the central Cascades, will need to closely monitor the precipitation forecasts heading into the weekend. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...Winter Weather Advisory until 4 AM PST Thursday for West Slopes North Central Cascades and Passes-West Slopes South Central Cascades and Passes. PZ...Small Craft Advisory until 2 AM PST Thursday for Grays Harbor Bar. Small Craft Advisory until 10 PM PST this evening for Admiralty Inlet-Central U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal-West Entrance U.S. Waters Strait Of Juan De Fuca. Gale Warning until 10 PM PST this evening for East Entrance U.S. Waters Strait Of Juan De Fuca. Gale Warning until 10 AM PST this morning for Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm. Small Craft Advisory until 4 AM PST Thursday for Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm. Small Craft Advisory until 4 AM PST Thursday for Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm. Gale Warning until 1 PM PST this afternoon for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm- Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. Small Craft Advisory from 1 PM this afternoon to 4 AM PST Thursday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. && $$