California Avalanche at Castle Peak: Snow Drought Creates Dangerous Conditions, Resulting in Fatal Incident

In Northern California’s Sierra Nevada, a prolonged period without significant snowfall created conditions ripe for disaster, leading to a tragic avalanche on Tuesday. Experts explain that the incident, which claimed the lives of at least eight backcountry skiers, occurred after several feet of fresh snow landed atop a hardened base layer, rendering it unstable and prone to triggering.

Craig Clements, a meteorology professor at San Jose State University with expertise in avalanche research, noted that the new snowfall had not had sufficient time to adhere to the pre-existing icy layer. This instability was a key factor in the deadly avalanche near Lake Tahoe. While six skiers were able to survive, rescuers continued their search for one individual who remained unaccounted for on Wednesday.

The group, engaged in a three-day backcountry skiing expedition, found themselves caught in the avalanche amid a fierce winter storm battering the West Coast on Tuesday morning.

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Clements further highlighted that the risk of avalanches is particularly high within the first day or two following substantial snowfall. In light of this, authorities had already issued avalanche warnings in the area.

Here’s what to know.

What made conditions so dangerous?

When weather is dry and clear, as it had been in the Sierra Nevada since January, snow crystals change and can become angular or round over time, Clements said.

If heavy new snow falls on the crystals, the layers often can’t bond and the new snow forms what is called a storm slab over a weaker layer.

“Because it’s on a mountain, it will slide,” when it’s triggered by any change in the tension above or below, sometimes naturally but also because of people traversing the area, Clements said.

Authorities have not said what triggered Tuesday’s avalanche.

If there had been more consistent snowfall throughout the winter, different layers could have bonded more easily, Clements said. But even when a snow slab forms, the danger often only lasts a couple of days until the new snow stabilizes, he said.

Was climate change a factor?

Climate change can lead to weather extremes that include both drought and heavier precipitation, and scientists are studying how it might affect avalanches and where they occur.

Warmer-than-usual temperatures contributed to a snow drought throughout the West. But Clements said this week’s avalanche is fairly typical for California’s Sierra Nevada and he doesn’t believe it can be linked to climate change.

Avalanches are a mechanism of how much snow falls on weak or stable layers, and this one was “a meteorological phenomenon, not a climate phenomenon,” he said.

About 3 feet to 6 feet of snow has fallen since Sunday, when the group started its trip. The area was also hit by subfreezing temperatures and gale force winds. The Sierra Avalanche Center said the threat of more avalanches remained Wednesday and left the snowpack unstable and unpredictable.

What’s happening now?

Crews found the bodies of eight backcountry skiers near California’s Lake Tahoe and were searching for one more following Tuesday’s avalanche, which authorities say was the nation’s deadliest in nearly half a century.

Six from the guided tour were rescued six hours after the avalanche.

Nevada County Sheriff Shannan Moon said Wednesday that investigators would look into the decision to proceed with the trip despite the storm forecast.

The skiers traveled Sunday to remote huts at 7,600 feet (3,415 meters) in Tahoe National Forest, carrying their own food and supplies. At 6:49 that morning, the Sierra Avalanche Center issued an avalanche watch for the area, indicating that large slides were likely in the next 24 to 48 hours.