Boletín de aludes

Banner Summit

Sawtooth Avalanche Center
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Peligro de aludes

Tue
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 3 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Dangerous avalanche conditions exist. Triggering 1-3 foot thick avalanches is likely today.  Avalanches will be easier to trigger in terrain affected by the wind, but are possible in sheltered terrain as well. Avalanches can be triggered from long distances above, below, and to the sides of steeper slopes. 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1.5–2.5

    What is it? Layers of weak snow in the upper snowpack can produce large, wide, 2-3' thick slab avalanches. Last week Ben spotted a large avalanche on Copper Mountain. It broke about 2 feet deep on a layer of weak facets. The slide appeared to have been remotely triggered by a skier on a low-angle ridge above a steeper slope (photo of the triggering track and crown). While the avalanche was initiated in wind-loaded terrain, crowns opened up in apparently sheltered terrain as well (photo at right/above).

    Where is it? The depth of these weak layers varies from slope to slope, but it's safe to assume that they exist on most slopes. The sensitivity will be amplified in wind-affected terrain (picture to right/above) in more exposed terrain. It is also possible to trigger slides in more sheltered locations as well.

    How can you recognize it? Shooting cracks and collapsing are clear signs of an unstable snowpack.Natural and human-triggered avalanches will offer guidance on what type of terrain and slopes these avalanches are likely to be triggered on, but it's safe to assume that they exist on many slopes.  It might take some digging into the snow to reveal previous wind-affected layers that the new snow has masked in more sheltered locations. 

    How can you manage it? Persistent weak layers can fail unpredictably and break significantly wider and deeper than you might expect, producing much larger avalanches. Today I recommend you choose simple, conservative terrain to play in. Pay close attention to the terrain around you and what you are connected to in slope steepness. The combination of a recent large natural avalanche, an ugly snowpack structure, and unstable snowpack test scores is plenty of evidence to keep me out of big, steep, complex avalanche terrain.

    (2/28/2023) NE face of Copper Mountain at 8,400'. This avalanche appeared to be remotely triggered by a skier from above. This crown in sheltered terrain points to the potential for encountering avalanche problems outside of areas that are obviously affected by the wind.

  • Wind Slabs

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

    What is it? Recent snow and winds have created sensitive 1-2 foot thick slabs in exposed, upper-elevation with wind-affected snow.

    Where is it? These slabs will be the largest and thickest at upper elevations. Be on the lookout for wind slabs near ridgelines and on the sides of mid-slope features like gullies and ribs.

    How can you recognize it? Cracks shooting out from your skis or sled and collapsing clearly indicate instability. Look for ripples in the snow, dunes capping ridgelines, and drifting along gulleys or chutes' sides. Wind-deposited snow will be stiffer and keep your skis or snowmobile on or closer to the surface. Some of these slabs might be masked by recent snow and be more hidden.     

    How can you manage it? Wind slabs that fail can effectively trigger deeper weak layers described above. Seek more sheltered locations and follow the terrain management listed in problem #1.

    (2/28/2023) This large avalanche was observed on a N aspect of Copper Mountain near Banner Summit. The crown extends into terrain that is mostly sheltered from the wind.

Avalanche Discussion

Over the last 48 hours, I have documented at least 50 natural avalanches from Hailey to the Sawtooth and White Cloud mountains. Triggered avalanches have increased as well. They ranged from small to large avalanches and landed on most sides of the compass. Some showed the classic signs of a persistent slab, with crowns extending wide and wrapping through terrain features. All undoubtfully failed on some form of a weak layer, whether it needed the help of wind or not. 

Recent small storms built up a slab over fragile, weak layers that grew in the January and February droughts. The sensitivity of this slab increased with every storm that brought more wind and snow until it met its breaking point. Now that slab is well established across all of the Forecast zones. 

Terrain management becomes crucial to avalanche avoidance when triggering slides are likely. Consider the slopes you are connected to when a persistent slab exists in the snowpack. Traveling on slopes that aren't steep enough to avalanche will significantly reduce your chances of triggering an avalanche. Be hyper-aware of the slopes just steep enough to slide and connected to those lower-angle ones you have your sights playing on. A small pocket of steep terrain can be enough to get snow moving and connect to lower-angle terrain, causing a bigger avalanche. 

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