Potent storm system to unleash late-season, long-duration snowstorm in Northwest U.S.

A potent storm system is forecast to slam into the Northwest U.S. this week, unleashing late-season snowfall, rain, and thunderstorms for the region. The long-duration snowstorm is set to develop along the northern Rockies and the Bitterroot Range Wednesday night, May 19, 2021.

Following the mainly dry start to the week, the storm system is forecast to barrel into the Northwest at midweek. A long-term snowstorm is set to develop with the potential to unleash heavy snow on parts of the northwest beginning Wednesday.

According to AccuWeather meteorologists, while snow this late in the season may happen at times, it will be quite unusual for an extensive area of the northern Rockies to be experiencing wintry weather conditions at this time of the year.

"A late-season, long-duration snowstorm will develop along the northern Rockies and the Bitterroot Range Wednesday night," said AccuWeather Storm Warning Meteorologist Michaela Heeren.

Showers and a few thunderstorms will strike the Pacific Northwest as the storm heads inland.

"By Wednesday night, this storm will be able to pull deep moisture all the way from the Gulf of Mexico into the northern Rockies," according to AccuWeather Meteorologist Mary Gilbert.

"This abundance of moisture means there will be plenty of fuel for lower elevation showers and thunderstorms, in addition to higher elevation snow."

Areas from Seattle and Spokane, Washington, to Portland and Eugene, Oregon, may see showers.

"As markedly colder air sinks southward out of Canada on Wednesday night, snow levels will begin to drop across the northern Rockies," Gilbert continued.

"Snow levels look to bottom out around 1 200 to 1 500 m (4 000 to 5 000 feet) on Thursday and Friday (May 20 and 21), meaning many of the major passes in the area, including Donner Summit, may be at risk for slushy or snowy road conditions."

"While wet weather could be perceived as an annoyance to some residents, any drop of rain or flake of snow will help in the fight against drought in the Northwest," Gilbert noted.

The National Weather Service warned the threat of severe thunderstorms will move to parts of the Northern and Central High Plains on Thursday. The boundary and weak onshore flow will generate rain and higher elevation snow over the Pacific Northwest into the Northern Rockies through Friday.

Featured image credit: Flickr