Cooke City

Strong winds are transporting the 1-2” of new snow into unstable drifts. Use stiffening snow surfaces, shooting cracks, and visual clues to identify and avoid potential problem areas. Persistent weak layers buried 1-2 feet deep may result in avalanches in wind-sheltered terrain, but conditions are most dangerous on slopes where these problems overlap. Seek out smaller, wind-sheltered slopes and areas free of terrain traps, and if signs of instability are present, terrain less than 30 degrees steep.

Watch for signs that daytime snowfall is making conditions more dangerous. 

An avalanche that broke widely across a slope at Buck Ridge in the Northern Madison Range yesterday is the canary in our mountainous coal mine (video and details). Dangerous avalanche conditions exist in the Island Park and Lionhead areas, and the Southern Madison and Southern Gallatin Ranges, where 5-10” of new snow is getting rapidly loaded onto slopes by strong winds. Human-triggered avalanches are likely on wind-loaded slopes. Persistent weak layers buried 1-2 feet deep exacerbate the situation and may result in slides breaking widely and triggering avalanches from lower-angle terrain near steep slopes.

Farther north in the Northern Gallatin, Northern Madison, and Bridger Ranges, and across in Cooke City, less snow has fallen, but howling winds are transporting new and recent snow into unstable drifts. Yesterday, skiers north of Cooke City spotted a natural wind slab avalanche on Wolverine Peak (photo and details), and nearby, others intentionally triggered an 8-10” deep slide on a test slope (observation), and skiers in the Northern Bridger Range watched rapidly drifting snow.

Today, instability within the new and wind-drifted snow will be easy to find, and wind slab avalanches are the primary concern. Expect drifts in unusual locations as winds have come from the east and south and will shift back to the more typical southwest and west directions today. Use stiffening snow surfaces, shooting cracks, and visual clues to identify and avoid potential problem areas. Seek out wind-sheltered terrain where conditions are safer.

The second and more challenging problem is a widespread weak layer buried 1-2 feet deep throughout the forecast area (video and observation). The potential for persistent slab avalanches is increasing. There have already been some large persistent slab avalanches and plenty of whumphing collapses (avalanche activity). I don’t know when we’ll hit the tipping point toward widespread instability, but I will be selecting terrain conservatively, looking and listening for signs of danger, such as avalanches, cracking, collapsing, and unstable test results, while the snowpack gets loaded. Conservative terrain selection means: smaller slopes, areas free of terrain traps, and if signs of instability are present, terrain less than 30 degrees steep without steeper terrain above.

The danger is CONSIDERABLE in the Island Park and Lionhead areas, and the Southern Madison and Southern Gallatin Ranges, where the most snow fell, and heavy snow is expected today. Conservative terrain selection and careful snowpack assessment are essential for a safe day in the mountains.

The danger is CONSIDERABLE on wind-loaded slopes in the Northern Madison, Northern Gallatin, and Bridger Ranges and in the mountains near Cooke City, and MODERATE in wind-sheltered terrain. Identify and avoid wind-loaded slopes, and evaluate for instability related to buried weak layers before considering slopes steeper than 30 degrees.