Island Park

Dangerous avalanche conditions exist. Last week, 2-3 feet of snow loaded weak layers and dangerous persistent slab avalanches failed on many slopes. Windy conditions and 3-6” of new snow during the day will increase the likelihood of triggering large wind slab and persistent slab avalanches. Avoid traveling on and underneath slopes steeper than 30 degrees, especially those with drifts from recent wind-loading. Plans to do otherwise are risky and require extensive evaluation of slope consequences and snowpack instability.

We are deeply saddened to report that an avalanche killed a snowmobiler in the Centennial Mountains in Island Park on Sunday. Preliminary information is posted on our website, and will be updated as we gather information.

At the risk of preventing a snowstorm, we are issuing an AVALANCHE WARNING for the Cooke City area. It is beginning to snow, and we expect a foot or more by this evening. Yesterday, wind speeds increased, leading to drifting snow and a huge natural avalanche in the Sheep Creek drainage (observation). Heavy snowfall and strong winds throughout the day will rapidly load weak layers in the snowpack, creating very dangerous avalanche conditions. Human-triggered and natural avalanches failing as storm slab and persistent slab avalanches are likely. Avalanches will be largest in wind-loaded terrain, but instability will be present on all slopes, whether from fresh drifts, new snow, or persistent weak layers. Avoid travel on and underneath slopes steeper than 30 degrees. The avalanche danger is HIGH at all elevations in Cooke City.

Dangerous avalanche conditions exist in the Island Park and Lionhead areas and the Southern Madison and Southern Gallatin Ranges. Last week in the Island Park and West Yellowstone areas, 2-3 feet of snow loaded weak layers and dangerous persistent slab avalanches failed. In the Northern Gallatin and Northern Madison Ranges, less snow fell last week, and instability has been less widespread, but the recipe for persistent slab avalanches exists (Hyalite video, Portal Creek video). Today, new and wind-drifted snow will contribute to persistent slab and wind slab instability, making human-triggered avalanches likely.

Tragically, in Island Park, a snowmobiler died in an avalanche on Sunday (preliminary report), and five riders were caught in two separate slides with one full burial and four partial burials on Friday and Saturday (details av. 1, details av. 2). Yesterday, the GVSA Groomer noted two fresh wind slab avalanches on Sage Peak (observation). On Saturday, skiers triggered an avalanche above Hebgen Lake from 20 feet away (observation). In the Southern Gallatin and Southern Madison Ranges, a remotely-triggered avalanche near Bacon Rind (observation) and whumphing collapses through the weekend demonstrated instability (observation 1, 2, 3).

In the Lionhead and Island Park areas and the Madison and Gallatin Ranges, theavalanche danger is CONSIDERABLE. Avoid traveling on and underneath slopes steeper than 30 degrees, especially those with drifts from recent wind-loading. Plans to do otherwise are risky and require extensive evaluation of slope consequences and snowpack instability.

Avalanches have been unlikely in the Bridger Range(video),  but new snow and strong winds today will increase the danger and make wind slab avalanches possible. With 2-4” of new snow expected, avalanches will generally be small, but could reach one foot deep in heavily wind-loaded terrain. Fresh avalanches, shooting cracks, drifts, and snowfall amounts surpassing forecasts are indicators of instability. Consider the consequences of smaller slides in your selected terrain, and back out of steep slopes where instability and consequence overlap. The danger will rise to MODERATE on wind-loaded slopes and remains LOW in non-wind-loaded terrain in the Bridger Range.