Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

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

Points saillants

Triggering a 1-3 foot thick avalanche is likely. Avalanches are most likely in areas exposed to the wind. You may trigger avalanches remotely — from flat terrain below, above, and to the sides of steep slopes.

Problèmes avalancheux

  • Persistent Slabs

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

    Freshly formed slabs rest on a mix of weak snow surfaces, including facets, surface hoar, and crust + facet combinations on slopes that face the sun. The widespread nature of this weak layer means avalanches may be easy to trigger on many aspects and elevations. 

    Conditions are most dangerous where wind-blown snow forms thick, stiff slabs at the snow's surface. Avalanches are also possible on steep slopes at middle and low elevations that are more sheltered from the wind.  

    Persistent Slabs can release in surprising ways, break wider than expected, and release hundreds of feet away from where they are triggered. Remotely triggering an avalanche from flat terrain in the valley bottom is a real possibility. Keep a close eye on your partner and the terrain that's above you.

    Additional Discussion: While less likely, avalanches may fail in weak snow near the ground. The resulting avalanche would be large enough to destroy a house. This scenario is most likely on shaded NW-N-NE facing slopes above about 8,000'. 

    (12/1/2024) This is an example of the wide, large avalanches you could trigger. This slide occurred in the N. Boulders after our last significant storm. 

    Photo: Sawtooth Avalanche Center

Avalanche Discussion

36-hr storm totals for the Banner Summit Zone are 8-18" (0.7-1.4" SWE). Yesterday's snow fell with light to moderate S and SE wind. A cold frontal passage last night brought a temporary uptick in wind speed and a shift to the SW and W. 

Today, caution is the name of the game. We built slabs on a shaky foundation, and the safe bet is to assume they won't play nicely with the myriad of weak layers they rest on (see examples below.) 

Seeking out softer snow and lower-angle terrain is a good approach, but don't overlook the possibility of triggering a slide from the base of a slope. Build a wide safety margin today as buried weak layers adjust to the load.

Régions couvertes