Boletín de aludes

Banner Summit

Sawtooth Avalanche Center
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Peligro de aludes

Sat
Alta montaña
1 · Débil
Límite del bosque
1 · Débil
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Mostly stable avalanche conditions exist, and large avalanches are unlikely. While your odds are low, triggering a 1.5-2 foot thick avalanche cannot be ruled out on some sheltered, shady slopes. In wind-exposed terrain, be on the lookout for small, thin pockets of drifted snow. Even small slides can have big consequences on slopes with cliffs, trees, and terrain traps.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    1.5–2

    Since mid-January, skiers and riders have triggered several avalanches involving a layer of surface hoar buried 1.5-2 feet deep. A skier triggered a slide on this layer last weekend in near Galena Pass (view report). The surface hoar "problem" is stabilizing, but it remains capable of producing avalanches on isolated 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 effectively 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 encounter similar small, sensitive drifts 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 what's happening in the snowpack:

Upper Snowpack

  • The persistent weak layer (facets or surface hoar) buried in early January lies beneath a 1.5-2 foot thick slab. Its shallow depth means impacting it remains a very real possibility. I found this layer in all of the pits I dug Wednesday near Cape Horn Summit (observation). While present, snowpack tests indicated that this layer is stabilizing. Ben found similar results last Saturday in his pits near Copper Mtn. While unlikely, I'm not ready to ignore the chance of triggering a slide on wind-protected, shaded slopes where this layer is at its worst.
  • A few generations of wind slabs formed in the past week. The most recently formed slabs are small and softer but may be more reactive to your weight. Warm mountain-top temperatures have helped this problem heal, but I'd keep it on your radar if you plan to ski or ride wind-exposed 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. 

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