Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 2 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Persistent slab avalanches, which can release several feet deep and become very large in size, remain the primary avalanche problem. Trigger points, or areas where the snowpack thins to a below-average depth are the most likely areas to trigger these avalanches. This was just the case yesterday, with 2 notable avalanches being remotely triggered from wind-exposed ridgelines that had variable snow depths. This video is like eating some humble pie and is a great example of the potential avalanche size. There is a notably lower chance of triggering this avalanche problem in areas where the snowpack is consistently deep across the terrain. As the snow surface warms today, wet avalanche activity will increase, and in isolated areas, a wet avalanche could pull out a larger slab avalanche. 

Avalanche problems

  • Persistent Slabs

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

    In areas with a total snowpack height of over 2 meters, weak layers are continuing slowly gaining strength. In the NW Mountains, there has been a notable downturn in avalanche activity in March, compared to February. These two recent avalanches were triggered from areas with variable snow depths and highlight the potential size if you find the right trigger point (1 & 2). Since early February the weak layer that produced the most avalanches was a layer of buried surface hoar and small facets, several feet deep on the north half of the compass. There is also potential for avalanches to break on faceted crust layers on some higher, southerly aspects, or depth hoar layers near the ground. Persistent slab avalanches can still be triggered after multiple people have traveled across a slope, and will be more likely to be triggered from a trigger point where the snowpack thins to a below-average depth. Avalanches breaking into old weak layers are unlikely on low elevation, southerly aspects. Slope angles consistently less than 30 degrees away from runout zones are a reliable way to avoid the problem. 

    Remotely triggered avalanche. West, 10,400ft. The snow height here is 115cm. 

    Photo: Evan Ross

  • Loose Wet

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

    As snow surfaces warm, expect the potential for wet avalanche activity to increase. This avalanche problem will be most likely on slopes holding dry snow this morning, that becomes wet for the first time today. Steep slopes with cliffs and rock outcross will produce the most avalanche activity as those rocks absorb more heat and transfer that heat into the snow. In most cases, this avalanche activity will be small, easy to identify and avoidable. In isolated areas, wet avalanche activity could produce a larger slab avalanche. Keep an eye out for wet avalanche activity today and consider moving to colder aspects as steep and sunny slopes heat up through the day. 

    A small loose wet avalanche.

    Photo: Evan Ross

Avalanche Discussion

The thing that makes me the most nervous this weekend, is not all the recent persistent slab avalanches in our avalanche database, but the strong March sun coming out in force through the weekend. The snowpack is beginning its very first phase of a spring transition. We are not looking at water running through the snowpack like in late spring, but we are looking at the upper snowpack rapidly warming through the day, with some snow surfaces becoming wet. The snowpack doesn't like rapid changes. Whether it is this warm-up, or a warm-up later this spring, we are getting into the time of the year when surprising or unexpected avalanche results can occur. Wet avalanche activity this weekend, could pull out a stubborn persistent slab, and cornices may fall adding a very large load to the snowpack.

It has been a busy few days with persistent slab avalanche activity. Let's look at the trends. The vast majority of slab avalanche activity has occurred in the SE Mountains. That is because there are more areas in the SE Mountains where the total snowpack height is near or below 180cm. In those areas, buried persistent weak layers have not gained much, or any strength over the last month. Those weak layers are also closer to the snow surface and it is easier for the weight of a human to affect them. In the NW Mountains, we had a quiet week for avalanche activity up until yesterday. Persistent slab avalanches are less likely in the NW Mountains because the total snowpack height is more commonly over 200cm in depth. Persistent weak layers in areas with a deep snowpack have gained strength over the last month, and they are also buried deeper where it is harder for the weight of a human to affect them. The 2 persistent slab avalanches that were triggered in the NW Mountains yesterday, were both triggered from areas where the snowpack was below average in depth, due to previous wind erosion earlier this winter. Those avalanches then propagated out into areas with a deeper snowpack. You can measure total snowpack depth using your avalanche probe which has measurements marked in centimeters. For reference 30 centimeters = 1 foot. 

This will be an absolutely lovely weekend to get out in the mountains. If you want to ride in avalanche terrain, consider making a plan to ride in areas with a consistently deep snowpack while keeping an eye out for changing conditions throughout the day as snow surfaces warm. Then check back into the avalanche forecast before Sunday to see how the snowpack is holding up to this spring-like weather. 

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