Winter Weather Advisories Take Effect as Early Snow Hits Northwest Mountain Passes

A colder Pacific weather system descending along the British Columbia coastline is delivering the season's first significant snowfall across the Pacific Northwest this week. The National Weather Service placed the Cascade Mountains under a winter weather advisory from Tuesday evening through Wednesday evening, prompting highway alerts as plunging snow levels threaten to create hazardous travel conditions across major regional passes.

Forecasts for the Cascades show snow levels falling from approximately 4,000 to 4,500 feet down toward 3,000 to 3,500 feet as cold air surges into western Washington. Total accumulations are projected to vary across the mountains, with forecasts ranging from 3 to 12 inches at elevations above 4,000 feet, or generally between 4 and 8 inches above the snow line. Higher highways such as those through Stevens Pass on U.S. Route 2 and White Pass are preparing for snow on the pavement for the first time this fall. Snoqualmie Pass along Interstate 90 is expected to see a few inches of slushy accumulation, with snowflakes possibly sticking to roadways through Wednesday night and Thursday.

Forecasters noted that the banded and showery nature of the precipitation means snowfall amounts could shift dramatically over short distances, with isolated heavier bursts exceeding official estimates. In the Olympic Mountains, a few inches of accumulation are anticipated around Hurricane Ridge. Lower elevations around Puget Sound and western Washington face gusty winds reaching 20 to 25 mph, overnight rain downpours, and afternoon conditions that may include small hail, ice pellets, and isolated lightning strikes alongside daytime highs lingering in the low 50s.

In response to the shifting weather, Washington State Department of Transportation crews are deploying to treat and clear mountain pass highways. Transportation officials and the National Weather Service are advising motorists to slow down, verify current road conditions via travel apps or by calling 511, and prepare their vehicles for winter driving. Recommended safety precautions include carrying emergency travel kits, packing appropriate supplies, and sharing transit itineraries with family before departing.

Unsettled weather is expected to linger across western Washington through Thursday and Friday, maintaining periodic mountain snow showers while lowland temperatures remain in the lower 50s. Although showers are projected to slowly decrease heading into the weekend, meteorologists caution that spotty rain may still disrupt outdoor activities such as trick-or-treating on Saturday evening, followed by drier and chillier conditions with morning lows dropping into the upper 30s.

Further inland, southwest Idaho is experiencing a brief reprieve before another storm system arrives in time for the weekend. After a chilly midweek featuring areas of morning valley fog, freezing temperatures, and daytime highs in the 40s and 50s, rain chances are slated to rise on Friday and peak Saturday evening. A passing cold front will generate widespread rain with a 50 to 80 percent chance of precipitation during prime trick-or-treating hours, keeping snow levels elevated between 6,000 and 8,000 feet before cooler air drops snow levels to 4,500 to 6,500 feet on Sunday. High mountain peaks above 6,500 feet in Idaho could pick up between 2 and 5 inches of snow, with isolated peaks reaching 7 inches.

In eastern Oregon, early winter conditions have already made an appearance. Anthony Lakes Mountain Resort in the Elkhorn Mountains northwest of Baker City reported new snowfall adding to several inches accumulated earlier in the week, with the National Weather Service forecasting a chance of light snow across the area over the coming days ahead of the resort's planned December opening.