JACKSON, Wyo. — This year’s unstable snowpack is not typical for the Tetons and it’s unlike any previous winters on record.
Frank Carus, Director of Bridger-Teton Avalanche Center (BTAC), and Mike Rheam, Lead Forecaster for the BTAC, explained to Buckrail why this entire season is set up to be extremely hazardous for backcountry riders. Rheam shared that comparisons could maybe be made to the 1997/1998 and 2008/2009 winter seasons, but none are really similar to this year.
“What’s unique this year is the dry December period rotted the snow at all elevations,” Rheam told Buckrail via email. “Even low elevations where there was barely enough snow to cover the slopes. This current cycle has the chance for avalanches that can propagate long distances on all aspects and elevations. The nature of the weakness is allowing for slides to be triggered remotely and avalanches are occurring on slopes that are not very steep.”
Typically, the Tetons are known for being more stable because a large amount of snow falls steadily throughout the season.
“One of the things people love about the Tetons is that it’s really good sking, really good terrain and with a remarkably stable snowpack,” Carus said. “We don’t typically have drought conditions which lead to a weak layer setup that we have now. People need to look at this snowpack as a totally different animal than they’re used to.”
“Basically, this weak layer is going to plague us, probably for the rest of the season.”
Frank Carus
BTAC received a report of an avalanche on Thursday, Jan. 18 in Grand Teton National Park (GTNP), with a crown approximately a quarter-mile in length, that started lookers far left of Ullr’s (an area between 25 Short and Mavericks) extending to the east face of 25 Short. The debris ran down 7,300 feet from the summit.
This slideshow shares four of the many regional avalanches that BTAC reported in January.
On Jan. 17, BTAC reported an avalanche on Wolf Trap, which is located beneath Avy Bowl, South of the Teton Pass. Photo Courtesy of the Bridger-Teton Avalanche Center 
Moose Brush, a 36 to 37 degree slope near Mail Cabin, avalanched earlier this season, and BTAC reported on Jan. 16 that the exact spot refilled and avalanched again. Photo Courtesy of Bridger-Teton Avalanche Center 
A large avalanche was observed on Mt. Hunt, in Grand Teton National Park, on Jan. 14. Photo Courtesy of the Bridger-Teton Avalanche Center 
On Jan. 15, BTAC reported that the north side of Static and Buck Mountain in Grand Teton National Park slid. Photo Courtesy of the Bridger-Teton Avalanche Center
According to BTAC, a bottom unstable layer formed over a long period of early season drought that lasted 23 days in December. The drought was also accompanied with cold temperatures and clear skies. These conditions created a bottom weak layer that most likely isn’t going anywhere.
Carus explained how geometric deformity in snow crystals, called near surface facets and surface hoar, has formed this bottom weak layer, which has been capped by light, low density snow.
“If you want to get really nerdy,” Carus said, “near surface facets are caused by a vapor deferential in the snow that drives warm, moist air from the base of the snowpack out into space, and that vapor will create angular edges on the snow crystals that don’t stick well to the adjacent snow grains.”
Adversely, early season snow fall that comes over a period of time will melt down snow flakes into little round particles that stick to each other, forming a stable base.
Carus explained that surface hoar is essentially frozen dew, similar to the dew seen out in fields on an early summer morning. Clear skies create radiant heat that leads to rapid cooling that draws moisture to the surface of the snowpack, and three dimensional snow feathers are formed. Surface facets and snow hoar isn’t a big problem if melting or wind comes before a snow fall to dissipate or dissolve the crystal “feathers,” but December’s clear and cold skies came with little to no wind and buried the frost feathers and near surface facets. In early January, a storm or snow load then came and preserved this facet and hoar layer.
Rheam further elaborated that the underlying sugary/faceted snow can not support the recent loading of storm events, and that this surface hoar lies on many slopes throughout all elevations.
“If you dig a pit you can see all the frost feathers and facets in a lot of places throughout the Greys and Salt River range,” Carus said. “Sadly, this base layer ends up being structurally strong, similar to champagne glasses being stacked up with a piece of plywood on top that you could maybe stand on, but a lateral motion would cause those champagne glasses to fall down. It’s the same with the surface hoar.”
The fundamental movement of skiing and snowboarding is a lateral motion against the surface of the snow.
“You basically don’t want to go into or under slopes steeper than 30 degrees and even then it’s risky because you can be standing on a lower angle spot and have a crack propagate a steeper slope that is right next to you,” Carus said. “Someone can also trigger something down on you from above.”
Carus continued to explain that while five to six feet of snow does make it harder for the weight of a skier to impact this weak bottom layer, thin spots where the wind has scoured the snow and warming temperatures, which can send moisture eight to 10 feet down, have the potential to cause massive avalanches.
“It’s a dangerous time,” Carus warned. “Even if you are an expert with managing risk and exposure in avalanche terrain, you can still make a mistake because your margins are shrinking during conditions like this.”
