BOZEMAN - The Gallatin National Forest Avalanche Center reported Tuesday morning that recent snow has the same structure and loading patterns as a deadly avalanche that claimed the lives of two snowmobilers on Monday.
According to officials, the mountains around Cooke City and West Yellowstone and the Southern Madison and Southern Gallatin Ranges picked up 2-3” of new snow bringing the storm totals to 33-40” of new snow in the last week (2.8-3.7” of snow water equivalent - SWE).
On Monday, December 27th, two snowmobilers died in an avalanche yesterday on Scotch Bonnet Mountain north of Cooke City (details and photos). Another group of skiers near Henderson Bench reported a natural avalanche likely triggered by a cornice fall that broke 5-6’ deep on buried weak layers near the ground (details and photo).
Members of Park County Sheriff Search and Rescue arrived to assist with rescue and recovery efforts.
The same fundamental structure and loading patterns resulting in avalanches near Cooke City exist in the Lionhead area (video), the Southern Madison (video) and the Southern Gallatin Ranges. Human-triggered avalanches are likely where winds from the last week drifted the 3’ of new snow onto steep slopes. Avalanches may break within the layers of new snow and wind-drifted snow or 5-6’ deep on weak layers buried in the lower third of the snowpack. Keep it simple and avoid steep wind-loaded slopes. Avalanches are possible on non-wind-loaded slopes where you should utilize thorough snowpack assessments, consider the consequences of the terrain and follow safe travel protocols.
In the mountains around Bozeman and Big Sky, officials say to look for clues to identify areas with recent wind drifting such as cornices, snow stiffening under your feet or sled and shooting cracks as indicators of potential instability. Human-triggered avalanches are possible in wind-loaded terrain and unlikely in non-wind-loaded terrain. Utilize safe travel protocols and thorough snowpack assessment as you travel in or around steep terrain.
The Avalanche Center reports you can ride and ski safely today. Avalanches occur in terrain that is 30 degrees and steeper or areas immediately below these steep slopes. Utilize an inclinometer and measure slope angles frequently.