Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Stable weather without a recent loading event continues to decrease the chances of you triggering a dangerous avalanche.  The most concerning terrain features are leeward slopes near and above treeline.  Feedback from the snowpack like collapsing and shooting cracks is becoming less frequent and sporadic.  Predicting which slopes hang in the balance can be a dangerous game of guessing; if stepping into avalanche terrain is on the menu for you, then choose slopes that offer lower consequences in case you guess wrong.       

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    On or near steep terrain, you can trigger persistent slabs 2 to 4 feet thick that fail on weak snow near the ground.  Persistent slabs often surprise even the most experienced travelers: They give irregular feedback, they can propagate unusually wide distances, and they can be remotely triggered from below or adjacent to the slope.  To avoid this problem,  choose routes that stay off of, and out from underneath, steep terrain holding dense slabs over sugary weak layers.  Poor structure is most common on the slopes highlighted by the distribution rose above, on west to north to east and some southeast slopes.   Shooting cracks and collapses are clear warning signs to stay on slope angles less than about 35 degrees, although their absence isn't a guarantee of safety.   In the Northwest Mountains, slabs are generally thicker and denser: you are most likely to trigger them from shallow points on the slope such as rock bands, pungie trees, or where slabs taper in thickness from wind effects.  

    12/31: A large, remotely triggered persistent slab in Redwell Basin

Avalanche Discussion

The last loading event was about 5 days ago.  This loading event largely impacted leeward terrain features at upper elevations due to northerly winds transporting new snow.  Below treeline slopes received very little snow from this event, only a few inches.  These factors make previously drifted near and above treeline features the most concerning and suspect.  Stability tests and signs of instability are showing improvement, but the evidence does not suggest that slabs are unreactive to the weight of a person or machine.  Predicting which slopes hang in the balance and which slopes have reached a temporary equilibrium is a challenging and complex decision.  A good way to look at decision making for traveling on upper elevation slopes, where you should be certain that slabs exist, is to think about consequences and not likelihood.  Understanding the likelihood of triggering an avalanche on a given leeward slope remains a bit of a guessing game whereas judging the consequences of triggering an avalanche is a bit more straightforward.  If you are uncertain about the chances of triggering an avalanche on near and above treeline slopes then consider the consequences of being wrong.  Are there terrain traps like trees, cliffs, or gullies?  Is the slope large and offer the potential for a long-running avalanche?  Your best tool for managing uncertainty is with thoughtful terrain selection that leaves room for error.

The above logic applies to below treeline slopes where you find cohesive slabs resting above weak snow.  Many below treeline slopes in the Northwest Mountains contain the recipes for an avalanche; cohesive slab and weak layer.  As you move closer to town or further east, the Southeast Mountains, slabs have been degrading due to the faceting process.  Less snowfall in the Southeast Mountains created a thinner and less dense slab that is more susceptible to decay from cold temperatures.  This process is changing below treeline slopes in the Southeast Mountains towards the "unlikely" end of the spectrum for slab avalanches.  The places where you can find a slab avalanche problem is becoming isolated.  The danger rating for this below treeline part of the zone remains at MODERATE for today but is expected to move to LOW for Tuesday. 

Regions covered