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

Westerly winds are continuing to load lee terrain at near and above treeline elevations where dangerous avalanche conditions remain. In wind-sheltered terrain, slab avalanches are becoming more stubborn to human triggers, however, avalanches can still be remotely triggered and propagate widely through the terrain. Yesterday there were reports of two remotely triggered avalanches (1 & 2), and observers continue to find more notable avalanches from last week's natural avalanche cycle. It may be late March, but avalanche conditions are complicated and more similar to mid-winter. Natural and human-triggered avalanches are propagating widely across terrain features while becoming large and destructive in size.

Avalanche problems

  • Wind Slabs

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

    Westerly winds are building fresh wind slabs and further loading persistent weak layers at near and above treeline elevations. A triggered slab avalanche could release in the upper 10 to 20 inches of snow, or step down into more deeply buried weak layers. Complicated avalanche conditions exist in these locations. You can avoid the wind slab avalanche problem by sticking to sheltered terrain and/or avoiding the lee sides of ridgelines and cross-loaded terrain features. 

    A human-triggered avalanche on 3/18, that propagated into a wind-loaded terrain feature, with a triple overhead crown and an unsurvivable avalanche. 

  • Persistent Slabs

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

    Since Monday (3/20), 2 to 3 feet of snow has accumulated on a new round of persistent weak layers. The greatest number of avalanches have occurred on easterly-facing slopes where a collapsible crust exists. Similar conditions can be found on westerly-facing slopes. While on northerly facing slopes these slabs are resting on a layer of near-surface facets. Avalanches on these weak layers are exhibiting persistent slab characteristics with wide propagation and remote triggering. We further can't rule out the low probability that a triggered avalanche further steps down to weak layers buried even deeper in the snowpack, producing a destructive avalanche

    Early warning signs for this avalanche problem are rare. So don't expect much for direct feedback. You can reduce your chance of triggering this avalanche problem by avoiding wind-loaded terrain and limiting slope angles to 35 degrees or less. 

     

    3:23 A pile of natural avalanches ran on Purple Ridge (easterly aspects).  The sharpness of the crowns suggests failure occurred at the tail end of the storm during the second half of Wednesday.  Nearly all of the avalanches pictured here are big enough to bury and kill you.

Avalanche Discussion

The recent storm from Monday, 3/20 through Wednesday, 3/22 deposited a slab that is 1 to 3 feet thick in sheltered terrain and much deeper on drifted slopes. Visibility has been somewhat limited in recent days, but observers have still noted a fairly widespread natural avalanche cycle that occurred during this time. The current wind loading that is now occurring is keeping continued natural avalanche activity possible this weekend.

Widespread storm slab instability in the new snow has mostly settled out, however, concerns remain for continued avalanche activity on the persistent weak layers that are buried under the snow that has accumulated this week. The storm slab avalanche problem has now been changed to a persistent slab avalanche problem. The likelihood of human triggering has thankfully decreased in the big picture, but persistent slab characteristics have developed with wide propagating avalanches and remote triggering. 

A triggered persistent slab could further step down to weak layers buried even earlier this winter. This is most common in the SE Mountain forecast area, but concerns still exist in the NW Mountain forecast area. Avalanches releasing on those deeply buried weak layers have been very large in size, destructive, and unsurvivable. 

Since the middle of March, we have been in a steeping back mindset as avalanche conditions have become complicated, and more unsurvivable avalanches are being documented. We are now entrenched in these conditions. Even though it is late March, this isn't a great time for big spring lines and aggressive terrain choices. 

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