Bulletin d’avalanche

Southeast Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

Thu
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Wednesday will be the last day to take advantage of current conditions before the avalanche danger begins to rise later this afternoon. Large slab avalanches failing on old weak snow near the ground remain possible today, with evaluations about the snowpack and avalanche terrain being required to manage this problem. New wind slabs will begin building this afternoon with the arrival of increased winds and the next storm. 

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    With a little bit of fresh snow available for transport and winds increasing this afternoon, fresh wind slabs will be a growing problem headed into Thursday. These small slabs may become sensitive to triggering when they are only a few inches thick, as they will be forming over persistent weak layers. Keep an eye out for this avalanche problem on freshly wind-loaded terrain near ridgelines and cross-loaded terrain features. 

    If you can't see your buddy through blowing snow, it's a clear sign that fresh wind slabs are building. 

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    Storms this month have built thick and hard persistent slabs over a widespread weak layer of facets and faceted crusts. These slabs are generally 2 to 3-feet thick. The vast majority of avalanche activity this month has occurred on west to north to southeast aspects, with only a few avalanches from alpine south to southwest facing alpine terrain. Persistent slabs are notorious for erratic feedback and unusual behavior, such as remote triggering and wide propagation. To reliably avoid the problem, choose routes that keep you off and out from under terrain steeper than about 30 degrees that hold old, weak snow near the ground. In steeper terrain, you can reduce your chance of triggering an avalanche by avoiding trigger points where the snowpack is thinner than average.  Thin spots are most common in wind-affected terrain or near rock bands or vegetation.  

    This persistent slab avalanche wrapped from shady to sunny aspects and broke on weak layers near the ground. This a good example of the potential size and widely propagating behavior of our current persistent slab problem. 

Avalanche Discussion

We've been talking about how the persistent slab avalanche problem has become stubborn to trigger for some time now. That was evident with the decrease in signs of instability, avalanche activity, and test results. Though the snowpack structure remained poor, and the potential to trigger a large slab avalanche remained. Now that snowpack structure has also begun to change. The exceptionally cold temperatures over the last week plus, have allowed the faceting process to continue to eat away at the snow surface and the mid-pack slab. We started to observe this structure last week, and it has become more evident in the last couple of days. What this means for the current moment is the continued slow decrease in the likelihood of triggering a persistent slab avalanche and conditions that match the current avalanche danger level with "heightened avalanche conditions on specific terrain". 

Looking ahead, we are starting to move out with the old problem and in with the new problem, particularly on old bed surfaces and at lower elevations where faceting has run rampant. The current snow surface has become weak and faceted again in many areas and as more snow accumulates on this interface in the coming storms we will be building a new persistent slab problem. We will first see this change with growing wind slabs this afternoon and into tomorrow. Those slabs will be failing on the current weak snow surface. After tonight, much of the alpine will be blown to bits and probably see more wind erosion than wind loading. While, we may see wind-loading and new slab growth in unusual places such as below treeline elevations headed into tomorrow. 

Wednesday will be the last day to take advantage of current conditions and some good riding. By later this afternoon the avalanche danger will begin increasing with the arrival of the Arctic Blast. Conditions will be very different by tomorrow morning.  

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