Cooke City

Very large, human-triggered and natural avalanches breaking 2-5 feet deep on weak layers near the ground have been a daily occurrence, with thirty-four slides reported from Cooke City in the last week. The only sustainable strategy right now is to minimize or eliminate your exposure to slopes steeper than 30 degrees. Careful and conservative route-finding is essential. Conditions are less touchy at lower elevations, where weak layers are less widely distributed.

The primary avalanche concern throughout the forecast area is persistent slab avalanches failing near the ground on weak layers formed when snow from October and early November storms transformed into weak, sugary facets, which were then loaded by storms beginning around Thanksgiving.

COOKE CITY

Very large, human-triggered and natural persistent slab avalanches breaking 2-5 feet deep have been a daily occurrence in the mountains around Cooke City, with thirty-four slides reported in the last week (avalanche observation page). Yesterday, local guides described a powder cloud from a natural avalanche south of town, a cornice fall, and a large whumphing collapse (details). On Saturday, a snowmobiler triggered and escaped from a large avalanche on the east side of Henderson Mountain (details and photo). Last Thursday, there was a very close call when a rider was buried, found quickly, and dug up alive (details and media). Watch Alex’s video from Saturday to see a rundown of some of the recent avalanche activity.

The only sustainable strategy is to minimize or eliminate your exposure to slopes steeper than 30 degrees. The danger is CONSIDERABLE at middle- and upper-elevations in Cooke City, where human-triggered avalanches are likely. The danger is MODERATE at lower elevations where weak layers are less widespread.

BRIDGER RANGE   GALLATIN RANGE   MADISON RANGE   LIONHEAD AREA   ISLAND PARK

The odds of triggering a 1-3 foot deep persistent slab avalanche have decreased in the mountains around Bozeman, Big Sky, West Yellowstone, and Island Park, but the fundamental snowpack structure has not changed in the middle- and upper-elevation bands despite the warm temperatures (Mt. Blackmore obs and video, Beehive obs and video). The Big Sky Ski Patrol has intentionally triggered significant avalanches every day for more than a week, clearly demonstrating the potential in similar backcountry terrain. If considering travel on steeper slopes, select lower-elevation terrain where weak layers are less prominent, or find smaller, less-steep pitches free of terrain traps, and evaluate the snowpack for instability. Avoid steep, large, and high-consequence avalanche paths.

At lower elevations, early-season snow did not survive November’s warm temperatures, and a recent series of freeze-thaw cycles makes avalanches unlikely. This also describes the middle elevation band on south-facing slopes in the Bridger Range. 

The danger is MODERATE at middle and upper elevations and LOW in the lower-elevation band throughout the forecast area, other than Cooke City.