Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Previously wind-loaded terrain remains the most suspect for triggering a slab avalanche today. This avalanche problem can most commonly be found below ridgelines and on cross-loaded terrain features. The potential avalanche size and sensitivity to triggering will be greatest at upper elevations. In wind-sheltered terrain, we can't completely rule out soft slab avalanches releasing on persistent weak layers in the upper snowpack. The most suspect wind-sheltered terrain would be steep easterly and northeasterly facing slopes, where recent storm accumulations exceed 12" of new snow. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    At 12,000ft, westerly winds averaged 15 to 25mph yesterday, and have since calmed down overnight. These previous winds have formed fresh slabs below ridgelines and on cross-loaded terrain features. These slabs could release in the most recent snow, or 1 to 3 feet deep on recently buried persistent weak layers. You may be able to identify this wind-loaded terrain by a smooth rounded pillowy appearance and stiffer feeling snow textures. 

    Example from earlier this winter of active transport and Wind Slab formation. Terrain like this beneath a ridgetop and cornice are highly suspect places to trigger a Wind Slab today.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    Hard slabs that break 2 to 6 feet deep on weak layers near the ground remain a low likelihood concern.  The problem has become increasingly stubborn and isolated, and it has been several weeks since we have observed a persistent slab avalanche.  There is lingering uncertainty that skiers or riders can trigger a large avalanche from the margins of the slab where it thins out,  especially at higher elevations on northerly and easterly aspects.   Cornice falls can also trigger large avalanches.  You can reduce your risk by traveling where the snowpack is deeper and more uniform.  Regroup in safe zones that are clear of unusually wide and long-running avalanches.  

    An example of a thick, hard persistent slab that released naturally in mid-February.

Avalanche Discussion

Since last week, the most notable change in conditions has been fresh snow and wind. The term "Doughnut hole" was used to describe the wide variation in recent snow accumulations for our forecast area. Since last Friday, snow totals range from 6 to 20+ inches. Areas further west like Irwin accumulated near 20+ inches and places in the far east near the top of Cement and Brush creeks squeezed out totals closer to 12". While areas near Crested Butte only received around 6 inches.

Forecasters have been tracking persistent weak layers in the upper snowpack that were recently buried under this fresh snow. We have observed a couple of small slabs that may have released on these layers of concern. However so far there doesn't appear to be a new widespread persistent slab issue. The avalanche danger below treeline has been held at MODERATE due to uncertainty around just how isolated a new persistent slab avalanche problem is. In the big picture, there doesn't appear to be enough new snow to have created a new avalanche problem. The areas that accumulated 12+ inches of new snow would be the most suspect. 

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