Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

You may be able to trigger avalanches in both sheltered and wind-affected terrain. In areas protected from the wind, 1.5-2 foot thick avalanches are possible on shady slopes. In more exposed locations, you may be able to trigger hard or soft drifts or slabs that formed over the past several days. Even small slides can have big consequences on slopes with cliffs, trees, and terrain traps.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–2

    In the past two weeks, skiers and riders triggered several avalanches involving a layer of surface hoar buried 1.5-2 feet deep. A skier triggered a slide on this layer Sunday in the Salmon River drainage (view report). The surface hoar "problem" remains capable of producing avalanches on some slopes steeper than about 35 degrees. 

    Buried surface hoar is challenging to deal with. Its patchy distribution means you may find it on one slope but not the next, and it can be hard to identify when searching for it in a snowpit (example). It's often best preserved and more sensitive in small clearings and open, wind-protected terrain on shadier aspects. 

    You can reduce your risk by avoiding slopes facing NW-N-NE that are steeper than about 35 degrees. Consider the consequences of going for a ride. Even small slides can have bad outcomes if they lead to trees, cliffs, or a creek bed. 

    ADDITIONAL DISCUSSION: Last weekend's snow and northerly wind formed thin, soft slabs in exposed terrain (Cape Horn Mtn). You could trigger a similar slide today. Look for wind slabs near ridgelines, on the sides of gullies and chutes, and near prominent terrain features. Cracks shooting out from your skis or sled are an obvious sign of instability (example).

     

    (1/23/2023) Avalanche apparently triggered by a skier on Banner Summit. Slab depth and terrain characteristics are consistent with early January surface hoar layer. 7250', NNW. The date of this avalanche is uncertain, but likely occurred since Jan 18th. Photo taken Jan 23rd.

Avalanche Discussion

Here's a quick top-down overview of the snowpack and associated avalanche concerns:

Near the Surface

  • Loose Snow Avalanches: Today's warm temperatures and direct sun may peel soft snow from wind-sheltered, rocky, extreme terrain. Although mostly small, some of these slides will collect enough snow to sweep you off your feet or bury you in a depression. Keep this problem in mind if you're traveling on or beneath large, rocky slopes this afternoon. 

Upper Snowpack

  • Wind Slabs: A few generations of wind slabs formed in the past week. The most recently formed slabs are softer and may be more reactive to your weight. However, the large, recent slide in the Soldier Mtns probably involved rock-hard snow that drifted onto the slope last week; triggering beasts like that is not entirely out of the question. Triggered wind slabs can be effective triggers for deeper weak layers in the snowpack.
  • The persistent weak layer (facets or surface hoar) buried in early January lies beneath a 1.5-2 foot thick slab; impacting it remains a very real possibility. This layer is ugliest on wind-protected, shaded slopes (those on the northern half of the compass) where surface hoar formed. However, a pattern of unstable snowpack test scores on sunnier slopes—where facets and surface hoar lie above a crust—is worth noting. Triggering an avalanche on this weak layer is possible in both sheltered and wind-affected terrain.

Middle and Lower Snowpack

  • Snow depths in most of this zone exceed 6 feet. Weak layers that were buried in November and December lie beneath very dense, heavy slabs of snow. Impacting these weak layers is unlikely but not impossible.

The consequences of triggering avalanches can vary significantly. Triggering a small slide in terrain free of rocks, trees, and terrain traps is much less dangerous than triggering a slide in extreme, rocky, treed terrain with a terrain trap at the bottom. Think about the consequences of being caught in a slide before committing to skiing or riding in sizeable avalanche paths. 

Régions couvertes