Island Park

Wind slab avalanches of recently drifted snow are likely. Additionally, large to very large persistent slab avalanches can break on weak snow near the bottom of the snowpack. Avoid slopes steeper than 30 degrees, and be extra cautious crossing below steep slopes.

Today there are two main avalanche problems which vary in likelihood and size across the forecast area. Wind slab avalanches of recently drifted snow are likely at upper elevations in all mountain ranges, and may be deeper or break in older drifts where more snow fell over the last week, like near Cooke City and the southern parts of our forecast area. 

Additionally, large to very large persistent slab avalanches can break on weak snow near the bottom of the snowpack. These can be 2-6 feet deep in areas with shallower snow depths (avalanche on Buck Ridge), and up to 8-15 feet in deeper areas (Avalanche on Scotch Bonnet earlier in the week).

Over the past ten days the mountains near Cooke City, West Yellowstone, Island Park, and the Southern Madison and Southern Gallatin Ranges have received steadier, heavier snowfall compared to elsewhere. This makes the persistent slab problem potentially larger and more likely. Recent large avalanches in the Taylor Fork were triggered by snowmobilers, remotely from flat terrain (Taylor Fork observation). These are good examples of what is possible, and displays the need to avoid slopes steeper than 30 degrees, and be extra cautious crossing below steep slopes, in these areas.

In the Northern Madison and Northern Gallatin ranges there has been less snowfall over the last ten days, but weak snow near the bottom of the snowpack exists and makes large persistent slabs possible, as shown by a recent slide in Lone Lake Cirque. If you intend to cross steep slopes, carefully assess the snowpack for wind-loading and buried weak layers, and evaluate terrain for consequences of a slide. 

In the Bridger Range the persistent slab problem is less widespread largely due to most of the early season snow melting instead of becoming weak. Before entering avalanche terrain, dig to look for the weak snow near the ground, and assess the stability of the recent snow and wind-drifts. Adjust your plans if you find signs of instability (Bridger Range observation).

Near Cooke City, West Yellowstone and Island Park, avalanche danger is CONSIDERABLE and avalanche terrain should be avoided. Near Bozeman and Big Sky, danger is CONSIDERABLE at upper elevations and MODERATE otherwise. Steer clear of wind-loaded slopes and carefully assess the snowpack for buried weak layers if you plan to cross steep slopes.