Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

On some terrain features, it remains possible to trigger an avalanche that breaks up to several feet thick on weak snow near the ground.  Previously wind-loaded slopes that face north or east are most concerning.  Carefully assess the snowpack for dense slabs over weak snow, and consider the potential consequences before riding in avalanche terrain.

Avalanche problems

  • Persistent Slabs

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

    Slabs 1 to 4 feet thick have formed over several persistent weak layers in the snowpack:  Weak facets and depth hoar near the ground and surface hoar layers in the upper snowpack. The problem has been most active on northerly and easterly facing slopes, with some avalanches on westerly facing terrain as well. Persistent slabs have become difficult to trigger and signs of instability are infrequent, but if you cross the wrong slope or the wrong spot on a slope, a single collapse can result in a surprisingly large avalanche involving most of the snowpack.  Persistent slabs could break wider than you expect, and they can be triggered from flat slopes connected to steeper terrain above you. You can reduce your risk by traveling on slopes where the problem isn't highlighted above, or by traveling on small terrain features without terrain traps.  You can avoid the problem on slopes consistently less than 30 degrees. 

     A very large natural avalanche on an east-facing slope of Treasury Mtn that likely ran on 12/10.  This is the most recent persistent slab observed in the Northwest Mountains.  

Avalanche Discussion

We're bobbing in a sea of yellow as our well-advertised weak layers slowly adjust to the major loading events earlier this month.  The only exception to Moderate danger is below treeline in the Southeast Mountains, where, at a zone-wide scale, the problem is relatively small and isolated across the terrain.  The danger is Low there because slabs are thinner and have been quicker to adjust.  You're most likely to find lingering instabilities along the border of our two zones, in areas like Snodgrass (see this ob), or on a slope that was previously drifted.  

The recent mild temps and lack of significant loading are also helping the snowpack slowly adjust elsewhere.  It's just a slow and steady process that takes time.  Our visualization tools illustrate the decline in avalanche activity and signs of instability this week (Scroll down to the bottom two graphics).  We want to emphasize that our most recent avalanches last Sunday (Schuylkill Ridge, Treasury Mtn) would have been difficult to survive.  As the likelihood decreases, the size remains the same: the conundrum of a snowpack plagued by persistent slab issues.  If you aren't interested in this lower likelihood but consequential scenario, the low angle is riding great right now and steep southerly aspects are also a more trustworthy option (except for high southeasterly slopes).  If you are stepping out into the suspect northerly or easterly aspects where our buried weak layers are lurking, you can reduce your risk on smaller slopes with clean runouts.  Slopes that ran naturally earlier this month are a safer option.  Previously drifted slopes with variable snow depths and/or rock bands tend to be the most problematic as time goes on.  Focus your decision-making on the consequences if something goes wrong, and practice sound travel habits like traveling one at a time in avalanche terrain.  

Alpine winds increased to transport speeds last night out of the north.  With only a few inches of snow available for transport, wind slab formation will be relatively minor.  However, don't get caught by surprise if you kick off a thin wind drift in high-consequence terrain.  

The Fireside Chat series kicks back off this Saturday 12/16. Here is more info. We hope to see you there!

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