The Seattle-Tacoma area was said to be near certain to see 1 ½ to 3 inches of snow this weekend, with an even chance of accumulations reaching 5 to 6 inches, and a small chance of 8 inches, according to the National Weather Service.

That might be dropping a bit, or coming a bit later than expected.

Yes, snow already was falling in spots Saturday morning where it was just cold enough. Lacey, for instance, and Bothell, among other places. And a slushy preview arrived late Friday, bringing hope to those enamored of the thought of a white Christmas and trepidation to those needing to make a long drive for holiday celebrations.

With a high in the upper 30s expected Saturday, accumulation during the day has largely never been in the cards. Late Saturday, when temperatures dip into the 20s, and on Sunday — that has been the focus.

Snow is likely to accumulate Sunday, as the weather service says snow showers are likely in the morning and afternoon, with 1 to 2 inches of snow piling up. The highs aren’t expected to go above 30, and north and northwest winds will keep it chilly.

Next week, temperatures will dip as low as 18 degrees, the lowest in several years.

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Communities farther north, in some cases still recovering from floods, will be hit sooner and harder this weekend. A winter storm warning started Saturday morning for the Bellingham, Nooksack Valley and Skagit Valley areas, Whidbey and San Juan islands, and north Olympic Peninsula, where gusts of up to 40 mph are expected, along with 3 to 11 inches of weekend snow.

Snohomish County was forecast to possibly receive a half-inch of snow early Saturday, then rain, then snow Saturday night. Highs will reach only 30 degrees Sunday with wind chill factors of 16 to 20 degrees.

The severe weather is caused by frigid blasts from Canada’s Fraser River Valley swooping from the north toward Puget Sound, ready to collide with ocean moisture coming from the west, to produce a white Christmas in the late hours of the holiday.

“There’s a complicated dance going on, and it makes it challenging to forecast, because everything has to line up right for snow in the lowlands,” Kirby Cook, a National Weather Service science and operations officer, said Friday evening. “To get snow in the Seattle area, the cold air has to get here before the precipitation stops.”

On the Pacific coast, a similar burst of frosty air will push west through the Columbia River Gorge, bringing an extreme 10 to 20 inches to Cape Disappointment, Long Beach, Willapa Bay and Astoria, Oregon, with snowdrifts expected during 35 mph gusts, according to the weather service. A winter storm warning, already in effect, is to run until 4 a.m. Monday.

Some cities have opened warming shelters to provide hundreds of spaces to aid homeless people or anyone lacking heat. Snohomish County sites are in Everett, Snohomish, Monroe and Lynnwood, mapped here. Day and overnight warming shelters throughout King County are listed here.

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Seattle Mayor Jenny Durkan issued an emergency proclamation Friday. The city has encouraged daytime stops at Seattle Center Armory, and announced two overnight warming shelters beginning at 7 p.m. Saturday: for 100 people and leashed pets at Seattle Center Exhibition Hall; for 80 people and service animals only at Compass Center, 210 Alaskan Way South in Pioneer Square.

To assure staffing, Durkan announced bonus payments of $150 or $250 to city employees and contractors who staff warming centers and services this holiday.

Seattle Department of Transportation workers were making test runs Friday on salt and snowplow routes, following similar practice trips Dec. 9. SDOT was largely successful in keeping main road and bus routes passable within hours of 2019 and 2021 snowstorms, though many sidewalks stayed icy. SDOT’s snow routes and real-time response map are here.

Highways across Snoqualmie and Stevens passes were covered in snow and slush Friday night, with chains required, except on all-wheel drive vehicles.

By Sunday, when thousands are driving home from holiday trips, Snoqualmie Pass is expected to reach a high of only 19 degrees, and a low of 4 degrees Sunday night under calm winds, the weather service predicts. A foot or more of snow could fall before then.

Traffic congestion Sunday is predicted to be stop-and-go from noon to 5 p.m. returning west from Cle Elum to North Bend, and not full speed until 7 p.m., based on historical patterns that could change in heavy snow.