The October snowfall seemed like a blessing to those looking forward to ski season, but it caused a few backcountry skiing veterans to grumble. If it didn’t keep snowing to cover that first layer of snow, or if that layer didn’t melt completely, the snow would rot in place and form a weak layer that could last for weeks or longer.
Utah Avalanche Center Forecaster Nikki Champion said that’s exactly what happened.
“So right now we've got a pretty similar setup to last year,” Champion said. “We got that early season snow in October and then that kind of sat over November and December. Those grains became weak and sugary and that's what's sitting on the base of our snowpack to the north- and west- and east-facing aspects.”
Champion said the sunbaked southern flanks of mountains generally had the snow from the October storms melt completely, meaning they are safe from what’s known as the “persistent weak layer” that’s found elsewhere.
But she cautioned those areas would have less coverage, so riders should watch out for stumps and rocks that might be just slightly buried.
“So there is good news. So that persistent weak layer, it’s just sitting on those northwest- through east-facing aspects,” Champion said. “That means that those southerly facing aspects don’t have that weak, faceted snow.”
The Utah Avalanche Center received reports of 40 avalanches from Friday, Dec. 10, to Thursday, Dec. 16. That included one in an area called Katie’s, which is in The Monitors region of the Park City Ridgeline.
The Avalanche Center’s report includes a photo with a person standing next to the crown, holding a ski pole at shoulder height to show how deep the slide was. The report says it was 1,100 feet wide.
Forecaster Greg Gagne said conditions are dangerous on mid- and upper-elevation slopes.
“What really concerns me going forward is that I think the snowpack is going to be a little less reactive, fewer collapses, maybe fewer remotely triggered avalanches, but it does nothing more than give us a false sense of a stable snowpack,” Gagne said. “So please don't be lulled into this sort of thinking. Conditions are dangerous on these aspects where that persistent weak layer is present.”
There are two things that can make the weak layer go away, Champion said: snow and time. She said persistent, smaller storms could help heal the snowpack, as could a massive amount of snow that would bury the layer far enough that forces from a skier or rider wouldn’t reach down to it. That could take two meters of snow or more.
Gagne urged people to use caution as they head out into the mountains.
“With sunshine forecasted for the weekend people have to, can't let their guard down,” he said. “And this problem is going to persist certainly through the weekend and into next week, so be safe out there.”
The forecasters said there are plenty of ways to have fun in the backcountry on slopes less steep than 30 degrees and on southerly facing aspects.
