Togwotee Pass

You’re most likely to trigger an avalanche on recently formed drifts of wind-blown snow that may be sensitive to the weight of a skier or rider. While less likely, it is also possible to trigger an avalanche on older weak layers buried 2+ feet deep in isolated terrain features in shallower areas. These layers are not widespread, however, the resulting slide will be larger. Avoiding thinner areas in the snowpack at middle and upper elevations is one way to reduce your risk. 

The interplay between slabs and weak layers is phenomenally complex. Generally, the weight and the characteristics of the overlying slab affect the development of a weak layer after burial. In the Tetons, weak snow and crust+facets have been buried beneath a 3+ foot thick slab of snow for many weeks now. During this time, the weak snow has been mechanically compacted by the weight of the overlying slab. In addition, deeper snowpacks tend to create conditions where faceted grains in the snowpack can round and gain strength. Because of this, we saw signs of healing and dormancy. The snowpack in the Greys River and at Togwotee pass has remained thinner and weaker throughout the season and has shown consistent activity with larger loading events. With the addition of continued snowfall, the complex relationship is starting to show a different balance in the instability-stability dance, and this is worth noting as you travel in the backcountry today.

If you travel to regions of the Greys River or Togwotee, the slab overlying the weak layer is thinner and the weight has not been enough to significantly change the properties of the weak snow. Since the snowpack has remained thin, strong gradients in the snowpack have helped weak layers remain weak. from complications due to the nature of the loading. Instead of putting one big load of snow on at once and giving the weak layer time to adjust, we have gradually built a slab in small doses.

Wind-loading: A foot plus of recent snowfall over several days and the light to moderate winds have probably loaded some exposed slopes. Slopes with stiffer snow near the surface—whether from wind-loading or "spin drifting" below large cliff faces—are more likely to produce big avalanches than areas where the surface is loose powder.

Likely trigger points: You are most likely to impact deeper weak layers on certain aspects and on parts of a slope where the snow cover is thin, like near rocky outcrops. Heavily wind-affected areas where the wind created a complex pattern of scoured and loaded slopes are also more likely to be problematic.

Slope angle: Avalanches are most likely on slopes around 35-45 degrees in steepness. However, remember that persistent slab avalanches can be triggered remotely: from gentler terrain below or to the sides of steeper slopes.

As an aside, we are grateful as a community that all parties escaped relatively unscathed from human-triggered events yesterday.