Bulletin d’avalanche

Northwest Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The sun is shining, obvious signs of instability are decreasing, but it is important to remember there is still a monster hiding under the snow surface. Yes, monsters are scary just like our current Persistent Slab Avalanche Problem. A triggered avalanche would be large enough to burry and/or kill you.  The simple way to reduce your exposure to an avalanche is skiing/riding on the southern half of the compass, or where this avalanche problem is highlighted, to continue riding low angled slopes. Careful snowpack and terrain evaluation are necessary to cautiously step beyond those boundaries. 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2

    Dangerous avalanche conditions remain on previously wind-loaded terrain at near and above treeline elevations. These slopes will primarily face northeast and east. Human triggering a potentially deadly avalanche remains likely in these areas. In other areas, heightened avalanche conditions continue to exist, primarily on terrain with slope angles near or above 35 degrees. 

    Obvious signs of instability such as collapsing and shooting cracks have decreased in recent days. Without these obvious warning signs, it is important to not become complacent or overconfident. The nature of Persistent Slab Avalanches is that they can be triggered days to weeks after the last storm. They can also be triggered from below a slope, and will often propagate widely across and beyond terrain features.

     In the Northwest Mountains, these slabs are 1 to 2 feet thick in sheltered locations, and significantly deeper on drifted terrain features. 

    12/23 - A remotely-triggered avalanche below treeline at the head of the Slate River Valley.

Avalanche Discussion

Our snowpack is built upon a layer of facets that was buried 12/10. This particular weak layer has been quoted as "one of the worst" since 2012. When these facets were buried, they were widespread on west, to north, to east aspects, and some upper elevation southeasterly facing slopes. This weak layer has seen little improvement over the last couple of weeks. Just scroll through the observations page and you will see lots of natural and human triggered avalanches. What has changed in the last several days, is the distribution of snow and slabs over this weak layer. The redistribution of this snow came from an extreme wind event on 12/23, with westerly winds, followed by continued strong winds from the northwest to north. These winds removed snow from some slopes and created hard slabs on others.

West to northwest facing slopes saw the most snow get stripped away. These slopes have now been removed from the persistent slab avalanche distribution rose, as an avalanche on these aspects will be less likely to be triggered than on other aspects. Northeasterly and easterly facing slopes at mid and upper elevations saw the most loading and building of the slab. Many of those slabs are now very hard, and it has become more difficult for the weight of a human to affect the weak layer below. However human triggering one of those hard slabs would make for a nasty avalanche. Near treeline elevations may now be the most suspect for human triggering. Here the slabs will be larger than down at lower elevations, but the slabs will not be as hard as upper elevations. 

The avalanche danger at below treeline elevations was dropped to MODERATE. Here the most suspect terrain for triggering an avalanche has become slightly more specific. Such as terrain with slope angles near or above 35 degrees. Human triggering an avalanche remains possible, and the resulting avalanche could still be large and deadly. 

Régions couvertes