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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Highlights

Large to very-large slab avalanches breaking deeply in the snowpack have become unlikely in the big picture. Heightened avalanche conditions remain on steep slopes with a below-average snowpack depth and for any lingering old wind slabs that may have formed at upper elevations during yesterday's northerly winds. Consider avoiding steep rocky terrain, unsupported slopes with cliff bands below, and places with highly variable depth from wind effect. Instead, chose terrain with deep and uniform snowpack coverage, if you are stepping out to more aggressive terrain.

Avalanche problems

  • Persistent Slabs

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

    Slabs ranging from 5 to 8+ feet thick are resting over faceted weak layers in the lower snowpack around much of the compass. These weak layers have generally adjusted to their current load and are trending towards unreactive. The most suspect areas to release this avalanche problem would be from trigger points or areas where the snowpack thins to a below-average depth. Such as near rock bands, on some slopes that previously avalanched and have refilled, or where winds have formed variable snow depths. 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 and not connected to steeper terrain above.  

     

     

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

Avalanche Discussion

In the Northwest Mountain Forecast Area, this is a great day to be stepping out in your terrain choices. If you would like to step out in those terrain choices cautiously, do so in those areas with a deep and uniform snowpack. A 230cm+ snowpack is starting to get more comfortable into a depth that could be characterized as deep. The forecast team has been having discussions about areas that they are the most concerned for triggering the low probability but high consequence persistent slab avalanche problem. Those areas are generally slopes that look to hold a thinner snowpack relative to average. Think of a NW-facing slope that has spent much of the winter blown off and holding a shallow snowpack with well-developed weak layers. Then last week we had a couple of big storms roll through depositing 2 to 4 feet of snow on those slopes with little wind during that time. Those slopes will still have a below-average snowpack depth, but they may have recently doubled in height and would likely remain the most reactive on the avalanche front. That terrain doesn't have to be a windward aspect, it could also be a steep east face for example that hasn't yet developed a deep snowpack, perhaps due to previous avalanche activity. The big picture sensitivity of the primary avalanche problem fits level 1 avalanche danger, however, we are still employing level 2 travel advice and are not in a full open season mindset, until those concerning areas have had more time to adjust to last week's loading event. 

In the Southeast Mountain Forecast Area, the persistent slab avalanche problem is more concerning and it is more common to encounter an area where you can trigger the persistent slab avalanche problem. The most concerning areas will likely line up where the total snowpack depth is in the 100 to 150cm range. In those areas, there is a better chance to encounter a relatively thin slab where your weight could more easily affect a buried weak layer near the bottom of the snowpack. The recent northerly wind event will have formed a few small wind slabs, primarily at above treeline elevations. These slabs will have become stubborn to human triggering, but they will be worth keeping an eye out for if you are riding in bigger or extreme terrain.

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