Northern Gallatin Range

While the likelihood of triggering an avalanche has decreased since last week’s snowstorm, they remain possible on slopes where 10” or more of snow is sitting on a weak faceted interface and strong winds are building unstable slabs on wind-loaded slopes.

Spatial variability is a challenge, but slides are most likely on shadier aspects with well-preserved weak layers and the added weight of dense wind-drifted snow. If you plan to ski and ride in avalanche terrain, put your shovel in the snow to evaluate for instability and choose smaller slopes where avalanches would be correspondingly smaller, and those with clean run outs and fewer terrain traps, such as trees, cliffs, and gullies.

Human-triggered avalanches are possible on steep slopes where 10” or more of snow from last week’s storm rests on a weak layer of sugary facets and surface hoar. Persistent slab avalanches are most likely where there is the added weight of dense wind-drifted snow, on shadier aspects with well-preserved weak layers, and in areas that received a bit more snow last week, such as Cooke City and the Southern Madison Range. Two inches of new snow in the Bridger Range this morning will not significantly change the avalanche danger there.

Spatial variability is a challenge due to the inconsistent distribution and reactivity of weak layers. Many slopes appear stable, but there are some booby traps out there (video). Yesterday, ski guides in the Southern Gallatin Range experienced localized cracking and collapsing on shady slopes (observation), and guides south of Cooke City heard rumors of an avalanche triggered by a group skinning uphill. On Friday in Taylor Fork, a snowmobiler triggered a slide about a foot deep and 100 feet wide (observation and photo), and another rider spotted a fresh natural avalanche (observation and photo). Also on Friday, a slide broke widely across a slope near Cooke City (observation). At Bacon Rind, large collapses and an obvious weak structure were easy to find (observation, video), while just a short distance away in Tepee Basin the day before, no obvious signs of instability were present (observation). In the motorized area of Lionhead, conditions are generally stable, but farther north near Hebgen Lake, a skier triggered a drifted slope that entrained weak snow and ran a long distance down a steep slope (observation).

Generalizations about weak-layer distribution are not a substitute for putting your shovel in the snow to look and for selecting appropriate terrain, but here it is. Crusts cap weak layers on more southerly aspects that generally don’t have sufficient load to start breaking as persistent slab avalanches yet. More northerly aspects (E-N-W) remain weaker and are more likely to avalanche. With more snow coming this week, areas with instability will expand.

If you choose to ride or ski steep terrain, favor smaller slopes where avalanches would be correspondingly smaller, and those with clean run outs and fewer terrain traps, such as trees, cliffs, and gullies. Avalanche danger is MODERATE in the Bridger, Madison, and Gallatin Ranges and in the Cooke City and Lionhead areas.

With less snowfall in the Island Park area last week, avalanches are unlikely, and danger is LOW. Follow standard safe travel practices, carry rescue gear, and watch for isolated and lingering shallow instability.