SEATTLE – After a rare week-long break from rainy weather in the heart of November, storms are returning with a vengeance to the Pacific Northwest as a series of atmospheric river storms take aim at the region, threatening flooding rainfall and snow measured in multiple feet in the mountains.
The first storm pushing in off the Pacific Ocean later Thursday and into Friday will bring an initial round of typical autumn rain to the lowlands but pummel the Cascades and Olympics with heavy snow. A second storm right on its heels will keep the rain and mountain snow going into the weekend.
Winter Storm Warnings will go into effect early Friday morning, stretching along nearly the entire spine of the Cascades from Washington into southern Oregon, including all the heavily traveled mountain passes near the Seattle and Portland areas. The warnings span both initial storms and last into Sunday morning for up to 2-3 feet of snow, with the bulk of the snow falling from Friday night into Saturday. Blowing snow is likely as wind gusts reach 40-50 mph.
“For many of you that have kids going to university on the other side of the state, this is not going to be the weekend for them to travel home,” FOX Weather Meteorologist Britta Merwin said. “You’re going to want to tell them to just stay there and have a weekend with your friends instead of heading back home.”
Meanwhile, snow will spread out into eastern Washington and Oregon, with 2-4 inches of snow from Friday night into Saturday.
“Morning commutes across the region will be slick and more hazardous than normal,” the National Weather Service office in Spokane, Washington, wrote in its Wednesday night forecast discussion.
The pattern shifts on Sunday as the jet stream instead draws up a pair of warmer, tropically infused atmospheric river storms to push into the Pacific Northwest into next week.
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These storms will bring a sharp increase in both the snow levels and the amount of precipitation, switching the concerns from heavy snow to heavy rain and potential river and urban flooding.
Snow levels will rise to over 5,000-6,000 feet with the first atmospheric river on Sunday afternoon and Sunday night, with rain lasting into Monday.
Just hours later, a second, more robust atmospheric river is expected to tap into copious amounts of warm, tropical moisture near Hawaii, earning the storm the nickname as a “Pineapple Express” atmospheric river.
Snow levels will be over 7,000 feet by late Monday into Tuesday as several inches of rain fall – both in the populated lowlands and in the mountains. Some of the mountain areas could see as much as 10 inches of rain between the two atmospheric rivers, leading to flooding potential on multiple rivers across the region.
“Once we get into Sunday, Monday, Tuesday – this is where the concern is because now the snow levels go way up to 10,000 feet,” FOX Weather Meteorologist Craig Herrera said. “All of that fresh snow that’s fallen will be melting, and you’ll be talking about flooding – it’ll be a mess.”
The heavier rain tapers off to a cooler, showery pattern later next week.