Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Persistent slabs are becoming increasingly isolated and unreactive during our quiet weather pattern in the Northwest Mountains.  As a safeguard against a rare but dangerously large avalanche, choose routes that minimize exposure to shallow and rocky areas. Instead, target objectives with a deep (more than 150 cm) and uniform snowpack.  Stay alert for fresh wind slabs forming above high-consequence terrain in the alpine.  

Avalanche problems

  • Persistent Slabs

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

    On most slopes in the Northwest Mountains, faceted weak layers are buried deeply and becoming unreactive to triggers.  Some slopes have unusually shallow or variable snow depths where riders may be able to trigger a hard slab several feet thick or more.  Be cautious of windward terrain features with variable depths, rock bands, and slopes that previously avalanched in early December where you are most likely to find a thin trigger point.   The safest riding is where the snowpack is uniform and consistently deeper than about 5 feet (150 cm).  

     

    This large avalanche failed on Ruby Peak around January 18th.  This exemplifies the type of terrain with lingering concerns.  It's a windward slope with below average snow depths and numerous rocky areas.  

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Northwest winds are increasing to transportable speeds today at higher elevations.  Expect to encounter thin wind drifts forming below ridges and cross loaded features in the alpine.  Although they should be small and easy to skirt around, fresh drifts could be an issue if you get knocked over in consequential terrain such as above cliffs or gullies.  

    Example of a small wind slab in a crossloaded gulley on Gothic.  

Avalanche Discussion

With an increase in wind speeds overnight and a couple of inches of fresh snow available for transport, we've relisted wind slabs as a developing problem.  Fresh wind slabs should be small and easy to avoid, but stay alert in high-consequence terrain.  

The sensitivity of persistent slabs continues to gradually decline under our relatively quiet weather pattern.  Explosive testing on windward aspects yesterday at Irwin did not produce results.  In the Northwest Mountains, the snowpack is deeper and stronger, and the threat of triggering a persistent slab is trending away.  We still have some isolated concerns for atypically shallow slopes where wind erosion or previous avalanche activity make it easier for riders to impact weak layers.  There's a significant change in snow depths and structures as you travel to the shallowest parts of the Southeast Mountains.  Yesterday, targeted stability tests near Red Mountain produced unstable results on both of our prominent weak layers in the lower snowpack.  Not all of the Southeast Mountains have such a poor structure; some areas have a deeper and more trustworthy pack as well.  This map of modeled snow depths around our forecast area paints a generalized picture of the deeper and more trustworthy areas vs. the have-nots.  The goldilocks snow depth for finding the most troublesome structure seems to be around 3 to 4 feet (90 to 120 cm).   

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