Cooke City

Persistent weak layers buried 2-3 feet deep, drifting snow, and above-freezing temperatures contribute to instability today. Recreating in terrain less than 30 degrees steep is a sure way to avoid avalanches. If steeper terrain is in your travel plan, seek out wind-sheltered slopes, evaluate the upper three feet of the snowpack for dry and wet snow instability, and choose simpler pitches free of terrain traps to reduce the potential consequences of a slide.

The last four days were active, with twenty-one avalanches recorded in our log. Throughout the forecast area, there are three types of avalanches that you could encounter in steep terrain.

1. Persistent Slab Avalanches breaking 2-3 feet deep and propagating widely on buried weak layers. Backcountry skiers and riders may trigger avalanches from a distance that slide on nearby steep slopes, so be cautious while traveling below steep terrain and limit overhead exposure when possible. Watch the video of riders in the Northern Gallatin Range on Saturday to see a remotely triggered slide. Assume weak layers are present or get out your shovel and look for yourself because you are unlikely to observe clear signs of instability before triggering an avalanche.
2. Wind Slab Avalanches failing 1-3 feet deep on slopes loaded with drifting snow from the windy period that began Saturday and continues today. These will be thickest in the mountains around Bozeman and Big Sky, where the most snow fell last week. Wind loading will not follow normal distribution patterns and may be found at many elevations due to the strong and extreme winds. Shooting cracks, textured and stiffening snow surfaces, and obvious drifts are indicators of potential instability. Saturday’s snowboarder-triggered avalanche near a ridgeline in the Northern Madison Range is a good example (details).
3. Wet loose avalanches that start at a narrow point and spread. Increasing clouds and windy conditions should limit instability, but don’t discount it as southern aspects and rocky terrain heat up. These are most dangerous in confined areas like gullies. Rollerballs and pinwheels, and wet snow more than a couple of inches deep are early indications that snow is destabilizing.

Conditions remain complicated with multiple avalanche problems that overlap on some slopes and could occur in isolation on others. However, the likelihood of triggering an avalanche has decreased as we move further away from last week’s snowstorm, and the rates of change (wind-loading and warming) have decreased (weather log). The danger is MODERATE throughout the forecast region.

What should you do:

1. The easy answer is to avoid avalanches by playing in terrain less than 30 degrees steep.
2. If slopes steeper than 30 degrees are part of your plan, seek out slopes sheltered from the wind, avoiding steep wind-loaded slopes.
3. Watch for shooting cracks and wet snow, and evaluate the upper 3 feet of the snowpack with an extended column test. Visible weak layers and propagation in your test are both reasons to return to lower-angle slopes (less than 30 degrees).
4. Choose smaller, lower-angle terrain with fewer terrain traps, such as trees, rocks, and gullies, to minimize the potential consequences of an avalanche.