Island Park

New snow and wind created fresh drifts of snow which could avalanche under the weight of a person, and they are adding weight to buried weak layers on some slopes. Choose slopes without fresh drifts of snow and watch for cracking, collapsing or recent avalanches as signs the snowpack is unstable. Slopes to be extra cautious of, where avalanches could break deeper on old weak snow, are those that had snow during the dry spell prior to Thanksgiving week.

Dangerous avalanche conditions exist throughout the forecast area. Wind increased yesterday and overnight, and drifted recent snow into thicker slabs. The new and wind-drifted snow is a problem on its own and may be unstable, especially on freshly wind-loaded slopes. On some slopes, slabs of new and wind-drifted snow are adding depth and weight on top of buried weak layers, making large to very large avalanches likely today.

Over the weekend we recorded over a dozen avalanches that were large enough to bury or injure a person, a few of which were much larger, plus many smaller slides (list and details here). Activity was widespread with slides reported near Big Sky (Beehive Basin), Cooke City (The Fin), Hyalite (Mt. Blackmore) and the Bridger Range (Saddle peak). Yesterday, Big Sky ski patrol triggered widespread persistent slab avalanches during avalanche mitigation work, some of which were among the biggest they have seen in certain areas.

Potential size and likelihood of avalanches are larger in areas that received the most snow over the weekend, and travel advice is simple: Avoid crossing slopes steeper than 30 degrees and the flatter terrain below steep slopes, especially where slopes are actively being loaded by wind-drifted snow.

Snowfall totals since Thursday are:

28” = 3.8” snow water equivalent (SWE) in the Bridger Range,

27” = 2.5” SWE near Cooke City,

18” = 1.7” of SWE near Big Sky and in Hyalite.

10-12” = 1.0-1.3” SWE near West Yellowstone and Island Park.

Near Bozeman, Big Sky and Cooke City, the avalanche danger is HIGH at upper elevations and CONSIDERABLE otherwise. 

Where less snow fell over the weekend, a few inches of snow and strong winds last night creates similar avalanche problems, but the likelihood and potential size of avalanches is slightly lower than elsewhere. Watch for signs of instability like recent avalanches, cracking or collapsing, and be cautious of slopes steeper than 30 degrees. Avalanche danger is CONSIDERABLE at upper elevations near West Yellowstone, Island Park, the southern Madison and southern Gallatin ranges.