Boletín de aludes

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Thu
Alta montaña
4 · Fuerte
Límite del bosque
3 · Notable
Bajo el límite
3 · Notable
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Desactualizado: este boletín caducó 7 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Snowfall and strong winds will make natural and human-triggered avalanches likely. Avoid traveling on and below steep slopes where the wind is drifting snow. Large avalanches are also possible in sheltered terrain where buried layers of surface hoar or sugary facets exist. Avalanches may be triggered remotely—from gentle terrain above, below, or to the sides of steep slopes.   

Problemas de aludes

  • Persistent Slabs

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

    Snowfall and wind-drifting may overload multiple weak layers buried 1-2 feet deep in the snowpack. The size and chances of natural and human-triggered avalanches will increase as the storm progresses. Some avalanches could be 2-4 feet thick and hundreds of feet wide.  

    Be very careful traveling on and below all steep slopes. Poor visibility will make it nearly impossible to see what’s above you, or even in front of you. Slides may be triggered from a distance – including from the sides or below a slope.

    This problem will be most pronounced in the White Clouds where more snowfall is expected.

  • Wind Slabs

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

    Strong winds and moderate snowfall will make natural and human-triggered avalanches likely in wind-loaded terrain, including on slopes with no glaring, buried weak layers. The wind slabs will increase in size and become widespread in upper and some middle elevation terrain today. Expect to find soft and hard slabs both near ridges and lower on slopes. At lower elevations, large drifts and wind slabs will be more isolated.  

    The wind slabs are forming on a variable snow surface. Expect stability to quickly change on different aspects and elevations. Poor visibility will compound the situation. Avoid wind-loaded avalanche terrain. 

    This problem will be most pronounced in the White Clouds where more snowfall is expected.

Avalanche Discussion

Over 20 years ago, a sage ski area and highway avalanche forecaster gave me some of the best advice I’ve ever received: “you will be surprised by some slopes avalanching, but you don’t want to be surprised by what [weak layer] they fail on.” Although his advice was geared towards slope-scale forecasting (e.g. is this slope safe to ski), I still strive to always know what snowpack layer(s) will fail during the next storm. 

In the past couple of weeks, our snowpack became quite complex; the “chief concern” changes from drainage to drainage, aspect to aspect, and as you move up or down in elevation. Also, gauging the sensitivity of individual weak layers is not as straightforward as before Christmas. 

The suspects:

  • Surface hoar from early Dec, now buried 1-2 feet deep
  • Depth hoar (Sept and Oct snowfall that turned into large, weak, sugary grains)
  • Where the snowpack is less than about 18” deep, the entire pack has become weak and faceted
  • On some sunny slopes, there are crusts and facets buried 6-12” above the ground
  • Yesterday’s snow surface: a mix of surface hoar, crusts, crusts + facets, slick wind-polished alpine surfaces, and some decomposing powder that actually looks OK  

What can we focus on to navigate this complex scenario? KISS (Keep It Simple Stupid/Scotty). Some simple things to consider:

  1. Loading: On steep wind-loaded slopes and any steep slopes with around a foot or more of new snow, I expect the rapid nature of the large loading event to “find” a weak layer to fail in many paths. I’ll pass on traveling in avalanche terrain until the snowpack has some time to adjust to the new load and we identify avalanche activity patterns. Where less new snow falls, I will still avoid all consequential avalanche paths - those with trees in them, terrain traps at the bottom, etc.
  2. Avalanche size: the surface hoar and depth hoar layers are 1-2 feet deep on many slopes. Add the snow from this storm, and you have a 3-foot thick slab on many slopes. No thanks - I’ll avoid avalanche terrain where those weak layers exist.

Have fun playing in the fresh snow, but don’t try to outsmart the snowpack during today’s storm.

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