The Jackson Hole News&Guide checks in with the Bridger-Teton Avalanche Center to bring readers weekly snowpack reports and summaries. Find avalanche reports, snow conditions and new features at JHAvalanche.org. Backcountry travel in avalanche terrain is inherently dangerous. This report is not meant to replace your own information gathering, only to be one source, and is not a replacement for taking an avalanche safety course.
Weather: It was a dry week around Jackson Hole. Rendezvous Bowl at Jackson Hole Mountain Resort saw just 6 inches of snow after a week of mostly sunny days.
The cold, clear conditions created widespread surface hoar, Avalanche Center Director Bob Comey said, but the feathery surface weak layer grew on mostly soft snow. As new snow falls and has some time to adjust, the danger should pass as the precipitation envelops and bonds to the surface hoar.
Snowpack: The same problems that have plagued the region for the past month and a half are still around. Buried basal weak layers from a dry period in November have created dangerous avalanche conditions that are starting to result in some big slides.
After a widespread avalanche cycle near the beginning of the last storm, around Jan. 5 and 6, things have toned down, but a few large slides over the weekend show the danger of the persistent weak layers.
Most slides around Jan. 5 and 6 were in the new snow, and while many were about 12 inches deep, several were reported to be 48 inches, reaching the basal weak layers. Four slides over the weekend — Mount Wagner, near Slate Creek, Observation Peak and Repeater Ridge — were in southern ranges and between 3 and 4 feet deep.
In the Mount Wagner slide a snowmobiler was caught after riding on the slope, but the other two were remotely triggered, meaning a snowmobiler or skier caused the slide from far away. Remotely triggered slides are evidence of the potential for propagation in the weak layer, and of instability.
“That weak layer’s trying to adjust to this,” Comey said. “It’s just making very slow progress.”
Outlook: A snow system was set to move in Tuesday night, though it could be quick. A winter weather advisory from the National Weather Service predicted the storm could drop up to 16 inches through Wednesday night before clearing out.
“This is going to add a little bit of load onto this systemic weak layer, and we’ll see if it’s enough to reactivate it,” Comey said.
Avalanche Center forecasters have been debating when the appropriate time would be to downgrade the danger at mid- and upper elevations to moderate, but if the storm comes in heavy that will likely keep the danger at considerable.
People have been “doing a good job” choosing ski routes, Comey said, though the slopes of Twin Slides and Glory Bowl were pretty heavily skied following the past storm cycle, despite the considerable danger rating. However, he worries about “message fatigue” coming from forecasters and “patience fatigue” on the part of skiers.
Waiting around for the deep snowpack that makes bigger, steeper lines safe can drag on skiers, especially as storms deposit just a foot or so at a time. Jumping on those slopes before the weak layers are buried deep enough could be a dangerous mistake, as any resulting slides will be larger and made up of harder slabs, which are more likely to cause trauma and injuries.
That these larger, persistent slabs are more dangerous is taken as gospel in the avalanche forecasting world, as noted by Utah Avalanche Center forecaster and writer Bruce Tremper in his book “Avalanche Essentials,” even though the slides are harder to trigger.
Skiing slopes with a deep persistent slab problem, he wrote, is “like playing Russian roulette with a pistol that has 99 empty chambers and 1 chamber loaded with a 44-magnum bullet.”
— Tom Hallberg