Island Park

Avalanches are unlikely today, but THIS WILL CHANGE TONIGHT. If snowfall starts earlier than expected today, and when winds increase, lookout for shallow fresh drifts. The storm tonight is forecast to favor the mountains near Island Park and West Yellowstone and avalanche danger will significantly increase tomorrow.

Today there are two main avalanche problems to watch for. The first and potentially larger are persistent slab avalanches breaking 8-16” deep. These are possible where last week’s snow deposited thick slabs on top of sugary weak layers that formed in January. The second problem is freshly formed drifts which can break under the weight of a person. These wind slab avalanches will be shallower, but easier to trigger than the previously mentioned persistent slabs. Steep slopes where these problems overlap will be the most dangerous.

Near Bozeman and Big Sky southwest winds are drifting 3-4” of new snow into fresh wind slabs which are easy to trigger. Yesterday in Hyalite, winds increased and formed thin drifts, and skiers triggered small wind slabs prior to last night’s new snow (observation). Wind slabs today could be larger with the addition of the drifted new snow. Where no new snow fell over the weekend today’s stronger winds could form fresh drifts of any soft snow left over from last week or snow that falls this afternoon. Avoid steep slopes with fresh drifts, especially where a slide could push you into trees, a gully, or over a cliff. 

Additionally, fresh drifts will add weight to weak layers buried below last week’s snow, and increase the chances to trigger a larger persistent slab avalanche. These types of slides are also possible on slopes that are not recently wind-loaded, but slightly less likely there. This problem is tricky to assess because there is a lot of variability in the snowpack structure which creates high variability in snow stability. You can dig down to look for and assess buried weak layers, but be cautious of any seemingly stable findings. There is a chance you’ll get collapsing of the snowpack or unstable test scores, but maybe not. An observation from Emigrant Peak yesterday is a good example of the variability that makes this persistent slab avalanche problem tricky to assess. The safest bet is to choose smaller slopes where avalanches can’t break as wide and run long, and slopes that do not have terrain traps like trees, cliffs or confined gullies.

The avalanche danger is MODERATE in the Bridger, Madison and Gallatin Ranges, and near West Yellowstone and Cooke City.

Near Island Park there was less snow last week, avalanches are unlikely, and the avalanche danger is LOW today. THIS WILL CHANGE TONIGHT. If snowfall starts earlier than expected today, lookout for shallow fresh drifts. The storm tonight is forecast to favor the mountains near Island Park and West Yellowstone and avalanche danger will significantly increase tomorrow.