Widespread rounds of mountain snow in California will continue through Thursday night, with additional pass closures. As yet more storms roll in from the Pacific, they will focus on the mountains of Northern California and expand over Oregon and Washington through nearly the end of February.
Pacific storms are lining up with mountain snow as their payload
A long train of storms stretches across much of the North Pacific.
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“When this pattern finally wraps up late next week, parts of the Sierra Nevada will end up with 12-16 feet of snow,” AccuWeather Chief On-Air Meteorologist Bernie Rayno said.
For a time on Monday, Interstate 80 over Donner Summit, California, was closed. As of Monday night, the highway had reopened, but with strict chain restrictions. Additional closures are possible through Thursday. Snowfall rates of 2 to perhaps 4 inches per hour can easily overwhelm road crews, leaving motorists stranded. As of around daybreak on Tuesday, there has been just under 3 feet of snow over Donner Pass from the storm, with heavier amounts likely over the high country.
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“Snow levels have dipped as far as about 1,500 feet in Northern California and will dip to about the same level in parts of Southern California Tuesday night to Wednesday,” Rayno said. “That means that wintry and slippery conditions will occur over the passes in Southern California along I-5 and I-15, not just along I-80.”
From Wednesday to Wednesday night, snow showers are in store for the mountains of California, with rain showers down near the coast and in the valleys.
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Another storm will pivot through California on Thursday and Thursday night with more bursts of heavy snow for the Siskiyous and Sierra Nevada in the northern and central parts of the state, as well as the various ranges in Southern California. In total, through Thursday night, from 1 to as much as 6 inches of snow can pile up over the Southern California passes, with up to a few feet of snow over the ridges and peaks.
“Along with the obvious problems from heavy rates of snow will be the potential for avalanches through the passes and in the high country,” AccuWeather Meteorologist Alyssa Glenny said. When snow rapidly accumulates on steep terrain, it can become unstable and give way without warning.
Rain to rise flash flood risk, increase mudslide potential
Rain and localized flooding are likely in the lowest elevations near the coast and in the valleys.
In the lower south- and west-facing hillsides of the Sierra Nevada and the Transverse Ranges, from 4-8 inches of rain in total is forecast with an AccuWeather Local StormMax™ of 9 inches. Both Los Angeles and San Francisco can expect a multiple-day storm total of 2-4 inches.
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Since the new rain year began on Oct. 1, downtown Los Angeles has received 16.66 inches of rain compared to a historical average of 9.12 inches through Feb. 16. This is nearly twice the average rainfall.
Enough rain has already fallen to lead to incidents of flash flooding and urban-style flooding at lower elevations in many major California cities, from San Francisco to Los Angeles and San Diego. Each subsequent storm through Thursday will raise the risk of mudslides and other debris flows. Hillsides made unstable by the rain could slip. Road washouts are possible.
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Storm track to shift to the north this weekend along Pacific coast
As that storm moves over the interior Southwest on Friday, a shift in the storm track will favor little to no rain and mountain snow in Southern California, as well as ongoing precipitation for Northern California and the Northwest starting later this weekend through much of next week.
Rounds of snow will occur across the Cascades in Oregon and Washington, as well as additional periods of snow for the Siskiyous and the northern Sierra Nevada in California.
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