Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 2 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The avalanche danger may rise throughout the day as new snow and wind create sensitive fresh slabs in exposed terrain at the mid and upper elevations. Additionally, triggering an avalanche 1-3 feet deep that fails on buried weak layers is a real possibility. Carefully evaluate new snowfall amounts and consider conservative terrain choices as buried weak layers may be stressed by additional weight today.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–1.5

    Snowfall is beginning to develop in the mountains this morning with 6-10” of new snow possible by this evening. Westerly winds with speeds averaging in the teens (mph) could form new soft slabs up to 14” thick in wind-loaded terrain at the mid and upper elevations. These slabs will be deepest and most sensitive to triggering on slopes where the wind has created fresh drifts. Watch for signs of wind-loading including blowing snow, dense drifts, and smooth or rippled textures. Cracking is a good indication that you have found unstable snow. These soft slabs will likely only involve today’s snowfall, however, it is possible that a surface slab could step down to deeper weak layers resulting in a large avalanche.

  • Persistent Slabs

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

    Weak snow in the lower half of the snowpack exists in the majority of terrain above 7,500’. In the upper elevations, hard slabs up to 3 feet thick lie upon this weak snow. Hard or soft slabs 1-2 feet thick in the mid elevations also sit on weak snow and are most likely to be triggered in terrain on the north half of the compass. South facing slopes that were bare ground prior to Dec 15th hold a generally more stable snowpack. The likelihood of triggering a persistent slab could increase as additional snow (weight) is added today. Slabs triggered on the surface could step down to the weak snow near the ground resulting in a large avalanche.

    Recent avalanches, cracking, and collapsing are obvious signs of unstable snow. These signs may or may not present themselves prior to triggering an avalanche today. Hard slabs in the upper elevations can break above a person and propagate long distances across slopes, making escape difficult. Remote triggering is becoming less likely, yet with additional loading today, it is not out of the question. Therefore, it is still worth considering the terrain that lies above you while traveling in the backcountry. Digging below the snow surface is a great way to observe/test where weak snow exists. However, seeking out low angle terrain remains the best way to avoid triggering an avalanche if you are uncertain about the structure of the snowpack where you are skiing/riding.

    Natural avalanche on Taylor Mountain. NE-E facing @ 10,000'. Most likely occured late 12/18 or early 12/19 during peak winds. This avalanche failed on weak snow grains near the base of the snowpack.

    Photo: Bridger-Teton Avalanche Center

Avalanche Discussion

There is a fair bit of uncertainty associated with today’s forecast. Snowfall is just starting as I write and the amount of new snow that the Tetons will receive today is unclear. If we receive the upper end of forecasted amounts, in the 10”/.5” SWE range, then triggering an avalanche in wind-loaded terrain at the mid and upper elevations may become likely. This will also be enough of a load to increase the sensitivity of the persistent slab problem, especially where these two problems overlap. With collapses being reported in shady terrain around Teton Pass as recently as Dec 21st, it is unlikely that the snowpack in these locations will respond well to any significant loading taking place today.

If today’s storm only produces several inches, then the avalanche hazard will remain steady with human triggered avalanches possible in steep terrain where the persistent slab problem exists (see above). Carefully evaluate new snowfall amounts and wind as you travel today, and remember that triggering an avalanche on weak snow near the base of the snowpack is still possible in many locations regardless of how the forecast pans out. Given today’s uncertainty it is best to make conservative travel plans and be ready to adjust your route/objectives accordingly.

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