As in Sunday.
Two weather systems moving into Western Washington both have potential to bring accumulation snow to parts of the region - mostly from about Everett north and the Eastside foothills but everyone might at least see a little snow, especially with the second system Sunday afternoon through Sunday night.
A Winter Storm Watch is in effect from Saturday evening through Sunday night to cover both inbound weather systems.
Areas in the watch extend from essentially the King/Snohomish County line north to the Canadian border (including Lynnwood, Everett, Marysville, Mt. Vernon, Bellingham), the Hood Canal area, the north Sound Islands (San Juans, Camano, Whidbey) the northern Olympic Peninsula (Pt. Angeles, Sequim) and the North Coast (Forks). The Watch that had been in effect for the Eastside foothills has been canceled.
A "Watch" means there is potential, but not yet assured. Right now the watch is giving potential from 2-5 inches as an overall total by Sunday night.
Those left out of the watch area, which includes the Seattle/Bellevue and Tacoma Metro areas (and now the King/Pierce County foothills), as well as all points south are likely to remain too warm for heavy snows although areas may at least see some snow at times, with maybe 1" in the Seattle area (especially the hilltops) and 1-2" inches in the Cascade foothills north of I-90.
Dark blue shaded areas show locations under a Winter Storm Watch It remains a very tricky forecast as while moisture is present, there is still a challenge of deciphering how much cold air will be present to make it snow and how far south it will spread.
The cold air is dependent on arctic air that is building in the interior of British Columbia being drawn into Western Washington through the Fraser River Valley near Bellingham.
The BIG question is: How far does that cold air spread across Western Washington? There will be a distinct rain/snow line in our region this weekend, the challenge will be where it sets up, as obviously 30 miles either side of this line could have wildly different weather, with potential major impacts to those on the north side and major disappointment for those on the south side.
Our forecast models had been at a standoff as to where that line sets up -- one adamant snow covers much of Puget Sound region; the other it stays mainly Skagit County north and the rest of the region is just rain. But they are finally coming into better agreement, although there are still some pretty large differences in opinions in how cold it'll be and how much snow will fall.
Our forecast is thinking Everett is more likely the boundary between the cold/warm air (even the more aggressive model has now come to say that Seattle likely stays rain or just a dusting). The Winter Storm Watch is in effect to cover for potential for those areas being on the snow-side of the line, but especially as you head to the southern fringe of that watch area, potential increases for getting little to no snow if the snow line remains further north. Also note that the Hood Canal and northern Olympic Peninsula also have greater potential for snow due to proximity to the Olympic Mountains.
With that said, here we go:
This is the first system but it's not very cold yet. Still once we pass midnight, rain will change over to snow in the far North Sound with snow levels dropping to 0-200 feet across Whatcom and Skagit Counties, and 400 feet around Snohomish County and 500 feet across the north Olympic Peninsula. About 1" or so is possible here, 2" around Bellingham. Lows will be in the low-mid 30s. The rest of the area may see some slushy wet snow but no accumulations expected.
The wind increases out of the Fraser River Valley, helping to spill some colder air further across the North Sound region. Here is where that rain/snow line really comes into play.
There will be lingering rain/snow from Saturday night, and then a renewed threat of rain/snow for the afternoon and evening.
Forecast totals are for an additional 1-4" inches possible in the watch area and again further north you are, the better the chance for getting snow and the higher end of the forecast totals. Storm totals could reach 2-5" depending on what happened early Sunday morning. Highs will be in the low 30s near Bellingham, mid 30s across North Sound, Olympic Peninsula and Hood Canal, upper 30s/near 40 central Puget Sound area and foothills and low-mid 40s Tacoma south
What About Seattle and Tacoma?
For Seattle/Bellevue Metro area, this is really tough call, but is not looking good for snow fans. Forecast models are starting to come together and are leaning toward this area being south of the rain/snow line and being too warm to snow, aside from maybe the highest hilltops. But there is a chance the rain snow line may set up further south and bring accumulating snow.
From Tacoma south, your odds get even slimmer as you go south. Most likely rain for this area. Highs will be around 40 in Seattle and likely low 40s Tacoma south.
This will have to essentially be forecast in near real time so our best advice is to at least be prepared for a few inches of snow but understand confidence is not high that it will actually occur.
Snow/rain decreases Sunday night and we warm to where whatever showers are leftover Monday morning will be rain. It looks like Seattle, Bellevue and Tacoma's commute may be OK, but Everett and points north may have challenges.
Any more snow?
All areas should warm up by Monday morning and the forecast is for occasional rain showers the rest of the week as temperatures rise into the 40s.