Winter conditions in Utah this year are ripe for avalanches. And big ones.
Avalanche danger ranges from considerable to high right now across the state, according to the Utah Avalanche Center, with the potential for slides “up to five feet deep, several-hundred feet wide and likely unsurvivable.”
The danger was high over the weekend, too, when eight skiers were caught in an avalanche on the Wilson Glade slope of Millcreek Canyon. Six people were buried and four died — all in their 20s from the Salt Lake City area, experienced skiers and equipped with avalanche gear.
The tragedy brought Utah’s avalanche death toll to six, after two people died earlier this month near Park City ridgeline. Saturday’s event was the worst avalanche accident since four people died in the La Sal Mountain Range east of Moab in 1992, the Avalanche Center said.
The dangerous conditions this winter stem from persistent weak layers of snow, said Mark Staples, director of the center. Long periods of dry weather through November and December weakened the snow pack. So when several storms came through over the last few weeks, the snow layers below started to crumble.
A range of other weather factors, such as warm temperatures and wind conditions, have also made the top layers of snow thicker and more cohesive, causing it to break over wider areas. The deadly avalanche on Saturday was three and a half feet deep and about 1,000 feet wide, according to a report from the center.
“A month ago, some of the avalanches weren't even big enough or deep enough to bury somebody,” Staples said. “Through time, we've seen them grow in size and become more destructive and more deadly.”
Judging a mountain for avalanche potential is difficult, even for the most seasoned backcountry skiers, he said. For other adventure sports, like mountain biking, people can easily point out which areas might present danger.
“You don't see that with snow, when you have weak foundation layers lurking beneath,” he said. “What you see is a beautiful ski run.”
He said backcountry skiers can also run into trouble by using their past experience as a guide. They might make it safely down the mountain but never know how close they came to getting caught. That can create a false sense of security, he said.
It’s not unusual to have weak layers of snow, said University of Utah atmospheric sciences Professor Jim Steenburgh. What is unusual is how persistent they are this year. Normally, more snowfall would eventually develop a deeper, stronger snowpack, but Steenburgh said that hasn’t happened yet.
He said he would not attribute conditions this year to climate change. There are certain trends that have been shaping up over time, such as less snow falling at lower elevation. But avalanche conditions are dependent on the weather in any given year and can vary from year to year, so ascribing current conditions to a long term trend is difficult.
Still, he said the climate — and winters — are changing.
“The dice are becoming increasingly loaded for warmer winters and, in the lower elevations, a less persistent snowpack and a greater fraction of precipitation falling as rain instead of snow,” Steenburgh said.
Even under uncertain conditions, Staples said it is possible to safely ski the backcountry right now. But people should avoid avalanche terrain, that is, any slope steeper than 30 degrees and the areas below where avalanches could slide into.