Fresh wind drifts and persistent weak layers buried near the base of the snowpack may result in human-triggered avalanches. Select smaller, lower-consequence slopes free of terrain traps such as trees and cliffs. Before traveling in avalanche terrain, evaluate the snowpack for instability due to buried weak layers and avoid recently wind-loaded areas where shooting cracks and a hard, drum-like surface indicate potential instability.
Moderate to strong winds are gusting at all elevations in the Bridger Range. Watch for unstable fresh drifts on mid-slope rollovers or other less commonly wind-loaded features, as well as near upper elevation ridgelines.
In the Bridger Range the persistent slab problem is less widespread than elsewhere in our forecast area, largely due to most of the early season snow melting instead of becoming weak. Before entering avalanche terrain, dig to look for the weak snow near the ground and adjust your plans if you find signs of instability.
Another day, another persistent slab avalanche breaking on weak layers near the ground. Yesterday, snowmobilers triggered a large avalanche below Chimney Rock, north of Cooke City, and a local guide saw a slide that broke widely across Airplane Bowl in the Lionhead area.
The focal point for recent avalanche activity and signs of persistent slab instability has been in the southern ranges (S. Madison, S. Gallatin, Lionhead, Island Park, and Cooke City) at middle- and upper-elevations, where recent avalanches have broken 300 up to 5000 feet wide and 2-6 feet deep, with one up to 12 feet deep in Cooke City (Taylor Fork avalanches, Tepee Basin avalanches, earlier Scotch Bonnet avalanche). Recent slides on Buck Ridge and Lone Lake Cirque in the Northern Madison Range, along with snowpack observations, demonstrate that this problem extends beyond the southern ranges where it is most likely.
Winds continue to drift snow, especially in the Northern Gallatin and Bridger Ranges, where wind slab avalanches are a concern at all elevations. As snow surfaces harden, instability becomes less likely, but it could still surprise a skier or rider with a nasty ride. Further south in the mountains near West Yellowstone, Island Park, and Cooke City, wind loading and associated instability are more restricted to upper-elevation terrain below corniced ridgelines and gullies.
Dangerous and tricky avalanche conditions exist in the Southern Madison and Southern Gallatin Ranges and the Cooke City, Island Park, and Lionhead areas. It is unlikely that you will get clear signs of instability, like the groups of riders in Red Canyon and Two Top who heard loud whumphs as weak layers collapsed. However, deadly, human-triggered avalanches on steep slopes are likely, and the danger is CONSIDERABLE. Avoid travel on or immediately below slopes steeper than 30 degrees, or you are simply rolling the dice.
In the northern portions of the advisory area, including the Bridger, Northern Madison, and Northern Gallatin Ranges, human-triggered avalanches are possible, and the avalanche danger is MODERATE. Follow safe travel practices and select smaller, lower-consequence terrain free of traps like trees and cliffs. Evaluate the snowpack for instability due to buried weak layers using an extended column test, and avoid recently wind-loaded terrain where shooting cracks and a hard, drum-like surface may indicate instability.
