Blizzard conditions continued to slam Northern California over the weekend with damaging winds and heavy snow dumping on mountain ridges down to the valleys.

Around 6.5 million people are under winter weather alerts across the Mountain West, with blizzard warnings still in effect for the Sierra Nevada.

The most extreme conditions are unfolding at the highest elevations in the mountains, with whiteout conditions and hurricane-force winds.

The snow has closed a 70-mile stretch of Interstate 80 near the Nevada state line for more than a day after highway officials reported stranded drivers Friday night.

“Extremely heavy snowfall rates of 2-6 inches an hour combined with very strong winds exceeding 100 mph at times will maintain impossible travel conditions in the Sierra Nevada,” the Weather Prediction Center said.

Officials added there is no estimated time for reopening.

The weather service has warned of “high to extreme” avalanche danger through Sunday afternoon in the Central Sierra and Greater Lake Tahoe area.

About 5-12 feet of snow was forecast to fall along the crest of the Sierra by late Sunday, while damaging wind gusts “possibly in excess of 75 mph” could be expected across the Intermountain West, according to the Weather Prediction Center.

“These winds will likely down trees and power lines, resulting in widespread power outages,” it said. “Moreover, cooler temperatures will usher into the West behind the initial front, lowering the snow levels down into many valleys.”

More than 13,000 homes and businesses were without power in California Sunday afternoon, down from nearly 40,000, according to the tracking website PowerOutage.us.

Numerous ski fields and chairlifts were also closed Saturday, including at Palisades Tahoe, Sierra at Tahoe and Mammoth, with some resorts warning of delayed starts on Sunday.

The ski resort Sierra-at-Tahoe in Twin Bridges shared images with CNN of snow piling up against the door of the resort’s maintenance shop and a car in the resort’s guest parking buried in snow that fell overnight.

“Winds will wane in intensity, though some additional heavy snowfall is expected through the day, particularly for the southern Cascades/Sierra, Wasatch, and central Rockies,” the National Weather Service said in its forecast discussion early Sunday.

The storm will begin to wind down later on Sunday, but will be followed by a new system on Monday, the weather service said.

Whiteouts and ‘impossible’ travel conditions

Extreme snowfall and roaring winds in the Sierra and parts of the northern ranges mean blowing snow and whiteout conditions making travel “impossible,” the National Weather Service warned.

The storm forced the closure of the main road to Mammoth Mountain ski resort, US 395, for hours Saturday due to whiteout conditions, according to the California Department of Transportation.

The snowy and windy conditions left some vehicles stuck on the road on Friday, with some motorists in need of rescue, according to the highway patrol office Truckee, which reported a “mass amount of vehicles stuck over Donner Summit.”

“At one point, emergency personnel and tow trucks had a difficult time getting to motorists due to blizzard conditions,” the agency said.

Many other roadways in the area are closed due to the weather and some are being chain controlled, requiring vehicles to have chains to proceed on the roadways.

The California Highway Patrol posted a photo Saturday afternoon of one of its cars stuck in snow. “Even our officers sometimes get stuck in the snow! The blizzard-like conditions have yet to let up, but nonetheless, our officers are working hard to keep everyone safe. Avoid travel during this time and stay updated on road conditions,” it said on Facebook.

On Sunday morning, the highway patrol in Truckee shared video of snowy conditions and low visibility on a stretch of I-80, which remained closed on Sunday at Colfax and the Nevada state line as of 6 a.m. Pacific Time.

Officials said there is no estimated time for reopening.

Yosemite National Park, which closed Friday due to the storm, will partially reopen to visitors on Sunday afternoon, park officials announced on Facebook.

“Expect snowy conditions throughout the park,” park officials said.

Park officials warned visitors tire chains may be required for their vehicles and to check road conditions.

A blizzard warning remains in effect for the park area until 7 p.m. on Sunday, according to the National Weather Service in Hanford, California.