Boletín de aludes

Northwest Mountains

Crested Butte Avalanche Center
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Peligro de aludes

Sun
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Continued recent destructive avalanches (Example A, Example B) in the alpine serve as a stern warning for the type of avalanche you can trigger today.  Avalanches breaking near the ground are slowly becoming harder to trigger and will give few obvious warning signs.  Make no mistake, the snowpack structure is untrustworthy and requires a conservative mindset.  Wind-protected slopes that face south and southwest offer the safest steep riding options, and deep, uniform snowpacks at lower elevations have a lower risk of triggering a deadly avalanche. 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    Storms this month have built thick and hard persistent slabs over a widespread weak layer of facets and faceted crusts. These slabs are generally 2 to 4-feet thick. The vast majority of avalanche activity this month has occurred on west to north to southeast aspects, with only a few avalanches from alpine south to southwest facing alpine terrain. Persistent slabs are notorious for erratic feedback and unusual behavior, such as remote triggering and wide propagation. To reliably avoid the problem, choose routes that keep you off and out from under terrain steeper than about 30 degrees that hold old, weak snow near the ground. In steeper terrain, you can reduce your chance of triggering an avalanche by avoiding trigger points where the snowpack is thinner than average.  

    This persistent slab avalanche wrapped from shady to sunny aspects and broke on weak layers near the ground. This a good example of the potential size and widely propagating behavior of our current persistent slab problem. 

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Several days of northwesterly winds built stiff wind slabs on the lee sides of ridgelines and cross-loaded terrain features. This avalanche problem will dictate how you manage some southerly-facing terrain, where persistent slabs are less common. Consider routes that avoid recent drifts and lens-shaped snow deposits.  Look for softer, wind-sheltered snow to avoid the problem.  

Avalanche Discussion

The avalanche danger is slowly trending down through the weekend with natural activity expected to diminish and human triggering gradually becoming more stubborn each day.  The potential avalanche size and our travel advice are dictating the Considerable danger rating near and above treeline.  Numerous avalanches up to D3 in size ran over the past week, some within the last 48 hours.  A few of these ran almost full track to the valley bottom in the Northwest Mountains.  This video from yesterday describes how you can trigger a very large avalanche from the alpine.  Not necessarily from the fattest part of the start zone, but when you cross a thin spot near a rock band, wind-eroded feature, or other inconspicuous thin areas.  Last weekend's remotely triggered avalanche in Red Lady Bowl is a great example of how avalanches can be triggered from a distance.  With such variable snow depths in the alpine and a clear pattern of continued dangerous avalanche activity, conservative terrain selection is advised at higher elevations. 

There has been significantly less avalanche activity below treeline in the past week, where the danger is lower.  There are a number of variables contributing to this.  The natural activity over the last few days has been driven by wind loading, rather than significant snowfall.  In addition to undergoing less stress, below treeline slopes tend to have more uniform slabs with fewer thin spots for triggering, particularly in the snowfall-favored Northwest Mountains.  We saw more extensive avalanche activity earlier in the month below treeline, which may have helped flush or disturb the weak layer in some cases, and in some cases in the shallower zones, the weak layer is discontinuous along the ground helping to reduce avalanches.  With that being said, there is still serious potential to trigger a dangerous avalanche below treeline today.  If your assessments in this type of terrain suggest it's appropriate to step out, consider consequences such as slope size and terrain traps.  Slabs tend to be a bit thinner but more reactive closer to town, and thicker but more stubborn in more snow-favored areas away from the donut hole.   

Events: CBAC is teaming up with Irwin Guides to offer free beacon training today at Slate River Trailhead. Sessions will run at 10:00, 11:00 and 12:00. 

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