Avalanche risks remain high in California after deaths of skiers | California

Avalanche risk remains high in Northern California’s Sierra Nevada mountains this week after the region’s deadliest snowslide in modern times.

According to experts, who have long warned that extremes will increase as the world warms, the climate crisis has paved the way for more dangerous conditions with sharper transitions between dry periods and severe storms.

High temperatures have resulted in record-low snowpack across the region, and the snow drought that has caused concern across the western United States this winter has left hillsides devoid of thick frozen layers for fresh snow to cling to. Powerful storms hit the Sierra this week, covering previously barren peaks. UC Berkeley’s Central Sierra Snow Lab measured more than 92 inches of snowfall over the past seven days.

While the return of winter weather is welcome news for water managers anxiously watching the low totals, it has led avalanche forecasters to issue stronger warnings.

“New snowfall and strong winds will occur today and continue to load our existing snowpack. Large to very large avalanches remain a serious concern,” the Sierra Avalanche Center, a nonprofit partner of the U.S. Forest Service, said in a forecast released Thursday.

Due to the warm weather in January and February, the snow density in these mountains is also much lower than normal; This means rocks, fallen trees, and other hazards are closer to the surface where they can more easily hide. Avalanche warnings were set at level four out of five; This is a designation that indicates that the potential for major avalanches is high in many areas where both natural and human-induced slides are likely to be high.

More than 8,500 daily high temperature records have been broken or tied in the western United States since December 1, according to National Oceanic and Atmospheric Administration (Noaa) data.

Much of the precipitation that would normally fall as snow and stay in the mountains for months instead falls as rain, and the rain flows faster, said Daniel Swain, a climate scientist at the University of California Water Resources Institute, in a discussion of the conditions shared online.

Before this storm surge, snow was so scarce that brown patches could be seen even at higher elevations. What followed was “extreme accumulation,” Swain said. Calling it “Sierra Cement,” the term for the heavy, dense, wet snow common in the region, he described how badlands were covered by up to 4 feet in a 24- to 36-hour period.

The sudden fall of this thick powder falls on top of the icy layer that forms during the dry months, creating a “boundary between snow layers,” Swain said. “This fits the pattern of large avalanche events we’ve seen in this part of California in the past.”

These factors created severe avalanche risks on Tuesday, when a group of 15 backcountry skiers began their trip. Although authorities have not yet determined the exact cause of the avalanche, forecasters warned that slides could easily be triggered.

The new snow did not have time to bond with the previous layer before the avalanche hit, according to Craig Clements, a professor of meteorology at San Jose State University.

When the weather is dry and clear, as it has been in the Sierra Nevada since January, snow crystals change and can become angular or rounded over time, Clements said. New heavy snow is different and does not bond to the snowpack, but forms what is known as a “storm sheet” on top of the weaker snow layer.

“Because it’s on a mountain, it will slide when triggered by any change in tension above or below, sometimes naturally, sometimes due to people passing through the area,” Clements said.

Tuesday’s avalanche has killed eight alpine skiers so far, making it one of the deadliest events in U.S. history. While there is still no news from one skier, six skiers who had been stranded for a while were rescued. The avalanche is now ranked as the deadliest such event in the United States in the past 45 years.

“The human toll is immeasurable,” forecasters at the center wrote of the tragedy, calling it “a huge blow to our society.”

Associated Press contributed reporting