PORTLAND, Ore. – The season’s first blast of arctic air will combine with an approaching Pacific storm to bring a wintry mix of heavy snow, freezing rain, ferocious wind and dangerously cold wind chills to parts of the Pacific Northwest this week.
While temperatures were in the upper 30s to lower 40s on Thursday morning, an arctic front carrying the coldest air of winter so far is dropping south out of British Columbia in Canada, which will cause temperatures to drop through the day from north to south from Washington into Oregon.
Temperatures are expected to drop to freezing in Seattle by mid-afternoon, then into the 20s by late evening.
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The passing frontal boundary may bring a brief period of snow across some areas of western Washington on Thursday, but only light accumulations are expected.
As cold air settles in Thursday night with lows in the 20s, a storm will approach Oregon from the Pacific Ocean on Friday, carrying a batch of moisture poised to wreak havoc as it collides with the subfreezing temperatures.
After days of computer forecast model uncertainty that showed the storm’s landfall anywhere between northwestern Washington and central Oregon, a more southerly track is now favored, with moisture arriving Friday evening into Saturday morning. The latest guidance suggests the Seattle area will no longer see much, if any, snow; instead, the storm will aim its wintry onslaught at northwestern Oregon.
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Precipitation will begin as snow, but with the storm coming off the relatively mild Pacific Ocean, a warm layer of air will likely change the precipitation to freezing rain along the north and central Oregon coast, spreading the threat inland to an area between roughly Eugene and Salem. The Portland and Vancouver metro areas will likely stay as snow, threatening the Friday evening commute and lasting into Saturday morning.
Winter Storm Watches are now in effect to cover a wintry mix for northwestern Oregon and into southwestern Washington, including the Portland and Willamette Valley area. Freezing rain could lead to ice accretions of up to a quarter-inch along the Oregon coast and southern Willamette Valley as winds gust to 30-35 mph. Snowfall totals still have quite a range from light to heavy due to remaining uncertainty in the storm track and strength, but there is a potential to reach 4 inches or more in the Portland area at the high end of the forecast.
Meanwhile, strong winds are expected near and along gaps of the Cascades, where arctic high pressure will be pushing icy gusts toward the Interstate 5 corridor. Along the Columbia Gorge, easterly winds could reach 50-60 mph with higher gusts, creating potential blizzard conditions during snowy periods. Up in northwestern Washington, while it’ll be dry, strong northeasterly winds roaring out the Fraser River Valley will drop wind chills to -15 degrees around Bellingham.
WHAT DOES THE WIND CHILL MEAN?
Meanwhile, east of the Cascades, temperatures will drop even farther as the arctic air mass settles in. Wind Chill Watches cover parts of eastern Washington and Idaho, including the Spokane, Washington, area, as strong winds drop wind chills as low as -25 to -35 degrees from Friday through the weekend with snow totals of 2-5 inches.
Winter Storm Watches and Warnings cover eastern Oregon as well for periods of heavy snow and gusty winds up to 45-50 mph.