Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 6 months ago.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

Highlights

The avalanche danger will rise throughout the day as new snow continues to accumulate. The older persistent slab problem has a lower likelihood of triggering but carries high consequences if it releases.  So keep those potential consequences in mind when you're considering your terrain choices today, or head to southerly facing terrain to avoid the problem. The accumulating new snow will create dry loose avalanche conditions in steep terrain, or shallow soft slabs can develop, primarily where the snow is accumulating over a faceted snow surface on the northern half of the compass. Terrain selection is the key to enjoying some much-needed powder. Southerly-facing terrain avoids the biggest avalanche problem, and lower-angle slopes or smaller terrain features are other areas to consider for limiting your avalanche exposure. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Slabs over buried weak layers 1.5 to 3 feet thick are typically stubborn to triggers, as the hard slabs are often insulating the buried weak layers from the weight of a human. Triggering would most likely occur from areas where slabs are thinner. Obvious signs of instability are rare to non-existent.  Persistent weak layers are buried in the middle and bottom of the snowpack. Avalanches can be remotely triggered from steep or adjacent flat terrain (see several videos illustrating this) and propagate widely through the terrain. Some higher-elevation southerly terrain also harbors problematic structures. The most reliable strategy for managing this problem is to choose conservative slope angles or travel on mid- to low-elevation southerly aspects.  On problematic aspects, avoid traveling in or near steep terrain where slabs are thin or variable in thickness, such as convexities, rocky areas, or wind-affected terrain.   

     

    A large persistent slab avalanche that failed around 2/25 near Purple Ridge. 

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Dry loose avalanches will initially be reactive in steep terrain and run fast on the old firm snow. As new snow continues to accumulate today or during periods of higher precipitation, new soft slabs may form. These slabs can fail on old hard snow surfaces, but they would be the most reactive on the faceted snow surfaces that exist on northerly-facing terrain. Keep an eye out for changing conditions through the day. 

Avalanche Discussion

The primary difference between the forecast areas today is the potential sensitivity of the old persistent slab avalanche problem. The slabs that were created in February have become very hard across the forecast area. That makes buried weak layers harder to affect. Where those slabs are thinner than average is where triggering is the most likely. Slabs are more commonly thinner in the SE Mountain forecast area, and Zach's recent field day in upper Cement Creek helped illustrate this. Where weak layers are buried in a ~120cm+ snowpack, we have made a few observations of those weak layers gaining some strength. The problem is that total snowpack depth can vary greatly from slope to slope, or from one part of a slope to another, due to both trigger points and old avalanche activity creating a localized snowpack that is below average in depth. New snow accumulations in areas like the Friends Hut and Upper Cement Creek could do similarly well to typically snow-favored locations like Schofield Pass, thanks to some northerly flow. 

Two observations yesterday made note of the weak snow surface on northerly facing slopes heading into this storm. (1,2). This will be the primary weak layer if we see new soft slabs form in the new snow. Upper elevations could see some interesting conditions develop as the new snow will be sliding off some terrain features that have a widespread layer of exposed ice, and other areas that have very thin ice layers separated by facets. 

Regions covered