Lake Tahoe avalanche explained by warm weather

How warm weather helped cause the Lake Tahoe avalanche

By Tom Metcalfe edited by Andrea Thompson

Most of the western United States, including the Lake Tahoe region of California and Nevada, experienced an unusually warm winter, breaking records in many areas. And that unusual heat may have caused a disastrous avalanche at the region’s Castle Peak mountain that buried a group of skiers on Tuesday.

Weeks of warm weather may have caused the thin layer of snow at high elevations in the Lake Tahoe area to partially melt, creating an unstable base layer that was then covered by a layer of snow over the past few days, says climatologist Daniel Swain of the California Water Resources Institute. According to the National Weather Service, parts of the region received three feet of snow in 24 hours, and more than five feet of snow are estimated to have fallen there since Sunday.

“There was a very sudden shift from warm, dry snowfall to very heavy snowfall,” Swain said. “It was probably in the area where this avalanche occurred.”

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This combination of an unstable base beneath a thick layer of fresh, unconsolidated snow is one of the most dangerous causes of mountain snow avalanches, Swain says. And it appears that led to Tuesday’s avalanche that trapped skiers at Castle Peak, near the town of Truckee, Calif., and a few miles northwest of Lake Tahoe.

The bodies of eight skiers have been found, and a ninth person is missing but presumed dead, according to media reports. Six other skiers in the group survived but had to be rescued by a vehicle called a snowcat due to the blizzard-like conditions.

David Reichel, executive director of the Sierra Avalanche Center, which issues forecasts for the Tahoe-Truckee region, says his group is monitoring the recent weakening of the snow surface. “We have made several videos discussing these problematic layers over the past week,” he adds.

Many scientists expect that rising temperatures due to climate change will increase dangerous avalanches, Swain says. While warming may suggest less snowfall, that’s not all. Lower elevations are expected to see less snow, but higher elevations could actually see heavier snowfall as temperatures there remain below freezing but warm enough that there will be more moisture for storms.

“The influence of climate change on avalanches is currently being studied, but…the likelihood of these dry, warm conditions preceding very heavy snowfall has increased in California,” says Swain.

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