Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

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 3+ 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. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    New snow from the past 48 hours holds the possibility to remain sensitive to triggering today, even with decreasing winds. Periods of consistent snowfall make for great riding, however,  each brief clearing or change in temperature and/or wind flow creates a different interface and different new-snow slab to think about.

    Yesterday saw multiple reports of human-triggered avalanches. Most of these failed within the newest snowfall and were in upper-elevation, leeward terrain, and will likely be one to two feet in depth.  With a foot plus of recent snowfall, the light to moderate winds have probably loaded some exposed slopes. In alpine terrain, you may find some fresh drifts and wind slabs that demand respect on their own. 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.

     

     

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1–3

    Over the past week, we've been seeing more and more propagating results on middle and upper elevation aspects ranging from east-south-west across the compass. With a consistent trickle of snowfall, it can be hard to determine when the slab recipe reaches a tipping point with a weak layer.  At middle and upper elevations, snow from early November is buried underneath a dense, 3+ foot thick slab of settled snow. An additional layer of weak snow was buried in early December. Both of these layers have shown reactivity in the past week. We can see that the snowpack structure isn’t great in these areas and has remained so throughout the season, but we can’t predict exactly when or where you might affect the weak snow underneath.

    Trigger points are an important consideration with these avalanches. You can reduce your chances of awakening a larger dragon by avoiding slopes with shallow snowpacks and more southerly aspects where you can more easily impact the weak layer. Trigger points are most common in alpine (or alpine-like) terrain: very steep (over about 35 degrees), rocky, and wind-affected. Pay attention to what's below you—look for trees, rocks, gullies, and other terrain traps. 

    (1/16/2023)

    This avalanche was triggered by skiers on a west aspect off of Albright Peak around 10,000'. It failed on weaker snow deeper in the snowpack. A trend towards reactivity on these layers has been starting to show on shallower upper-elevation aspects. 

Avalanche Discussion

One avalanche does not create a trend. However, over the past week, we've seen a re-awakening on both the November and December facet layers in upper elevation terrain ranging from east-south-west on the compass. To my mental model, this does create a trend and a difficult-to-assess one at that. My suspicion is that yesterday's avalanche on Albright has some sort of crust+facet combination at play, but we hope to confirm this today.   

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. 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. 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. The ingredients have remained with us throughout the season, and currently, the recipe is set up in isolated areas. The Teton trickle has made for great skiing this year; however, complications due to the nature of that loading exist on the aforementioned aspects. Instead of one larger load of snow on at once and giving the weak layer time to adjust, we have built a slab in small doses. Dependent on the weak layer and its location, this type of loading can make the line between dormancy and reactivity harder to infer as a rider and help a weak layer stay reactive for extended time periods. 

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. 

Regions covered