Extended Dry Spell Created Deadly Avalanche Conditions in California Mountains

A prolonged period without snowfall in California's Sierra Nevada mountains created dangerous conditions that contributed to Tuesday's fatal avalanche near Lake Tahoe. Eight backcountry skiers died when fresh snow failed to properly bond with an existing hardened layer, creating an unstable surface that gave way during their guided tour.

An extended period without snowfall in California’s Sierra Nevada mountains created the dangerous conditions that led to Tuesday’s fatal avalanche near Lake Tahoe, according to avalanche experts analyzing the tragedy.

Craig Clements, a meteorology professor at San Jose State University who studies avalanches, explained that several feet of fresh snow landed on top of a hardened layer from earlier in the season. The two layers failed to properly connect, creating hazardous and easily triggered conditions.

“The new snow did not have time to bond to the earlier layer before the avalanche,” Clements said. The disaster claimed the lives of at least eight backcountry skiers, while six others survived the ordeal. Search teams continued looking for one missing person on Wednesday.

The skiing party had embarked on a three-day wilderness expedition in the Sierra Nevada mountains when the avalanche struck Tuesday morning, coinciding with a powerful winter storm battering the West Coast.

According to Clements, avalanche risks typically peak during the initial 24 to 48 hours following significant snowfall, and officials had already posted avalanche advisories for the region.

The meteorology expert described how prolonged dry conditions, which had persisted in the Sierra Nevada since January, cause snow crystals to transform and develop angular or rounded shapes over time.

When substantial amounts of new snow accumulate on these altered crystals, the different layers frequently cannot form proper connections. This creates what avalanche specialists call a storm slab positioned above a weaker foundation layer.

“Because it’s on a mountain, it will slide,” Clements explained, noting that any shift in pressure from above or below can trigger the slide. While some avalanches occur naturally, human activity in the area can also set them off. Officials have not yet determined what caused Tuesday’s avalanche to begin.

Clements noted that more regular snowfall throughout the winter season would have allowed different snow layers to bond more effectively. However, even when dangerous storm slabs develop, the hazardous conditions typically last only a few days before the new snow becomes more stable.

While climate change can create weather extremes including both drought conditions and intense precipitation events, scientists say it remains challenging to determine how this might influence avalanche patterns or locations.

Clements characterized this week’s avalanche as typical for California’s Sierra Nevada region and does not believe it connects to climate change impacts.

He described avalanches as dependent on snowfall amounts and the stability of underlying layers, calling this incident “a meteorological phenomenon, not a climate phenomenon.”

Weather reports indicate that between 3 and 6 feet of snow accumulated since Sunday, when the group began their expedition. The region also experienced below-freezing temperatures and powerful winds. The Sierra Avalanche Center warned Wednesday that additional avalanche threats remained, leaving snow conditions unstable and unpredictable.

Recovery teams located eight bodies near California’s Lake Tahoe following Tuesday’s avalanche, which authorities describe as the nation’s most deadly in nearly 50 years. Six members of the guided tour were rescued six hours after the slide occurred.

Nevada County Sheriff Shannan Moon announced Wednesday that investigators will examine the decision to continue with the planned trip despite storm forecasts.

The skiers had traveled Sunday to isolated mountain huts located at 7,600 feet elevation in Tahoe National Forest, bringing their own food and equipment. At 6:49 that morning, the Sierra Avalanche Center had issued an avalanche watch for the area, warning that large slides were probable within the following 24 to 48 hours.