Boletín de aludes

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Wed
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2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

The likelihood of triggering an avalanche is greatest in the western portion of this zone (Soldier Mountains), where much more snow fell yesterday. Triggering a dangerous avalanche is most likely on steep, wind-affected slopes. Large natural and human-triggered avalanches were reported in nearby zones this weekend on slopes with exactly these characteristics. Fresh wind slabs will be sensitive to your weight and may trigger deeper weak layers in the snowpack as they travel downslope. Avalanches are much less likely in areas that are sheltered from both current and past wind. Avalanches can be triggered remotely—from below, above, and to the sides of steeper terrain.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    The weak snow buried near the ground continues to be the primary avalanche concern in this zone. While encountering a wind slab (described below) is more likely, particularly in the Soldier Mountains, any wind slab you trigger has a good chance of "stepping-down" to the weak snow near the ground. This layer has produced both human triggered and natural avalanches in nearby zones in the past few days:

    • Saturday, a rider between Wells and Dollarhide Summits triggered an avalanche on a steep, heavily wind loaded slope (photo at right).
    • Saturday, a skier on Titus Ridge intentionally triggered a large avalanche. The slide initiated as a stiff wind slab that formed during last week's wind event and then "stepped down" to the December weak layer. Photos and more details are available here. I looked at the slide that afternoon—watch the video I made.
    • Sunday, Sun Valley Heli reported seeing a recent large, natural avalanche that failed near the Baker divide, likely involving this weak snow (photo here).

    The depth of the snowpack is highly variable in this zone. This is important because the more deeply this weak snow is buried the more difficult it is to impact. Conversely, in areas where the snowpack is thinner, the weak layer is much more "accessible" to a skier or rider. Last week's prolonged wind event stripped many slopes (bringing the weak layer closer to the surface) and deposited hard slabs on many others (adding weight to the weak layer).

    Snowfall over the past few days has masked the obvious signs of what happened during the wind event, making it nearly impossible to determine what happened during that event on any given slope. This high degree of variability has created a snowpack who's behavior is difficult to predict. This fact has kept many experienced skiers and riders from entering into consequential avalanche terrain, despite the gradually decreasing danger. 

    So what sort of areas should you be most worried about right now? The avalanches described above share a number of characteristics: they failed in steep (over 35 degrees), rocky, wind-affected terrain. This is exactly the type of terrain where you are most likely to encounter this problem today. 

    (2/12/2021) This avalanche was triggered by a rider NE of Wells Summit in the Soldier & Wood River Valley zone. The slide broke around 40' wide and carried the rider about 100 yards. A section of the cornice also released in the slide.

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Yesterday, Soldier Cat Ski guides reported that 6-10" of new snow fell at upper elevations in their terrain, with wind speeds increasing later in the day. They were able to trigger small, fresh wind drifts with both ski cuts and explosives. Similar slabs may be reactive to your weight today. Traveling east in this zone towards the mountains above the Wood River Valley, significantly less now fell and the wind slabs will be smaller and less reactive there. You are most likely to encounter sensitive wind slabs today in areas where more snow fell. Remember that even small slides can have high consequences if they carry you through rocky, treed terrain or push you down into a terrain trap like a gully or a creek bed.

Avalanche Discussion

NEW SNOW AND OLD SNOW

Over the past few days we've seen a slow trickle of snowfall across our region. As this new snow has gradually stacked up, we've enjoyed a significant improvement in skiing and riding conditions. The stiff wind slabs and icy crusts that built during the extended wind event are covered up with soft, fluffy powder and I'm not hearing anybody complain about that. From a snow stability and avalanche danger perspective, we've seen our concerns diverge into two sets of issues that we should be thinking about as we travel in the mountains today:

  1. NEW SNOW: The mountains south and east of Galena Summit have picked up 3-10" of new snow in the past few days, while the mountains to the north and east have stacked 18-24". The winds have been at work at upper elevations, generating a few batches of wind slabs over this period. The freshest batch of slabs will be the most sensitive to triggering today, but older slabs shouldn't be ignored. As you travel down into more wind-sheltered middle and lower elevation terrain you will find better riding and skiing conditions in addition to less dangerous avalanche conditions. That sounds like a good place to be! In areas where more snow has accumulated, you may also encounter some loose snow issues today. Dry loose avalanches (sluffs) will be on the menu in steep terrain. And, if the sun comes out for long, expect to see some natural loose snow avalanches initiating on slopes that are being warmed by the sun. 
  2. OLD SNOW: Everything that is going on in the upper portion of the snowpack is taking place on top of a foundation of weak snow. In our northern areas (Banner Summit and Sawtooths) this weak snow is now buried under a 4-6' thick, very dense slab of snow, which has become difficult to impact with the weight of a skier or rider. Further south, where the slab of snow is thinner, this layer is more accessible and the possibility of triggering a slide on this weak snow is much greater. It is easy to forget about this deeper issue when we are focused on the new snow issues and there is great powder skiing and riding to be had. But, unfortunately we are a long ways from being out of the woods on this one.

The snowpack is complex and tricky this season and in order play in the mountains safely we need to give it the respect that it demands. My primary goal is always to return home safely at the end of the day. After all, I can't go powder skiing tomorrow if I don't make it out safe today. Keep it tight my friends, and enjoy the fresh snow!

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