GNFAC Avalanche Forecast for Tue Mar 21, 2023

Human-triggered avalanches are likely in the mountains around Cooke City and West Yellowstone where 4-7” of new snow fell, and moderate winds are drifting snow at Lionhead Ridge.

The primary concern is large avalanches breaking on persistent weak layers deep within the snowpack. Like a recent snowmobiler-triggered avalanche north of Cooke City, these could break 2-6+ feet deep and fail widely across slopes (details and photos). In the last month, we have been lucky that a large avalanche has not injured or killed a skier or rider in the many close calls and large avalanche cycles (Avalanche Incidents, Lionhead avalanche cycle). We have used up our nine lives, and getting caught and carried in an avalanche of this magnitude could easily be unsurvivable. Choose smaller, lower-angle runs sheltered from the wind. Avoid steep wind-loaded slopes and complex terrain with traps like rocks, cliffs, and gullies. Be cautious about crossing underneath steep slopes. If there are any questions, avoid all terrain steeper than 30 degrees.

Our secondary concern is smaller avalanches breaking within the new and wind-drifted snow. While smaller, these can be big enough to bury or injure a skier or rider on slopes where terrain features worsen the consequences of getting caught.

The danger is CONSIDERABLE.

The mountains around Bozeman and Big Sky received 2-4” of new snow. The primary concern is large avalanches breaking deep within the snowpack on persistent weak layers. Alex and I rode in the Taylor Fork area on Sunday, where we saw several deep slab avalanches that failed last week (video, observation and photos). Deep slab avalanches have also occurred in the northern ranges of the advisory area, albeit with lesser frequency (Hyalite Peak slide, Northern Bridgers slide). Manage this problem with conservative terrain choices. Pick smaller slopes with less exposure to the wind and without complicating factors like cliffs and rocks or stay in terrain less than 30 degrees.

Yesterday in Frazier Basin, we found a weak snowpack structure in one of our pits and observed five loose snow avalanches on a steep face. These slides were only an inch or two deep, but they ran a long way and highlighted that the new snow might bond poorly to a melt-freeze crust that formed on many slopes (video, observations). Watch for signs of instability like shooting cracks and recent avalanche activity within the new snow if you plan to enter avalanche terrain.

Heightened avalanche conditions exist, and danger is MODERATE.

Please share avalanche, snowpack or weather observations via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).

Human-triggered avalanches are likely in the mountains of Island Park, where 5-7” of new snow fell, and moderate winds are drifting snow. Avalanches within the new and wind-drifted snow will be large enough to carry and bury a rider or skier. Larger slides are possible on heavily wind-loaded slopes or where there are underlying weak layers. Choose smaller, lower-angle slopes that are sheltered from the wind and avoid steep wind-loaded terrain and complex slopes.

See Doug’s video for a rundown on the aftermath of last week’s avalanche warning. Snow bikers in the bowl of Mount Jefferson saw further evidence of a large avalanche cycle noting a 6’+ deep crown on a heavily wind-loaded slope (photo).