(AP) — The latest in an onslaught of winter storms bore down on California Tuesday with what authorities warned was a life-threatening blizzard for the Sierra Nevada mountains and a new round of flooding for Northern California river towns where thousands of people remained under evacuation orders.

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Forecasters warned of up to 8 feet of snow in the highest mountains, with up to 5 feet of snow around the resorts of Lake Tahoe, high risk of avalanches, and wind gusts of over 50 miles an hour.

White-out conditions were possible, said Scott McGuire, a forecaster for the National Weather Service based in Reno, Nevada. Forecasters called conditions potentially deadly for drivers in the mountains.

“People need to avoid traveling if at all possible,” McGuire said.

Many ski resorts shut down Tuesday because of the dangerous storm. At Mammoth Mountain, one of the state’s southernmost big ski resorts, gales forced operators to close all but one ski lift. “We’ll open more if we can,” spokeswoman Joani Lynch said. “We have high winds and pretty heavy snowfall right now.”

Tuesday’s storm was the latest in days of back-to-back systems that have brought the heaviest rain in a decade to parts of Northern California and Nevada. The storms are part of an “atmospheric river” weather phenomenon that draws precipitation from the Pacific Ocean as far west as Hawaii. Its impact can be catastrophic for areas hit by the heaviest rain.

In Sacramento, workers with California’s Department of Water Resources opened a half-dozen century-old spill gates on the state’s biggest river, the Sacramento, before dawn Tuesday to ease pressure on the swollen river and on levees.

California is in a six-year drought, and the last time state workers had needed to open the gates and spill water into side channels was December 2005.

“They were a little bit rusty,” department spokesman Ted Thomas said, “but they were able to open them fine.”

Heavy rain were fell Tuesday for hours in areas of Northern California that were soaked by more than a foot of rain over a 72-hour period that ended early Monday, forcing hundreds to evacuate and leaving thousands without power.

The heavy rains forced rivers out of their banks and toppled trees, among them the famed “Pioneer Cabin” giant sequoia in Calaveras Big Trees State Park that had a drive-thru tunnel carved into its base more than a century ago.

In Northern California’s wine region, authorities expected the Russian River to rise 4 feet above flood stage Tuesday afternoon, after spilling out of its banks and flooding vineyards and riverside resorts and mobile-home parks over the weekend.

Parts of California’s wine country in Sonoma County were among the hardest hit, receiving up to 13 inches of rain from the weekend storms. Rolling hills and vineyards along the scenic route known as River Road were submerged with just the tips of the vines rising above flood water.

Melba Martinelli, who lives in the Russian River town of Guerneville, waded through her yard Monday in knee-high rain boots, surrounded by flooded streets.

“I’m watching the water come up higher and higher, and my boots are almost going underwater now,” Martinelli said. “The river is coming up the street now. It’s pretty scary.”

In the San Francisco Bay Area, a coastal flood advisory was in effect through Friday, with a forecast for up to 7-foot “king tides” that could pose a flooding risk for coastal roadways, said Steve Anderson, a National Weather Service forecaster in Monterey, California.

After closing over the weekend, Yosemite National Park planned to reopen the valley floor to visitors Tuesday morning after a storm-swollen river forced its closure through Monday, park spokesman Scott Gediman said.

Emergency workers in Nevada voluntarily evacuated about 1,300 people from 400 homes in a Reno neighborhood as the Truckee River overflowed and drainage ditches backed up.

In Colorado, snow and strong winds worked together to set off an avalanche up to 15 feet deep that closed Interstate 70 at Vail Pass in Colorado early Tuesday.

A tractor-trailer carrying mail was caught in the slide, but the driver wasn’t injured, the Colorado State Patrol reported.

The avalanche risk for most of Colorado’s mountains is expected to remain high through at least Wednesday.

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Gecker reported from San Francisco. Associated Press writers Ellen Knickmeyer in San Francisco, Christopher Weber in Los Angeles, Scott Sonner in Reno, Colleen Slevin in Denver and Scott Smith in Fresno also contributed to this report.