Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

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

Avalanche conditions are dangerous at higher elevations.  Increasing winds later today will continue to form sensitive wind slabs and stress recently buried weak layers a few feet deep on wind-loaded slopes. This video summarizes the situation.   Although avalanche conditions are less dangerous at lower elevations protected from the wind, stay cautious: a skier was caught and carried in a 2-foot slab below treeline yesterday near Camo Glades.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    Snow and wind-loading in the past week have formed a new generation of slabs up to several feet thick over small-grained facets in the upper snowpack.  Numerous natural and triggered slabs have occurred on this layer in the past few days.  Slabs are larger and most sensitive near and above treeline on wind-loaded slopes, especially on colder aspects.  Give leeward terrain a cautious buffer by choosing lower slope angles or smaller terrain features, while staying alert for potential instabilities on wind-sheltered terrain.  

    On unusually shallow slopes, most commonly in the Southeast Mountains, there is still a small potential to trigger a destructive avalanche that breaks on deeper weak layers. The most concerning structures are on northerly aspects near and above treeline where snow depths are less than 170 cm.  

  • Wind Slabs

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

    About 6" to 10" of recent snow and increasing southwest winds today will form sensitive drifts on leeward terrain features at higher elevations and build on wind slabs that formed yesterday.  Look for wind slabs forming below corniced ridgelines and in crossloaded gullies.  Blowing snow and cracking in the snow are signs of danger.  Wind slabs could be dangerous by themselves in high-consequence terrain, or they could step down and trigger a larger persistent slab avalanche described above.  

    A recent wind slab avalanche on Augusta. 

     

Avalanche Discussion

With winds decreasing overnight, active loading has paused and we should see a slight downturn in the sensitivity of problems this morning.  Winds increase later this afternoon and go on a 36-hour run with a refresh in transportable snow tomorrow.  This will increase the threat of natural activity again on windloaded slopes, similar to this large natural avalanche that ran yesterday on Mt. Owen.  Over the past few days, we've seen a steady stream of natural and triggered slab avalanches breaking on mid-March facets and faceted crusts, now buried about 18" to 3 feet deep.  Most of the activity has been on windloaded slopes where slabs are thicker and denser.  Yesterday's skier-triggered avalanche near Camo Glades highlights the potential for issues below treeline as well, particularly in the Northwest Mountains where snow totals in the past week are larger.   

Instabilities involving our new and developing persistent slab problem have been hit or miss, depending on the presence and absence of slab and weak layer.  So how to manage today's issues?   Start by avoiding steep wind-loaded slopes:  Slabs there are dangerously large and have shown a clear pattern of being problematic.  Wind sheltered, southerly aspects don't appear to have buried weak layer issues and will offer dry powder turns this morning until warming temperatures and/or hits of sunshine create shallow wet loose concerns.  On the north side of the compass below treeline, pause to assess the snowpack for instabilities in the upper two feet of the snowpack.  Quick stability tests can help identify potential issues.  Below treeline slabs are better developed and more of a concern in the favored Northwest Mountains, while most slopes below treeline in the Southeast Mountains lack sufficient recent storm totals for issues until you climb to about 11,000'.   When in doubt, choose smaller and less consequential terrain or lower slope angles.   

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