Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Thu
Alpine
4 · High
Treeline
4 · High
Below
4 · High
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Highlights

An Avalanche Warning is in effect today.  Multiple feet of fresh snow on a weak foundation has created very dangerous avalanche conditions.  Observers yesterday easily triggered avalanches that broke wide distances or were remotely triggered from flat terrain.  With storm totals doubling since then, avalanches will be even larger and more destructive.  The natural avalanche cycle will continue until windloading and snowfall let up.   Travel in and below avalanche terrain (slopes steeper than 30 degrees) is not recommended.  This avalanche terrain map highlights opportunities for safer travel in simple (green) terrain.   

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1.5–2.5

    Heavy snowfall and wind loading have formed slabs several feet thick over weak facet layers in the lower snowpack.  Yesterday's observations of widespread shooting cracks, collapses, and triggered avalanches highlight how sensitive these slabs are to human and natural triggers.  Expect challenging avalanche behavior, characterized by avalanches connecting across terrain features and triggered remotely from near or below steep slopes.  The most problematic slopes face west, north, and east: avoid traveling on or under slopes steeper than 30 degrees on these aspects to avoid the problem.  

  • Storm Slabs

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

    Even on slopes without well-developed persistent weak layers, you will need to manage for storm slab instabilities.  Storm slabs will be larger and potentially more sensitive on wind drifted slopes, where you may encounter poor bonding to old crusts on southerly aspects or on mid-storm weak layers.  The storm snow will generally be less reactive on low-elevation, southerly slopes that were bare at the start of the storm. However, monitor for mid-storm layer instabilities in terrain where vegetation and ground roughness are now obscured.  

    An example of a storm slab on a small test slope.  

Avalanche Discussion

Avalanche danger is peaking this morning at the tail end of the atmospheric river event. Since Monday night, 2 to 4 feet of snow (2.3" to 3.4" SWE) has rapidly accumulated on our well-described shallow and weak snowpack. Yesterday, evidence of an unstable snowpack on our old snow layers was glaringly obvious: every single observation reported widespread collapses, cracking, and remotely triggered avalanches.  Today's avalanches will be larger and more dangerous.  Natural activity will start winding down below treeline once snowfall ends sometime this morning, while shifting winds today will continue producing naturals at higher elevations through the day.  Our snowpack is going through its early-season growing pains, and the danger is flashing red, but here are some reasonable ways to reduce your risk:

  • Head on over to opening day at CBMR, where patrol is diligently working to mitigate the hazards.
  • Choose low slope angles less than 30 degrees without overhead hazards. Overhead hazards are expected to be mostly D2 to D2.5 in size, with the potential for a few D3 outliers in the Ruby Range or from our largest/longest-running terrain features.  
  • Travel on those below treeline, southerly slopes that were dirt and grass a week ago, while monitoring for the threat of any mid-storm instabilities if you can't see sage bush poking through the snowpack.  Sure, you'll probably scrape a few more rocks but that's way better than getting swept away in a widely propagating avalanche that breaks on old, weak snow layers on other aspects.
  • Put on your favorite Christmas movie (Zach's picks: Elf, Love Actually,  or Bad Santa if you're feeling a little risky) and start basting that turkey. The danger will gradually subside, although we'll need to use a conservative mindset through the holiday weekend with our persistent slab issue.   

Regions covered