Archived Avalanche Information (for accident reference)

Good morning. This is Dave Zinn with the Gallatin National Forest Avalanche Forecast on Monday, December 27th at 7:00 a.m. This forecast does not apply to operating ski areas.

Mountain Weather

In the last 24 hours, the mountains around Cooke City and West Yellowstone along with the Southern Madison and Southern Gallatin Ranges received 7-10" of new snow with 5-8" in the mountains around Bozeman and Big Sky. Temperatures are in the single digits to low teens F with south to southwest winds blowing 20 to 25 mph. Today, the thermometer will not change much with highs in the single digits to low teens F, winds will be 5-15 mph from the southwest to northwest and by morning, the mountains around Cooke City and West Yellowstone will have another 2-4" with a trace to 1" everywhere else.

Snowpack and Avalanche Discussion
Southern Madison Southern Gallatin Lionhead Range Cooke City

Consistent snowfall for the last five days brings our storm total to 31-37" equal to 2.6" of snow water equivalent (SWE) in the Southern Madison and Southern Gallatin Ranges and 3.5" of SWE in the mountains around West Yellowstone and Cooke City. The combination of recent snow and moderate winds from the southwest creates dangerous avalanche conditions. While the wind will ease off today, recently formed 1-4' deep drifts will remain unstable. Avalanches failing on weaker layers of snow in the mid and lower snowpack are a possibility and would be large and dangerous. This reality kept Doug and me out of avalanche terrain yesterday at Lionhead (video). Alex's advice from the Taylor Fork and mine from last week in Cooke City holds true today, steer clear of wind-loaded slopes and carefully assess the snowpack and terrain features in non-wind-loaded areas prior to entering any avalanche terrain.

With the significant caveat that visibility is limited, we have not seen or received reports of widespread avalanche activity during this storm. We do have good indicators of instability such as large "whumphs" triggered by skiers near Bacon Rind on Friday (details) and unstable snowpack tests throughout the area failing and propagating within new snow layers and on weak layers near the ground. If you see an avalanche in the mountains today, snap a photo and submit it through our observations form.

The avalanche danger is rated CONSIDERABLE on wind-loaded slopes where human-triggered avalanches are likely and MODERATE on non-wind-loaded slopes where avalanches are possible.

Cooke City Bottom Line: Consistent snowfall for the last five days in the mountains around Cooke City, West Yellowstone and in the Southern Madison and Southern Gallatin Ranges creates dangerous avalanche conditions. Human-triggered avalanches are likely on steep wind-loaded slopes and large avalanches could break deeply on buried weak layers. Avoid recently wind-loaded terrain and carefully assess the snowpack and terrain prior to approaching steep non-wind-loaded slopes.