Boletín de aludes

Southeast Mountains

Crested Butte Avalanche Center
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Peligro de aludes

Sat
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

Natural and human-triggered avalanches yesterday offer strong evidence that you can trigger a dangerous avalanche on drifted terrain today.  Sensitive drifts can even be found below treeline in atypical locations in addition to classical leeward features at upper elevations.    Slopes less than 30 degrees that are not directly below recently drifted terrain offer safer options.

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 3-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.  Thin spots are most common in wind-affected terrain or near rock bands or vegetation.  

    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
    Likely
    Tamaño
    1–2

    Extreme westerly winds have blown the new snow and old snow surfaces to leeward terrain features.  Very strong winds can produce atypical loading patterns.  Look for loading in traditional areas below ridgetops, underneath cornices, and behind terrain breaks, but don't be surprised to find fresh drifts below treeline or lower in start zones than you are accustomed to.  An avalanche in recent drifting may trigger an avalanche deeper in the snowpack where it overlaps with the Persistent Slab problem.

    A remotely-triggered avalanche from an open below treeline slope on Thursday, 12/22.

Avalanche Discussion

Strong to extreme winds on Wednesday night and Thursday transported snow to leeward features.  The drifting snow overloaded the snowpack and caused natural avalanches at all elevations.  At least one natural avalanche on Mount Emmons appeared to break near the ground while others appeared to break in the upper snowpack.  There was certainly not a widespread avalanche cycle but enough observed natural avalanche activity to strongly support a CONSIDERABLE danger rating.  Terrain with signs of recent drifting remains highly suspect today regardless of elevation.  Upper-elevation drifted slopes are more dangerous because avalanches there are likely to be much larger.

In addition to the natural avalanches, two separate remotely-triggered avalanches occurred.  One was below treeline on open terrain near Snodgrass.  This slope has an obvious open fetch where the wind was able to gather snow and deposit a stiff slab.  Forecasters walked above this slope after identifying recent drifting and easily released that stiff slab while approaching the top of the slope.  The other remote trigger came from southeasterly terrain above Irwin.  Observers were surprised by "the fracture's impressive ability to propagate around interrupting terrain features".  This avalanche serves as a good reminder that you can still trigger avalanches from a distance and avalanches may behave in surprising or erratic ways.

Avalanche conditions remain dangerous and tricky.  Moving through avalanche terrain requires cautious travel and conservative decision-making.  The simplest solution, as always, is selecting slopes around 30 degrees or less without overhead avalanche hazard.

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