Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 3 years ago.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

Highlights

It will be possible to trigger an avalanche 2-4 feet deep in steep wind loaded terrain at the upper elevations. Carefully evaluate the snowpack or stick to low angle terrain today. In addition, be on the lookout for drifted snow in the upper elevations as winds pick up today.

Avalanche problems

  • Persistent Slabs

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

    Snowfall over the last week has created slabs 2-4 feet thick. The recently formed slabs are sitting on weak snow in the upper elevations. These slabs have proven themselves to be most reactive in steep, wind loaded terrain on the north half of the compass. While instability on this interface peaked 4-5 days ago during a natural avalanche cycle, multiple human triggered avalanches occurred just two days ago. These events indicate that the snowpack is still adjusting to the most recent load in some locations. Approach steep terrain in the upper elevations with suspicion. Extra caution is advised in exposed, wind affected terrain that is punctuated by rocks and cliffs. Obvious signs of instability such as collapsing may or may not be present. As a result, it is important to make your own stability assessment of a particular slope before committing to steep terrain. If you are unsure about a stability assessment, then defaulting to lower angle terrain is always a good call.

    Additional Discussion

    Increasing winds out the west today could build shallow slabs in upper elevation leeward terrain. Be on the lookout for wind affected snow on the surface that is stiff or drifted. Wind drifted snow that is deeper than 6” is a red flag. A small avalanche that breaks in wind drifted snow could trigger a larger one that fails on the most recent interface.

    A skier triggered avalanche that occurred two days ago (2/10) on the west side of the Tetons.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Weak snow that formed during a prolonged dry period in December remains a lingering threat. Reactivity on this layer is approaching a dormant phase, but is not there yet. Last week’s storm brought a significant load to the mountains and stressed this weak interface. Very large avalanches involving weak snow from December are most likely to occur when an avalanche breaking in the newest snow “steps down” to the January 4th weak layer. This scenario occurred two days ago on the north face of Rendezvous Mountain. If triggered, these avalanches could break 3-5 feet deep and would be unsurvivable if one were to get caught, carried, and buried.

    A large avalanche that was remotely triggered two days ago (2/10) on the north face of Rendezvous Mountain. The avalanche below the cliff band was triggered when it was impacted by the upper slide and stepped down to weak layers deeper in the snowpack.

Avalanche Discussion

Spatial variability is a term that avalanche professionals like to use frequently. When talking about avalanches, it often means that stability can vary significantly in a small geographic area due to subtle changes in aspect, elevation, slope angle, and snow depth. This describes the current avalanche problem nicely. Last week’s storm brought a significant load to the mountains in a short period of time (2.5-4” of SWE). In some locations, such as sheltered/sunny aspects, the new snow is bonding well to the old snow surface. In other spots, namely shady/wind affected terrain, the snowpack is taking longer to adjust. Recently triggered avalanches are evidence of this. Variability in stability means that it is important to make your own assessment of the snowpack before committing to steep terrain. Digging down to the most recent interface can be helpful, but also noting the characteristics of the terrain where you are riding is important. Red flags include the following.

  • Windy. Is there evidence of wind loading? Does the terrain seem exposed to wind?
  • Steep. Is the terrain above 35 deg? Does it roll over?
  • Shaded. Nearly all of the recent avalanches have occurred on slopes with a northern tilt.
  • Rocky. Again, many of the recent avalanches have occurred in areas that are rocky or above cliff bands.

The interface that was buried on 2/2 was created by a week of warm, relatively dry weather. As a result, the weakness is not profound or widespread. The snowpack simply needs more time to adjust and stabilize. Continued vigilance and conservative terrain choices are recommended over the next few days.

Regions covered