Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

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Alta quota
2 · Moderato
Limite del bosco
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Sotto il limite
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In sintesi

The chance of human triggering a slab avalanche has notably decreased from earlier this month, but the consequence if caught in one of these avalanches remains deadly given the potential avalanche size. If you are riding in avalanche terrain today, consider ways to reduce your chance of triggering the avalanche problems. One way to decrease your chance of triggering an avalanche would be to seek out areas with snow depths greater than 150 cm(5 feet) that are protected from the wind and riding slope angles less than 35 degrees.

 

 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3.5

    Slabs ranging from 5 to 8+ feet thick have formed around much of the compass and at all elevations over faceted weak layers in the lower snowpack. These weak layers have adjusted to their current load and have become more difficult to trigger. The most suspect areas to release this avalanche problem would be trigger points and areas where the snowpack thins to a below-average depth. Such as near rock bands, on some slopes that previously avalanched and have refilled, or where winds have formed variable snow depths. Persistent slab avalanches can propagate widely through the terrain, or be remotely triggered from low-angle slopes connected to steeper slopes. You can reduce your risk by traveling on slopes with a deep, uniform snowpack, and you can reliably avoid the problem by traveling on slope angles that are consistently less than 30 degrees and not connected to steeper terrain above.  

     

     

    1/4:  A destructive natural avalanche in Red Lady Bowl broke full-width last week.  This avalanche would be hard to survive.

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1–2

    Wind slab that formed last week is healing and have become more stubborn to trigger. While unlikely to release, it will be important to recognize this avalanche problem if you are riding on steep wind-loaded terrain where a low likelihood problem would have a high consequence outcome. Keep an eye out for convex wind-loaded terrain features and consider routes to avoid those specific features. 

    This large wind slab failed on Mt. Emmons on January 12th.

Avalanche Discussion

Over the last several weeks the snowpack has grown significantly with continuous snow storms. During this time the snowpack has become stronger, but weak layers needed time to adjust to this continuous loading. We are now seeing that break in loading. Yesterday's warmup kept the avalanche danger elevated, and now we are seeing the avalanche danger decrease before the next series of storms.

The NW Mountain forecast is now characterized by a low probability but high consequence persistent slab avalanche problem. The upper snowpack is relatively strong, mid-pack weak layers are healing, but the well-developed weak layers near the ground are still problematic. To upset those deeper weak layers, we would generally need to see a large load, or somewhere the overlying slab thins and snowpack height decreases, creating an area where the weight of something smaller could impact those layers. It's important to realize that the resulting avalanche would likely be very large, destructive, and probably deadly. Back to the low-likelihood high-consequence conundrum. 

The SE Mountain forecast area continues to have a CONSIDERABLE avalanche danger rating today. In contrast to the deeper snowpack in the NW Mountain forecast, the SE Mountain forecast has a shallower snowpack with thinner slabs. There are more locations for smaller loads such as a human to affect those weak layers near the bottom of the snowpack. At below treeline elevations, we have seen a break in the loading on those weak layers and they have had more time to adjust to their load. This has allowed the avalanche danger to drop at that elevation. The near treeline and above treeline elevations have seen the loading events continue the longest, through wind-loading, and the persistent slab avalanche problem is expected to remain the most sensitive to triggering in these locations. 

Looking ahead to the next storm, the avalanche danger will primarily be driven by new snow avalanche problems, before we see enough snow accumulate to begin increasing the likelihood of triggering the persistent slab avalanche problem. 

Regioni coperte