Boletín de aludes

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Peligro de aludes

Tue
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
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

Small slabs of wind-drifted snow may be reactive to your weight today. Look for these in exposed middle and upper elevation terrain. Weak layers buried underneath dense, 2-4 foot thick slabs can produce much larger, more destructive avalanches. You aren't likely to experience signs of instability with these deeper weak layers—the first sign may be the large avalanche you trigger. Steep, rocky slopes receiving direct sunshine can produce loose snow avalanches. Choose simple terrain free of terrain traps to reduce your risk.

Problemas de aludes

  • Persistent Slabs

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

    What is it? A very dense, 2-4+ foot thick slab stands over buried weak layers of facets or crust + facet combinations. While these avalanches are getting harder to trigger, releasing these destructive beasts is not impossible. Watch the video to the right/above to understand this problem better.

    Where is it? Most slopes harbor these layers. You'll find crust + facet combinations on sunny slopes and small facets on shaded slopes. We are still tallying up the historical amount of slides produced by these weak layers (map, list). 

    How can you recognize it? The first sign of instability may be the large, destructive avalanche you trigger. Tracks on a slope don't indicate it is good to go. These slides may break much wider and further above you on the slope than expected. Unless you dig down to confirm the weak layer exists, you might assume the snowpack feels good under your feet or sled. And if you take the time to dig down, don't trust the results of your stability tests. They serve little help when dealing with such a dense slab overlying this weak layer. 

    How can you manage it? The only way to eliminate your risk of encountering one of these devastating slides is to avoid avalanche terrain and terrain exposed to hazard from above. I know that's not satisfying to hear. You can reduce your risk by avoiding slopes steeper than about 35 degrees—especially large avalanche paths and those with ugly consequences if caught in a slide. Remember that even small slopes can have high consequences when dealing with very dense slabs. These slides can be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes.

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–1.5

    What is it? Be on the lookout for both new and older generations of soft or hard slabs. Some slabs may be sitting over sugary, faceted snow, which can be more sensitive than your typical wind slab problem. 

    Where is it? These slabs tend to grow along ridgelines in upper elevations and further down the slope on the sides of gullies and ribs. 

    How can you recognize it? Look for shooting cracks exiting from your sled or skis or collapsing in the snowpack. These are signs of unstable snow. You can recognize wind-affected areas by stiffer or harder snow that supports your skis or machine and surface texture such as ripples, waves, or dunes. It may sound hollow or drumlike. 

    How can you manage it? In most places, these won't be big enough to bury you, but they can knock you off your feet and send you downslope at high speed. Steer away from avalanche terrain when encountering slopes with denser snow or signs of instability. Smaller triggered slides can be effective triggers for the weak layers described in the Persistent Slab problem above.

    ADDITIONAL DISCUSSION: Today's ample sunshine will trigger loose snow avalanches as the sun warms up the freshly fallen snow for the first time. These small avalanches can be effective triggers for wind and persistent slab problems mentioned above. The most likely spot to trigger these avalanches is below steep, rocky slopes facing the sun. They may run fast and far over the crusts on sunny slopes and can be found on steep, north-facing terrain. Avoid being on slopes in direct sunlight to minimize your chances of getting caught in these slides that can trigger bigger avalanches or carry you through cliffs, trees, gullies, or other terrain traps. 

Avalanche Discussion

The sun will be making a strong appearance today. Since we haven't seen much of this old friend, it will likely cause a widespread cycle of small avalanches on slopes that face the sun. But don't let this glaring problem be at the front of your mind when leaving the house. We still have the other unwelcomed guest lurking in the snowpack. These sun-induced avalanches will likely take the show, but the persistent slab shouldn't be left in your rearview mirror. The wind and persistent slabs are more likely to bury you in a large to unsurvivable avalanche. 

It's hard to believe that we are at the end of March. We've had far fewer days of sunshine than is typical this time of year. All of the recent snow isn’t going to react well to the strong effects of the sun. These loose snow avalanches will likely start failing as the sun rotates from the SE to S to SW. As these slides pick up speed and entrain more snow, they can release other larger avalanches, like wind slabs below cliff bands or persistent slabs that need an extra nudge of weight to release.

Accidents are more likely to occur on sunny days following snow storms. I know this storm isn’t the same size as a couple of weeks ago, but the western mountains have picked up a good amount of snow in recent days (see Storm Totals). As we continue to manage expectations of a low likelihood/high consequence avalanche problem, we face another influencer of instability: the sun. Stay off of steep, rocky slopes in direct sunlight to manage the loose snow avalanches. Avoidance is the only surefire tool to not mess with the persistent and wind slabs problems. Stable spring conditions will eventually make up our snowpack, but we are far from that structure right now.

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