Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

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

Points saillants

Avalanches are most likely where the wind has formed drifts or stiffened the snow surface. Avalanches are less likely in areas sheltered from the wind. You could trigger slides 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
    Possible
    Taille
    2–3

    You could trigger 1.5-4 foot thick slabs, especially where wind formed drifts or stiffened the snow surface. Triggering an avalanche is less likely—but not out of the question—on steep slopes that are completely sheltered from the wind. The slabs rest above a variety of weak layers (facets, surface hoar, and crusts + facet combinations). The widespread nature of these weak layers means avalanches are possible on many aspects. 

    Snowpack cracking and collapsing or whumpfing are clear signs of unstable conditions. However, a lack of these obvious warning signs doesn't mean you're in the clear. The first sign of instability you observe may be the large avalanche you trigger. 

    Avoiding steep, wind-loaded slopes can significantly reduce your chances of triggering an avalanche. Persistent Slabs can release in surprising ways, break wider than expected, and release above or hundreds of feet away from where they are triggered. Manage your group by riding or crossing steep slopes one at a time, and consider avoiding areas where terrain features like gullies, cliffs, or dense trees could increase the consequences of a slide.Additional Discussion: You may be able to trigger wind slab avalanches that formed near ridgelines and in cross-loaded areas on the sides of gullies. The size and chance of triggering these slides increase significantly as you climb into windier, alpine terrain at upper elevations. These avalanches could step down to the buried weak layers described above. Watch for snow pillows, dunes, and ripples, and feel for stiff snow under your feet or sled. These are signs the wind has been at work transporting snow.

    (12/31/2024) Large natural avalanche in the Banner Summit area. This slide released during the post-Christmas storms. Photo: Jeremy Lato

Avalanche Discussion

The snowpack is gradually adjusting to the weight of recent storms. This process takes time and is slowed by ongoing snowfall and wind-loading.

Here is a recap since Sunday:

  • So far, we've recorded ~100 avalanches focused around preferentially wind-loaded NE and E aspects between 9,000-10,000' (view rose).
  • Twelve human-triggered avalanches were reported (view rose). Three of these were triggered Tuesday by skiers near Titus Lake.
  • Nearly all of the 50+ recent observations we've received report obvious signs of instability, such as avalanches, cracking, or collapsing. 

In the Banner Summit zone, weak layers are buried deeply in many areas, making avalanches more difficult to trigger. While there have been fewer reports of persistent slab avalanches here, that shouldn't be interpreted as a sign of stability.

It's snowed over a foot in most of this zone since New Year's Day. Observers from Banner Summit and across the forecast area have reported actively drifting snow. Look for fresh wind slabs near ridge tops, steep cliff faces, and chutes. While commonly small, these slides could still carry you into dangerous terrain or trigger larger, more hazardous, Persistent Slab avalanches. 

We're enjoying the great riding and skiing but remain cautious around or below avalanche terrain. Keep a close eye on your partner and the terrain above you.

Régions couvertes