Boletín de aludes

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Mon
Alta montaña
3 · Notable
Límite del bosque
2 · Moderado
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

The combination of new snow and wind is stressing weak layers buried 1-4 feet beneath the snow surface. Triggering a large avalanche is most likely on recently wind-loaded slopes, but is possible in wind-sheltered terrain as well. Avalanches can be triggered from gentler terrain 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
    Possible
    Tamaño
    1.5–2.5

    A complex patchwork of weak layers exists in the upper 1-4' of the snowpack. Yesterday, skiers in the Smiley Creek drainage reported triggering a large slide that broke 2 feet deep in wind-sheltered terrain. This was the fourth reported human-triggered avalanche involving these layers in the past 5 days. On slopes that face away from the sun, you'll find layers of surface hoar and weak facets. On slopes that face the sun, you'll find crusts with facets on top, and some spotty surface hoar mixed in. It's a safe bet that most slopes have one or more of these weak layers.

    The likelihood of triggering a slide on these weak layers depends on how deeply buried they are and the nature of the slab on top of them. Weak layers closer to the surface are easier to impact with your weight. Deeper weak layers are harder to impact, but the resulting slide will be much larger and more destructive. You're most likely to trigger avalanches on slopes where the wind has formed drifts or slabs or stiffened the snow at the surface (example). But, as yesterday's slide in Smiley Creek illustrates, these avalanches are also possible in sheltered terrain.

    Pay close attention to the snow you are moving through: cracking and collapsing are obvious signs of instability. But, don't expect to get direct feedback today.  Persistent slab avalanches behave in ways that catch experienced backcountry travelers off guard. The first sign of instability may be an avalanche that you trigger. These slides can break wider than you expect and can be triggered long distances away from steeper slopes. 

    ADDITIONAL DISCUSSION: Weak snow exists near the base of the snowpack. Triggering slides on this snow is unlikely, but the possibility can't be ruled out in steep, rocky, wind-affected alpine terrain. Slopes like these have variable snow depths, and thinner snowpack areas allow us to more easily impact deeply buried weak layers.

    (1/12/2023) A small, likely skier-triggered avalanche near Galena Pass. Two sets of ski tracks were observed near the crown. The avalanche released on a thin layer of facets sitting atop a crust. NE aspect at 8,800'.

  • Wind Slabs

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

    Yesterday, Soldier Mountain Cat Ski triggered large avalanches involving fresh wind slabs using ski cuts and explosives. Southerly winds picked up speed last night and slabs continued to grow in size and distribution. Expect to find reactive wind slabs today, some of which may produce slides large enough to bury you. 

    Look for these slabs near ridgelines and in mid-slope terrain features like gullies. Places like this slow the wind down and force it to drop whatever snow it is carrying, building slabs in the process. Pay attention to how deep and how dense the snow you are traveling in is. If the snow depth and density increase you are likely traveling through a fresh slab. Cracks shooting out from your skis or machine clearly indicate that you've found an unstable slab. Triggered wind slabs can step down to the weak snow described above, creating a much larger, more dangerous avalanche. 

Avalanche Discussion

HOLES IN THE MAP

I'm writing today's forecast with a few key weather stations down. The storm parade that is whacking the west coast has brought a seemingly unending stream of moist air into our region. Tiny, supercooled water droplets crystalize on objects when they run into them. Unfortunately, this means that our weather stations can become covered in rime, which compromises their function. This leaves me with a murkier picture than I'd like to have this morning.

Of course, as backcountry travelers, we are used to unclear pictures. We never quite know what we will find when we head into the mountains. Its worth spending the time to identify what we know and what we don't know. This helps build a better picture of what we will find in the backcountry today. Let's start with the knowns. Yesterday, large human-triggered avalanches were reported in the Soldiers and in the mountains above Smiley Creek. These occurred in both wind-affected and wind-sheltered terrain. That's some pretty strong evidence of instability right there. We also know that we have multiple weak layers in our snowpack, and that these weak layers have produced and continue to produce large avalanches. That's not a pretty picture.

And how about the things we don't know? This list is long, but we can touch on the basics. We don't know exactly how much snow has fallen where we are headed and we don't know exactly how much the wind has transported it. Fortunately, we can get a good sense of these things as we're moving through the mountains. Importantly, we don't know how much this new snow is affecting the layers of weak snow buried in our snowpack. These weak layers vary from place to place, as does the load on top of them. We do know that we are adding stress to these layers with new snow and wind, we just can't say with certainty how close we are to the tipping point. 

When you head out into the mountains today, take the time to recognize that the snowpack you are dealing with is complex, and filled with many more unknowns than knowns. These are the times when experienced backcountry travelers can get surprised. Unfortunately, the backcountry environment is unforgiving and we pay a high price for making mistakes. I'm dealing with this complexity and uncertainty by keeping my terrain choices simple. I'm paying close attention to the consequences of triggering an avalanche in the terrain I'm in. Today is a good day to dial back your ambitions and enjoy the gift of fresh snow in simple, gentle, easy-to-manage terrain.

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