The latest in an onslaught of winter storms comes with blizzard warnings for the Sierra Nevada and a new round of flooding for Northern California river towns where thousands of people remained under evacuation advisory Tuesday.
Forecasters warned of up to 10 feet of snow in the highest mountains, with up to 7 feet of snow around the resorts of Lake Tahoe, high risk of avalanches, and wind gusts to 60 mph. The Sierra ridge had gusts of more than 100 mph.
A blizzard warning is in effect for parts of the Sierra, a rarity and the first issued in the past nine years, said Scott McGuire, a forecaster for the National Weather Service based in Reno, Nevada.
"This is definitely a dangerous, life-threatening situation going on up there," he said Tuesday. "People should not attempt to travel at all."
Many ski resorts shut down Tuesday because of the dangerous storm. A number of main roads in the Sierra were closed, including Interstate 80, or required chains.
Nearly 3 feet of new snow already was reported Tuesday morning at the top of the Mount Rose ski resort between Reno and Lake Tahoe. A series of storms already has added 33 billion gallons of water to Lake Tahoe since Jan. 1.
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 fell for hours Tuesday in Northern California areas already 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.
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In Northern California's wine region, authorities expected the Russian River to rise 6 feet above flood stage by Wednesday after it spilled out of its banks over the weekend, flooding vineyards and riverside resorts and mobile-home parks.
Parts of 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."
After a storm-swollen river forced closing over the weekend, Yosemite National Park reopened the valley floor to visitors Tuesday morning, park spokesman Scott Gediman said.
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. The avalanche risk for most of Colorado's mountains is expected to remain high through at least Wednesday.