Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
Treeline
3 · Considerable
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Out of date — this forecast expired 6 years ago.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

The avalanche danger is slower to decrease in the Northwest Mountains, where storm totals over the weekend were larger.  The threat of triggering an avalanche in the recent snow or on weak layers near the ground is most concerning on windloaded terrain near and above treeline.   Shooting cracks or collapses in the snow are warning signs to choose lower slope angles and less consequential terrain.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    There are two flavors of persistent slabs threatening human triggers, both of which are most common on windloaded slopes where slabs are thicker and stiffer or in parts of the forecast area where recent snow totals were deepest. The youngest generation can be found where recent and windblown snow formed soft slabs over weak facets and faceted crusts in the upper snowpack.  This problem is more reactive and will likely give more reliable feedback such as shooting cracks and collapses where it exists.   The older generation involves stubborn hard slabs that could fail on weak layers near the ground.  Don't expect warning signs from this more destructive problem: the distribution is spottier and feedback is less common.  Persistent slabs can be remotely triggered from below a steep slope or propagate widely across the terrain.  Give yourself a wide margin for error when assessing and managing persistent slabs.

    This soft slab avalanche ran naturally on 1/24. It exemplifies the newest generation of persistent slabs failing on facets and faceted crusts buried in mid-January.

Avalanche Discussion

Despite poor visibility again yesterday, we saw signs of natural avalanche activity continuing.   On Saturday, we observed a handful of human triggered and natural avalanches, breaking on both the storm interface (1/19 layer) and on weak layers near the ground (12/10 layer).   We have shifted this weekend's storm slab problem  into our newest generation of persistent slabs:  instabilities from last week's snow will mostly be localized to terrain features harboring persistent weak layers beneath the snow. This slide that ran yesterday on Red Lady Glades exemplifies our newest generation of persistent slabs.  The slab involved snow from the past week over the facets and faceted crusts that formed during our prolonged January dryspell.   Storm totals from the past week exceed 18" in the Northwest Mountains (1.8" SWE at Schofield Pass) and half that or less in the Southeast Mountains. We're showing a broader distribution of persistent slabs in the Northwest Mountains, where instabilities breaking on the 1/19 layer are likely to extend into wind sheltered and some windward aspects.   In the Southeast Mountains, with smaller storm totals and less slab formation, the new generation of persistent slabs will be mostly localized to leeward terrain.  Leeward terrain near and above treeline is also where you are most likely to find lurking instabilities on weak layers near the ground in both forecast zones.  That's where stiffer, thicker slabs remained intact following the dry spell and wind events of early January.  Below treeline, these larger, thicker slabs are isolated.  

Our initial impression is that avalanche activity and signs of instability from this storm weren't as widespread as expected.  With lighter winds and light snowfall in the forecast for today, we are starting to lower the avalanche danger to reflect an expected downturn in natural and human triggered avalanche activity.  The Southeast Mountains are the first to go to Moderate danger because they saw smaller storm totals.   An uptick in snowfall and wind tomorrow may reverse the trend on Tuesday.  

 

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