Cooke City

The wind arrived as forecast, and with nearly 10” of new snow as ammunition for drifting, conditions are very dangerous in upper elevations where avalanches will break 1-2 feet deep and widely across wind-loaded slopes. The new snow is adding stress to weak layers in the top 3 feet of the snowpack, making larger avalanches breaking 2-3 deep likely, even in non-wind-loaded terrain. Avoid traveling on and underneath slopes steeper than 30 degrees, especially those with drifts from recent wind-loading. Enjoy the new snow while cautiously selecting routes and making conservative terrain choices.

In the past week, there have been 34 avalanches recorded, 6 people caught, 4 partial burials, 2 full burials, and 1 tragic fatality (avalanche activity log). This was concentrated in the Island Park, Lionhead, Cooke City, and Southern Madison areas, with some spill over into the Northern Madison and Northern Gallatin Ranges. New snow is again adding weight to weak layers in the upper 3 feet of the snowpack, and strong winds are loading slopes. Differences in danger relate to recent snowfall and the underlying snowpack structure.

The storm in Cooke City didn’t deliver quite as much snow as we expected, but the wind arrived as forecast and with nearly 10” of new snow as ammunition for drifting, conditions are very dangerous in upper elevations where wind slab avalanches will break 1-2 feet deep. A good example was the large slide in the Sheep Creek drainage on Monday (observation). We don’t know if this storm will load weak layers to the point where persistent slab avalanches break on many slopes, but we do know that this is not the time to mess with them. The danger is HIGH at upper elevations, where drifting and new snow are loading slopes fastest, and CONSIDERABLE at middle and lower elevations, where more slopes are sheltered from wind. Avoid traveling on and underneath slopes steeper than 30 degrees, especially those loaded by the wind. Enjoy the new snow while cautiously selecting routes and making conservative terrain choices.

In the Island Park, Lionhead, Southern Gallatin, and Southern Madison areas, 5-6” of new snow is keeping persistent weak layers at their breaking point. Over the weekend, many large, persistent slab avalanches broke to a depth of 2-3 feet, catching 6 backcountry riders.  While any slope steeper than 30 degrees is suspect, wind-loaded slopes have an added layer of drifted snow where wind slab avalanches breaking 1-2 feet deep are also likely, as the GVSA Groomer noted in the Taylor Fork (observation). In the Lionhead and Island Park areas and the Southern Madison and Southern Gallatin Ranges, theavalanche danger is CONSIDERABLE. Enjoy the new snow on slopes less than 30 degrees steep, where avalanches are unlikely, while generally avoiding traveling on and below steeper terrain where human-triggered avalanches are likely.

The Northern Gallatin and Northern Madison Ranges received less snow than their southern counterparts and had correspondingly fewer avalanches, but as Ian explains, the snowpack structure is similar, and there are unstable slopes to watch out for where persistent slab avalanches could break 1-3 feet deep (video). With winds gusting to 90 mph in Hyalite Canyon and 70 mph in Big Sky, plan to avoid wind-loaded terrain steeper than 30 degrees, where triggering a wind slab avalanche around a foot deep is likely. Given many variables, conservative travel that avoids avalanche terrain is prudent. If you elect to travel on slopes steeper than 30 degrees, seek out smaller, wind-sheltered terrain free from traps like trees and gullies. Listen for collapsing, watch for cracking, and test the upper 3 feet for instability. The danger is CONSIDERABLE at middle and upper elevations in the Northern Gallatin and Northern Madison Ranges.

A few inches of new snow and strong winds in the Bridger Range make wind slab avalanches possible. Avalanches will generally be small but could reach one foot deep on heavily wind-loaded slopes. Shooting cracks and observing nearby avalanches warn of instability. Consider the consequences of smaller slides in your selected terrain and avoid areas where instability and consequence overlap. In the Bridger Range, the danger is MODERATE at middle and upper elevations, with wind-loaded slopes being the concern, and LOW at lower elevations where there is less new snow and more sheltered terrain.