Bulletin d’avalanche

Northwest Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

Sat
Alpin
2 · Modéré
Limite forestière
2 · Modéré
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

It has been two days since leeward terrain features received significant wind-loading.  The most concerning slopes will be at upper elevations that were previously drifted on Tuesday and Wednesday.  Lower elevation terrain without recent drifting is less concerning, but slabs and weak layers are common on the east half of the compass.  Choosing terrain with slope angles less than 35 degrees that are not connected to steeper terrain will help to reduce your chances of triggering an avalanche. 

Problèmes avalancheux

  • Persistent Slabs

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

    There are two flavors of persistent slabs that you can trigger today.  The problems are most dangerous on windloaded slopes where slabs are thicker. The youngest generation of persistent slabs is more widespread, on steep slopes where recent and windblown snow formed soft slabs over weak facets and faceted crusts in the upper snowpack.   The older generation involves stubborn hard slabs that could fail on weak layers near the ground - a more dangerous but more isolated problem.  Persistent slabs can be remotely triggered from below a steep slope or propagate widely across the terrain.  Shooting cracks and collapses are clear warning signs of this problem; however, persistent slabs are notorious for giving unreliable feedback.  For example, there were numerous tracks on the slope before a skier was nearly caught in the large avalanche on Schuylkill Ridge.  Give yourself a wide margin for error when assessing and managing persistent slabs.  

Avalanche Discussion

The avalanche hazard has slowly trended downward around Crested Butte.  Sheltered terrain is now about 5 days out from the last round of loading, and upper elevation leeward slopes are just two days out from the last wind-loading period.  Slabs and weak layers abound for elevations and aspects highlighted on the distribution rose for the Persistent Slab problem.  Recent observations from below treeline areas that face the east half of the compass suggest that triggering an avalanche remains possible.  Take a look at this ob from near Coneys and this one from Cement Creek to see snowpit test results that suggest the newer form of Persistent Slab, in the upper snowpack, is still a potential problem.  A simple solution to managing this problem below treeline is to pick terrain with slope angles less than about 35 degrees.  You can further reduce your risk by picking slopes that are free from terrain traps like gullies, rocks, or trees.

Drifted terrain at upper elevations offer a bit more uncertainty.  Slopes that face north through east through southeast have only gone 2 days without loading.  Natural avalanche activity was also observed on Wednesday due to the wind-loading.  A few of these natural avalanches failed deep in the snowpack in the Southeast Mountains near White Mountain and Twin Lakes.  One thing you can be confident of is the large and dangerous size of a triggered avalanche on a drifted slopes.  Venturing into recently drifted slopes near or above treeline currently offers the greatest avalanche risk due to the expected size and uncertainty about their sensitivity to human triggers.

An incoming storm will impact the Crested Butte area on Friday evening through the middle of Saturday which will favor the Northwest Mountains.  Expect a steadily increasing avalanche hazard on Saturday if the weather forecast verifies.

Régions couvertes