An avalanche in the Lake Tahoe region on Tuesday has left ten backcountry skiers missing amidst heavy snowfall.

The skiers, comprising four guides and twelve clients, were navigating the Castle Peak area of the Sierra Nevada near Truckee, California, when the avalanche occurred around 11:30 a.m., according to the Nevada County Sheriff’s Office.

The avalanche hit at an altitude of approximately 8,200 feet and was classified as a D2.5. This rating signifies a ‘large’ to ‘very large’ slide with the potential to bury or seriously harm individuals, as reported by the Sierra Avalanche Center.

While at least six skiers managed to survive the incident, they remained stranded on Tuesday afternoon, following instructions from authorities to stay put. Meanwhile, the other ten skiers remain missing.

Close to 50 first responders have been deployed to the area to assist the survivors and locate the missing individuals. Additionally, a SnoCat team has been mobilized to aid in the search and rescue operations.

The group of skiers had arrived at the Sierra Nevada on Sunday, with plans to leave on Tuesday from the Frog Lake Huts, a backcountry lodge managed by the Truckee Donner Land Trust, as explained by Steve Reynaud, an avalanche forecaster at the Sierra Avalanche Center, to the Press-Democrat.

The land trust notes on its website that usual routes to and from the lodge have ‘some degree of avalanche hazard,’ and Reynaud said it appeared the group was heading toward the Castle Peak trailhead near the Boreal ski area, next to Interstate-80.

That trek, he said, passes through ‘numerous avalanche hazards.’

‘An avalanche burying seven to 10 people would be a very large avalanche, or a group being in a bad location, or potentially both,’ Reynaud said.  

Nearly 50 first responders are scouring the area of the Sierra Nevada’s Castle Peak area near Truckee, California to find six skiers who survived an avalanche – and 10 people who remain unaccounted for

The remote location and treacherous weather conditions have hindered the search efforts

Travel in, near, or below the avalanche terrain in the backcountry was strongly discouraged

It is likely that the group carried snow probes and shovels to be prepared in case of an avalanche, Reynaud suggested.

Still, he said, ‘As soon as you have more than one person or multiple people buried, it becomes a much more difficult rescue.’ 

If a buried person is not dug out within 10 to 15 minutes, ‘survival drops off pretty quickly.’ 

Making matters worse, the Nevada County Sheriff’s Office warned that conditions remain ‘highly dangerous,’ with an avalanche warning remaining in effect through Wednesday as the rapidly accumulating snowfall piled onto already fragile snowpack layers amid gale-force winds.

The remoteness of the site where the group is stranded has also hampered the official rescue response, Reynaud said.

‘There’s not an easy way for search and rescue or outside help to get there,’ he said. ‘Even getting rescue personnel to the location to start with has been a major challenge.

‘With the weather right now, conditions are not just dangerous, but hard to get around in the backcountry with all this new snow and wind,’ Reynaud said, adding that the dangerous conditions have made a helicopter rescue impossible.  

Interstate-80 even had to be closed in both directions through the Sierra on Tuesday morning, before it reopened for vehicles with tire-chain controls at 2.30pm. 

The sheriff’s office said conditions remain ‘highly dangerous’ with an avalanche warning remaining in effect through Wednesday 

Parts of Lake Tahoe could see four to eight feet of snow by the time the storm ends on Thursday

The treacherous conditions have already led several ski resorts around Lake Tahoe to fully or partially close.

The resorts have avalanche mitigation programs and were not expected to be at as high of a risk as the backcountry where travel in, near, or below the avalanche terrain was strongly discouraged, the Sierra Avalanche Center of the Tahoe National Forest said.

‘It’s particularly dangerous in the backcountry right now just because we’re at the height of the storm,’ said Brandon Schwartz, Tahoe National Forest lead avalanche forecaster at the center.

The National Weather Service has implemented a winter storm warning, which remains in effect through 10pm Thursday for the entire Sierra Nevada range.

The service warned that elevations above 3,500 feet could see four to eight feet of snow by the end of the storm. 

The Nevada County Sheriff’s Office is leading the response and is being assisted by Nevada County Search and Rescue, the Placer County Sheriff’s Office, Tahoe Nordic Search and Rescue, the Washoe County Sheriff’s Office, Washoe County Search and Rescue, and Truckee Fire. 

This is a breaking news story and will be updated.