More storms with rain, mountain snow lining up for northwestern US

The Pacific winter storm season is already well underway with two more storms set to pivot ashore in the western United States into next week. Snow levels will dip enough to bring wintry travel to many of the passes from Washington to Northern California, AccuWeather meteorologists say.

Soon after the last snow showers and spotty freezing drizzle shut off over the Cascades and Sierra Nevada on Friday, the next storm will roll ashore following several hours of dry weather and even some sunshine on Saturday. Snow from the most recent storm will continue to progress over the interior West, with up to half a foot expected over the ridges of the Nevada mountains, Wassatch, Bitterroots, Clearwater and Bighorns into Saturday night.

The next storm in the series will move ashore this weekend in the Northwest.

Snow levels with the weekend storm will vary, with some snow initially for the Cascade passes from later Saturday to Saturday night, followed by some rain or a mixture of rain and snow on Sunday, before colder air arrives at the tail end of the weekend.

"Snow levels will crash over the Cascades from Sunday night to Monday," AccuWeather Senior Meteorologist Dan Pydynowski said, "Snow levels could be as low as 1,500-2,000 feet by Monday, which is low enough that travel over the Cascade passes from Sunday night to Monday are adversely affected."

"A foot or more of snow may pile up at pass level in the Cascades from Sunday night to Monday night," Pydynowski added. "The snow can come down at a fast enough pace to temporarily close the passes, and winter tire chains will be a necessity for travel."

The storm from later Saturday to Monday will bring rounds of drenching rain to the Interstate 5 corridor in Washington and Oregon. Snow may even make for slushy conditions over some of the adjacent hilly areas by Monday. Low cloud ceilings and stiff breezes can lead to airline delays.

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Farther south, only a limited amount of moisture will be available in Northern California beyond that of the Coast Ranges, Siskiyous and Sierra Nevada. Conditions may become slippery over the higher ground along I-5 in Northern California and I-80 over Donner Pass from Sunday night to Monday.

Another storm will follow from Tuesday night to Thursday of next week.

The storm may be larger and more potent than the storm this weekend. A period of heavy snow may occur during the first part of the storm at midweek in the Cascades, prior to a surge of warm air with rain, then a return of cold air with snow showers over the passes. Strong winds will create large waves offshore and along the Washington and Oregon coasts and can lead to sporadic power outages in coastal and mountainous areas.

"There is the potential for an atmospheric river event with the midweek storm in the Northwest," AccuWeather Senior Meteorologist Brett Anderson said. An atmospheric river is a long plume of moisture extending for miles across the ocean and onto land. Within this plume, a firehose effect of rain or snow can occur with major consequences.

If so, flooding rainfall could be directed at low-elevation areas along I-5 and bursts of exceptionally heavy snow over the high country in the Olympics and Cascades. The storm next week has the potential to trigger major travel problems on the roads and may trigger a significant number of flight cancellations in the Northwest.

"At the very least, this looks like a significant storm coming up next week for the Northwest with the potential for road closures due to rain and mudslides in lower elevations and various reasons over the passes," Pydynowski said.

"The same midweek storm has the potential to soak the San Francisco Bay area with perhaps the biggest rain of the season so far, depending if rain can settle farther south toward the end of next week," AccuWeather Senior Meteorologist Heather Zehr said.