Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Dangerous avalanche conditions exist.  More than a foot of denser-than-normal snow has accumulated since Monday night and efficient southwest winds drifted snow to leeward slopes.  You are likely to trigger an avalanche in the storm snow where it has drifted by the wind.  On some isolated terrain, avalanches could break deep in the snowpack.  Avoid leeward terrain to reduce your risk of triggering a dangerous avalanche and in sheltered areas, you need to make a careful snowpack assessment before entering avalanche terrain.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3.5

    Slabs ranging from 3 to 6+ feet thick have formed around the compass and at all elevations over faceted weak layers in the lower snowpack.  The poor snowpack structure produced widespread activity during stormy weather in early January.  Now the problem is becoming more difficult to trigger because the snowpack is adjusting and weak layers are hard to impact.  You are most likely to trigger an avalanche from a shallow area on the slopes, such as a rock band or where wind drifting has formed variable snow depths.  Give yourself a wide margin for error given how consequential the problem is right now.    Persistent slab avalanches can propagate widely through the terrain, or be remotely triggered from low-angle slopes connected to steeper slopes.  You can reduce your risk by traveling on slopes with a deep, uniform snowpack, and you can reliably avoid the problem by traveling on slope angles that are consistently less than 30 degrees.  

    Snowfall since Monday night may bring an uptick in sensitivity to avalanches breaking deep in the snowpack.  Use additional caution during this loading period to avoid getting an ugly surprise.

    1/4:  A destructive natural avalanche in Red Lady Bowl broke full-width last Wednesday.  This avalanche would be hard to survive.

  • Wind Slabs

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

    Over a foot of dense, new snow accumulated and been redistributed by southwesterly winds.  Cracking in the new snow in open areas is a good sign that avalanches in the storm snow are likely.  You can look for smooth, pillowy shapes to help you identify recently formed drifts.  Your safest option is to simply avoid terrain with signs of recent drifting.  Avalanches in drifted storm snow will be large enough to bury and harm you.  

    This avalanche on Mount Emmons failed about a week ago from a bout of wind drifting.  Expect similar potential today if the snowfall forecast verifies. 

Avalanche Discussion

Areas in the Northwest Mountains have accumulated more than a foot of settled storm snow and at Schofield Pass, this storm snow contains over 2 inches of snow water equivalent.  2 inches of snow water equivalent in just over 24 hours is a substantial loading event.  Areas closer to town have seen more modest loads with around 1 inch of snow water equivalent.

More than enough volume has accumulated in leeward start zones, in both the Northwest and Southeast forecast zones, to make avalanches in drifted storm snow dangerous.  Slabs could be several feet thick and produce large avalanches that easily bury you.  Simple avoidance of drifted terrain will go a long way in reducing your risk of triggering a dangerous avalanche.

Avalanches breaking deeper in the snowpack on old weak layers, the Persistent Slab problem, have a different likelihood between the two forecast areas.  In the Northwest Mountains, deep avalanches slowly became harder to trigger prior to this storm as weak layers gained strength and slabs became thick enough to reduce the impact of a backcountry traveler on the snowpack.  Shallower parts of a slope where the slab thins offer an increased risk of impacting deep weak layers.  A rough guide to 'shallower' spots would be less than 150cm, or 5 feet, of snowpack depth.  In the Southeast Mountains, the snowpack is commonly less than 150cm which helps to explain why you are more likely to trigger an avalanche in deeper weak layers.  The chances of triggering an avalanche in old weak layers continue to increase as snowpack depths get closer to 100cm, 3 feet, as it becomes easy for you to impact weak layers through the slab.  This example from lower Cement Creek illustrates the point, where the snowpack was generally around or just below a meter, and produced numerous signs of instability.

Avalanche conditions remain tricky around Crested Butte and if you plan to enter avalanche terrain you will need a sharp skill set and a thoughtful approach to terrain selection to prevent being surprised by a dangerous avalanche.

 

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