Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Mon
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Out of date — this forecast expired 6 years ago.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

Yesterday a skier was caught and briefly carried in a large and dangerous persistent slab avalanche on Mt. Axtell.  The group reported no signs of instability leading up to the slide, which highlights a trend we are starting to see now with the snowpack.  Slabs in the Northwest Mountains are becoming more stubborn to trigger and giving less signs of instability.  The likelihood of human triggered avalanches is decreasing, but the consequences remain just as serious.  The slabs are generally 2 to 4 feet thick and large enough to bury you.  And worse, the surprise factor is going up now.  You are most likely to trigger an avalanche from a slope where the slab is thinner - either in parts of the zone where the snowpack is generally shallower, or on parts of the slope where the slab thins due to wind effects.  The problematic aspects remain the same: west through north through east and some southeast slopes.  Careful snowpack assessments and terrain selection are important to avoid triggering a deadly avalanche today.  

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 30 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: Large, remotely triggered persistent slab in Redwell Basin.

Avalanche Discussion

Thank you to the group on Mt. Axtell for sharing their close call yesterday in First Bowl.   Take a minute to read the observation.  It highlights a nefarious characteristic of persistent slabs, which is especially important as the danger continues to slowly trend down: irregular and variable feedback.  Some slopes will behave differently than others due to spatial variability, and because of that, you can easily get surprised.

Our snowpacks are starting to diverge more between the Northwest Mountains and Southeast Mountains.  Make sure you are reading the forecast for the zone that you plan to travel in:  here's the map.  These differences are due to seasonal snowfall patterns that have made for a deeper snowpack in the Northwest Mountains and a shallower one with larger weak layers in the Southeast Mountains.  If you are traveling along the boundary of the two zones (Mt.  Axtell to Mt. Emmons to Gothic Mountain), anticipate a hybrid of the two forecasts. 

We've lowered the danger to MODERATE in the Northwest Mountains.  The pattern here has been for fewer signs of instability over the past couple of days. Slabs are generally thicker and weak layers aren't quite as fragile, making for a lower likelihood but serious consequence problem.   Unfortunately, it can be difficult to identify the specific slopes or specific parts of the slope where you can get into trouble.  The most reliable terrain is slope angles less than about 35 degrees, slopes that face the south quadrant of the compass, and slopes that have previously avalanched.  Otherwise, choosing terrain features with deep and uniform snow coverage helps reduce your risk of impacting and collapsing buried weak layers.  In the Southeast Mountains, the danger remains CONSIDERABLE.   Persistent slabs have been and are likely to continue to be more reactive to human triggers: slabs are softer, thinner, and on more fragile weak layers.  Instabilities are more widespread.   The sensitivity is also trending down, but not as quickly.  Just east of our forecast area in Taylor Park, an observer yesterday reported a "very touchy snowpack, every slope we got on collapsed and would roll through the terrain."  On Snodgrass, observers reported multiple collapses, but more stubborn than in previous days.  Just north of the forecast area in Aspen, there were numerous remotely triggered avalanches up to D2 in size, where their snowpack structure has mirrored our shallower Southeast Mountains.  

These are tricky times with a tricky snowpack.  Bring a conservative mindset to the backcountry today.  

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