Boletín de aludes

Northwest Mountains

Crested Butte Avalanche Center
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Peligro de aludes

Sat
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

We are nearing the end of the recent extreme wind event. These NW winds were so strong, that much of the snow was blown over to Kansas and Oklahoma. Where that blowing snow did land back on a slope, a fresh hard slab has now formed. Your primary avalanche problem is where you find these hard slabs over old weak snow. These slabs may have formed in unusual locations, and will otherwise be most likely to encounter on the lee sides of ridgelines and cross-loaded terrain features. 

Problemas de aludes

  • Persistent Slabs

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

    On or near steep terrain, you can trigger persistent slabs 2 to 4 feet thick that fail on weak snow near the ground.  Persistent slabs often surprise even the most experienced travelers: They give irregular feedback, they can propagate unusually wide distances, and they can be remotely triggered from below or adjacent to the slope.  To avoid this problem,  choose routes that stay off of, and out from underneath, steep terrain holding dense slabs over sugary weak layers.  Poor structure is most common on the slopes highlighted by the distribution rose above, on west to north to east and some southeast slopes.   Shooting cracks and collapses are clear warning signs to stay on slope angles less than about 35 degrees, although their absence isn't a guarantee of safety.   In the Northwest Mountains, slabs are generally thicker and denser: you are most likely to trigger them from shallow points on the slope such as rock bands, pungie trees, or where slabs taper in thickness from wind effects.  

    12/31: A large, remotely triggered persistent slab in Redwell Basin

Avalanche Discussion

The current extreme wind event started up late Wednesday. The peak wind gust we saw in our area was recorded Wednesday night and hit near 90mph at 12,000ft on Cinnamon Mountain. Since then, strong winds have continued to hammer at all elevations. Only 2 fresh avalanches have been recorded so far, and visibility was a bit limited yesterday. One avalanche was observed on a cross-loaded near treeline slope that faced ESE, and the other was right here in Crested Butte on a small low elevation wind-loaded slope. Neither of these avalanches were particularly big. However unusual conditions, such as this wind event, can typically surprise us with unusual results. You do not want to trigger a hard slab avalanche breaking several feet thick at mid to upper elevations. That would be a nasty avalanche. Given the hard nature of these slabs, we can expect them to be stubborn to trigger and give basically no warning to their potential instability in the form of obvious red flags such as shooting cracks or collapses. 

These winds have redistributed and drifted snow even down low in the valleys. Previous to this wind storm we were transitioning from a slab avalanche problem, back to a facet sluffing avalanche problem. Now you could encounter fresh hard slabs, typically on cross-loaded terrain, at low elevations. The Avalanche Danger in the SE Mountains was bumped back up to Moderate yesterday for this reason. That danger remains the same today. 

SE near treeline was added into the most likely areas under the Persistent Slab Avalanche Rose this morning, due to recent wind-loading onto those slopes. Once we get more eyes on the terrain, W and NW may soon be on the chopping block from that avalanche rose as many of those slopes are probably blown back to the ground. W and NW were already removed from the SE Mountains, but currently remain on the problem rose for the NW Mountains. 

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