Increasing winds and another 2-4” of snow today that will fall as temperatures warm will make recent and wind-drifted snow unstable. Conditions are most dangerous at upper elevations, where greater amounts of snowfall and wind loading make human-triggered wind slab avalancheslikely. Larger slides breaking 2-3 feet deep on buried weak layers are most likely on slopes with the added weight of wind-drifted snow, although wind loading is not a prerequisite. Enjoy wind-sheltered terrain after evaluating the top three feet of the snowpack for instability from buried weak layers. Avoid slopes where active drifting, shooting cracks, or other indicators of instability are present.
While less likely than fresh wind slab avalanches, the threat of large persistent slab avalanches breaking 2-3 feet deep should be the primary driver of terrain selection.
New snow will likely hide evidence of hard wind slabs formed during last week's extreme winds.
For the last few days, the most recent snowfall (2 feet since Thursday) and avalanche activity have centered around Cooke City, where dangerous avalanche conditions exist. Human-triggered wind slab and persistent slab avalanches are likely. Some highlights from Sunday include, a group of skiers remotely triggering an avalanche that broke 3-4 feet deep (observation and photos), a natural avalanche breaking 500’ wide on the Woody Ridge mowing through small trees (details), a block of cornice on Henderson Mountain triggering a large wind slab avalanche (details and photos), and snowmobilers triggering an avalanche that broke several feet deep below Henderson Bench (details and photos). We have recorded more than a dozen large, human-triggered, and natural avalanches in our avalanche log this weekend.
New and wind-drifted snow today will keep the snowpack teetering on the edge. Enjoy the deep powder on slopes less than 30 degrees in steepness, while avoiding avalanche terrain and runout zones. Plans to break above the 30-degree mark thread a dangerous needle. The danger in Cooke City is CONSIDERABLE.
In the Madison and Gallatin Ranges, 5-8” of snow fell this weekend. Increasing winds and another 2-4” of snow today, which will fall “upside down” as temperatures warm, will make the recent and wind-drifted snow more unstable. Conditions are most dangerous at upper elevations, where more snow and wind-loading make human-triggered wind slab avalanches breaking 1-2 feet deep likely. Larger, persistent slab avalanches breaking 2-3 feet deep on buried weak layers are most likely on slopes with the added weight of wind-drifted snow, although slides a week ago in the Little Bear, Portal Creek, and Big Sky areas demonstrate that wind loading is not a prerequisite. On Saturday, Alex noted in the Beehive Basin area that buried weak layers produced one large collapse under a hard wind slab and propagated failure in tests (observation).
The avalanche danger is CONSIDERABLE in the upper elevations of the Gallatin and Madison Ranges, specifically on wind-loaded slopes. Enjoy wind-sheltered terrain after evaluating the top three feet of the snowpack for instability from buried weak layers. Avoid slopes where active drifting, shooting cracks, or other indicators of instability are present.
Less recent snow fell this weekend in the Bridger Range, Island Park, and Lionhead areas, and less is expected today. Persistent slab avalanches breaking a couple of feet deep, like the one triggered on the west side of the Bridger Range last week (video), remain possible and are the primary concern. Avalanches related to new and wind-drifted snow will generally be thin and less consequential. Plan to dig three feet deep to evaluate weak layers for instability before considering steeper terrain (Ian’s Lionhead video) or stick to slopes less than 30 degrees. The danger is MODERATE in the Bridger Range, Lionhead, and Island Park areas.
