Boletín de aludes

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Wed
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
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

Avalanche conditions are dangerous. Triggering a large avalanche is likely on steep, wind-drifted slopes. New snow and wind are forming dangerous wind slabs and adding weight to buried weak layers in the top 3' of the snowpack. Reduce your risk by sticking to lower-angled terrain that is sheltered from the wind.  

Conditions will be most dangerous in the Soldier Mountains where more snow fell.

Problemas de aludes

  • Persistent Slabs

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

    New and windblown snow from the past few days is adding weight to multiple weak layers in the top 1-3' of the snowpack. These weak layers of facets, crusts, and/or surface hoar were responsible for a number of human-triggered avalanches around the start of the New Year.  Dry weather in early January gave these layers a chance to start stabilizing, but also formed new weak layers that are now buried beneath 12-16" of recent snowfall.

    The presence and strength of these weak layers vary greatly from location to location, but you can be reasonably certain that at least one weak layer is in play on most slopes. Trying to outwit the persistent slab problem by attempting to assess it on a slope-by-slope basis is a losing proposition. Triggering a large, persistent slab avalanche is most likely on exposed, wind-loaded slopes, but could also occur in steep, wind-sheltered terrain. The best approach is to take a step back, choose gentler slope angles, and let the dust settle from the recent storm loading. 

    ADDITIONAL DISCUSSION: While triggering slides on faceted snow deep in the snowpack is unlikely, it can't be ruled out in steep, rocky, wind-affected alpine terrain. Slopes like these have variable snow depths, and thinner snowpack areas allow our weight to more easily impact deeply buried weak layers.

    (1/1/2023) Debris from a very large avalanche that was remotely triggered above Hyndman Creek in the Pioneer Mountains. This slide failed in a heavily wind loaded area and very likely involved a persistent weak layer. It covered the summer trail with a pile of debris that was 100-150' wide and 4' deep.

  • Wind Slabs

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

    Since Sunday, most of our area has picked up  12-16" of new snow. If wind could be measured in the same manner, we received multiple feet of it. Weather stations near Galena Summit have recorded the highest winds, but all of our ridgetop sites have reported elevated winds over the past 48 hours. Yesterday I walked out Titus Ridge—always a fun place to be when the wind is howling and conditions are "western". I found large drifts up to 3' thick, and easily triggered a small wind slab avalanche by stomping atop a steep slope (video above/right). Wind slabs will be larger and more dangerous in the Soldier Mountains where more snow fell yesterday.

    Identifying wind-drifted terrain shouldn't be difficult today. Finding areas where the surface snow is thick or dense, or deeper than other areas, is clear evidence of wind-loading. Yesterday, I found that open slopes were either covered in rippled, dune-like drifts or scoured and wind-raked. Wind slabs will be big enough to be dangerous in their own right, but any triggered slab could step down to the deeper weak layers described above, producing a much larger avalanche. The travel advice is similar to the persistent slab problem: stick to lower slope angles in wind-sheltered terrain, and avoid steep, wind-loaded slopes.

Avalanche Discussion

Identifying the degree of uncertainty surrounding our knowledge of the avalanche danger is just as important and assessing the danger itself. The first step in evaluating uncertainty is identifying where it comes from—in other words, what don't we know? Here is a laundry list of some of the current sources of uncertainty, roughly from most to least uncertain:

  1. What is the distribution and sensitivity of buried weak layers in the top 3' of the snowpack?
  2. Where are is the deeply-buried November weak layer still a concern?
  3. How are these older weak layers responding to the new loading?
  4. Are newer weak layers buried by the recent snowfall becoming reactive?
  5. What are real-world storm totals since Sunday?
  6. How large and sensitive are the fresh wind slabs?

Once we've identified the sources of uncertainty, we ask ourselves: which of these can we reduce through additional observations and information gathering? Of these questions, which are the most answerable? Numbers (1) and (2) are tough ones. Only repeated observations over time and  in many places will help, and the observations over the past week haven't painted a complete picture. We may get answers to (3) when we get visibility and look at the pattern of avalanche activity from the recent storm. Numbers (4) through (6) seem to be fairly "answerable" questions and would be good objectives if you head into the field today.

The final question: once we've identified uncertainty and sought to reduce it as much as possible, how much is left? Today, a high degree of uncertainty remains due to the questions listed above. It turns out that we manage uncertainty in the same way as we deal with hazardous conditions—by choosing more conservative terrain. If we're not sure that conditions are safe, then we take a step back. In other words, it's either "Heck yes, or no way."

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