A windy, winter storm packing heavy snow started moving into the Sierra Thursday, closing schools at Lake Tahoe, prompting a backcountry avalanche warning and snarling traffic on Interstate 80 west of Reno.
A winter storm warning remains in effect through 4 a.m. Friday from south of Yosemite National Park to about 200 miles north of Reno and Lake Tahoe.
More than a foot of snow is expected around the lake by Friday, with up to 30 inches above 7,000 feet, where winds could gust in excess of 100 mph, the National Weather Service said.
"The combination of heavy snow and wind will bring periods of whiteout conditions," the service said.
The storm out of the Pacific Ocean roared ashore in Northern California early Thursday, bringing heavy rain that snarled the morning commute and prompted flood advisories in the San Francisco Bay Area and south into the Central Coast.
Wind speeds reached 40 mph, with an isolated gust of 50 mph reported in the Marin Coastal Range, the National Weather Service office in San Francisco said.
"We've seen periodic traffic interruptions and accidents that California Highway Patrol have shared, so it's definitely a very hazardous, perilous condition up in the higher terrain as far as across western Nevada, including Lake Reno and Carson City," said Dustin Norman, senior meteorologist with the National Weather Service. "Friday may be a decent day for traveling in the higher elevations, but come Saturday through really most of Monday, it's going to be another round of treacherous mountain travel. So we don't want people to let their guard down after tonight. If they're planning on going in the mountains this weekend, they should make sure that they're prepared for winter travel."
Forecasters said much of interior Northern California could experience freezing temperatures early Friday.
At Lake Tahoe, all schools were closed Thursday on the north shore at Incline Village and the south shore at South Lake Tahoe.
Westbound traffic on I-80 was being held at the California-Nevada state line on the west edge of Reno at midday while crews worked to clear a jackknifed semi-trailer truck that was blocking the slippery travel lanes, the California Highway Patrol said.
Otherwise, chains were required on all but four-wheel-drive vehicles with snow tires on a 43-mile stretch of the interstate over the top of the Sierra north of Tahoe between Gold Run and Truckee.
The service said the heaviest snow — at times at rates of 2 to 4 inches an hour — was expected Thursday afternoon. About 8 inches of snow already was reported north of Reno at Susanville, where a weather spotter reported that 6 inches fell over about two hours.
The Sierra Avalanche Center in Truckee issued a backcountry avalanche warning through Friday for the Central Sierra Nevada, including the Tahoe area.
"Feet of new snow and strong winds will overload an already weak snowpack and result in very dangerous avalanche conditions in the mountains," the center said Thursday.
Christopher Weber of The Associated Press in Los Angeles contributed to this report.
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