Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
Voir sur la carte

Danger d’avalanche

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

Points saillants

We're facing a classic low probability-high consequence situation—avalanches are becoming more difficult to trigger, but they will be large and destructive. You are most likely to trigger a wide, 3 foot thick, dense slab avalanche in steep, rocky terrain that is affected by the wind. Avalanches may be triggered remotely—from below, above, and to the sides of steep slopes. 

Problèmes avalancheux

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    The same layer of weak faceted snow that exists in our other zones also exists in the Banner Summit Area. The big difference here is that the weak layer is buried beneath a dense, 3-foot thick slab of snow. The dense slab is "protecting" the weak layer, making it more difficult for skiers and riders to trigger slides. However, if you are unlucky enough to trigger one, the resulting avalanche will probably be large enough to snap trees and leave piles of debris many, many feet deep. Yuck. 

    Ben does a nice job explaining the situation in this video. He also observed evidence of very large, deep slab avalanches that failed during the storm last week. The photo at right/below shows one of the slides he saw. 

    Deep slabs behave unpredictably, often releasing after many riders have already traveled on a slope. Tracks on a slope do not guarantee it is stable. You are most likely to trigger one of these monsters in steep, rocky terrain at upper elevations. In these areas, thin spots in the snowpack created by wind scouring and/or uneven ground cover bring the weak layer closer to the surface.

    The sad truth: the best—and often only—way to manage a deep persistent slab problem is by sticking to lower-angled terrain and steering clear of slopes with runout zones that have trees, rocks, or terrain traps. Given the possibility of remote-triggering slides, avoiding playing directly beneath rocky avalanche starting zones also reduces the chances of getting in trouble. 

    (1/18/2021) This very large avalanche occurred in our Banner Summit Zone, likely during last week's storm. Based on the depth and appearance of the crown it probably failed on facets buried deep in the snowpack.

Régions couvertes