Cooke City

Watch for signs of unstable wind slabs such as cracking across the snow surface, and be cautious of slopes with signs of recent wind loading, like a textured or pillow-like surface and slopes below cornices. Steer clear of suspect slopes where a slide could push you into a terrain trap like cliffs, trees or gullies. It won’t hurt to dig down and look for weak layers before committing to steep slopes.

Wind Slab Avalanches

Throughout the forecast area strong winds drifted recent snow into thicker slabs that can avalanche under the weight of a person.

Near Cooke City, Island Park, Lionhead, and the Southern Madison and Southern Gallatin Ranges 3-4+ feet of snow fell over the last week and large avalanches could break where wind has drifted that snow into stiffer slabs.

The Bridger, Northern Madison, and Northern Gallatin Ranges received less snow, 8-12” over the last week, but winds were steady and strong since Friday. The last two days, skiers in the Bridger Range triggered multiple avalanches of freshly drifted snow. These were 8-12” deep and 10-25 ft wide (observation 1, observation 2) which is big enough to easily carry a person down a slope, and could potentially bury someone if the debris piles deep against trees or in a gully.

On some slopes, wind slabs were deposited on top of small, weak facets (observation from Hyalite). This weak layer does not seem to be a widespread problem, but there might be an isolated slope or two where it makes wind slabs reactive for another day or two.

Watch for signs of unstable wind slabs such as cracking across the snow surface, and be cautious of slopes with signs of recent wind loading, like a textured or pillow-like surface and slopes below cornices. Steer clear of suspect slopes where a slide could push you into a terrain trap like cliffs, trees or gullies.

Persistent Slab Avalanches

Near West Yellowstone and in the Southern Madison and Southern Gallatin Ranges an additional, more dangerous problem exists. Weak layers at the bottom of the snowpack make it possible to trigger a big persistent slab avalanche that could break many feet deep. There were widespread persistent slab avalanches in these areas the last time the snowpack was loaded (observation). Choose terrain less than 30 degrees steep, or find smaller slopes without terrain traps like trees, cliffs or gullies in order to reduce the size and consequences of a potential persistent slab avalanche. Remain cautious crossing underneath big, steep slopes as these slides can be triggered from flatter terrain that is connected to steep slopes (video).

Near Cooke City, Island Park, Big Sky, and Bozeman persistent slab avalanches are unlikely. It has been 2-4 weeks since the last persistent slab avalanche while the snowpack has been tested with the weight of new snow. If you ski or ride steep slopes, it is worth digging down to assess the snowpack for weak layers, especially where the snowpack is shallower and you could more easily affect this weak layer, like near Bozeman and Big Sky.

The avalanche danger is MODERATE throughout the forecast area.