Avalanche forecast

Southeast Mountains

Crested Butte Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Two serious accidents over the weekend illustrate the snowpack's potential for dangerous surprises.  In the Southeast Mountains, avalanches are easy to trigger near and above 11,000', especially in wind-drifted terrain.   A tricky layer of surface hoar buried 1 to 2 feet deep has been the culprit in much of the recent avalanche activity.  Conservative terrain choices will help you manage the problem.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2.5

    A new round of weak layers was buried on February 2nd. These weak layers consist of widespread surface hoar and facets on most east, north, and west-facing slopes, and along with some faceted crusts on higher elevation southerly aspects. Slabs 1 to 2 feet thick over these weak layers continue to be triggered by skiers and riders. This avalanche problem can be remotely triggered from flat terrain, or may propagate further than expected.  Shooting cracks or collapses are a clear sign of danger, but these obvious signs of instability will not always show themselves before an avalanche releases.  There is also a lower likelihood potential to trigger older, larger slabs on weak layers deeper in the snowpack, most likely from shallow terrain features or step-down avalanches.  

     

    A recent skier triggered persistent slab on Coneys that likely failed the layer of surface hoar that is now buried 1 to 2 feet deep.  

Avalanche Discussion

We continue to find evidence of easily triggered persistent slabs and dangerous avalanche conditions in parts of our forecast area, evidenced by the endless streak of human-triggered avalanches, along with numerous shooting cracks and collapses observed yesterday (ex. Mt. Emmons, Washington Gulch).    The most reactive conditions are associated with our buried surface hoar layer and appear to be worse in the swath of terrain near or east of our forecast zones boundary.  Those are the areas that missed out on the Ruby Range slammer on February 3rd but have subsequently seen more favored snowfall and/or wind drifting from our most recent storm (February 7-8).  In these areas, slabs are most developed as you gain elevation towards 11,000', especially in wind-drifted terrain.  The recent strong inversions are starting to decay slabs below treeline, especially below 10,000' in the Southeast Mountains, which is helping the snowpack quiet down at those lower elevations.   

What is the deal with surface hoar, and why are we still getting daily human-triggered avalanches?  This article explains more about this fragile weak layer, which was unusually large and widespread on west to north to east aspects when it got buried at the beginning of the month.  Unlike the near-surface facets or "recycled powder" that are more commonly buried during mid-winter dryspells, surface hoar grains are larger and remain weaker for longer periods, all other things being equal. This layer will continue to plague us for a while. The size of the layer varies widely from basin to basin, and is hit or miss because of previous destruction from wind, sun, or early sluffing at burial time.  All of the avalanche accidents in the past week have involved our buried surface hoar layer.  Not all slopes have the issue, but a prudent approach right now is to assume it is there and make decisions based on the presence/absence of a slab and the resulting terrain consequences if you trigger the problem.  

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