Bollettino valanghe

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Sawtooth Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Avalanche conditions are tricky. The first sign of instability you see may be the 2-4 foot thick slide you trigger. These avalanches can be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes. Choose simple, lower-angled terrain to reduce your risk.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    You could trigger a 2-4' thick persistent slab avalanche on buried weak layers (sugary facets or crust + facet combinations). This problem is worst on middle and upper elevation slopes facing W-NW-N-NE-E-SE. 

    Unfortunately, unstable slopes probably won't provide obvious signs of instability, like snowpack collapsing or cracks shooting out in front of you. Snowpack stability tests are likely to be inconclusive and are of limited use. Tracks on a slope don't mean it's safe. Avalanches can be triggered by the second, third, or fourth rider on a slope. In low probability/high consequence situations like this, there's a good chance the first sign of instability you'll see is the avalanche you trigger.

    The likelihood of triggering a slide is not that high, but the thick, dense slab makes the consequences severe. Persistent weak layers can fail unpredictably and break wider and higher on slopes than you might expect. You can reduce, but not eliminate, your risk by avoiding slopes steeper than about 35 degrees—especially large avalanche paths and those with ugly consequences if you are caught in a slide.

    ADDITIONAL DISCUSSION: Be on the lookout for sensitive slabs of wind-drifted snow at upper elevations. Steer clear of smooth pillows of windblown snow near ridgelines and mid-slope gullies. Loose snow avalanches are possible during periods of intense snowfall. They may also occur during brief periods of sunshine, especially in very steep, rocky terrain.

Avalanche Discussion

Today's avalanche conditions are tricky. Watch Ben's video to get a quick sense of what you're dealing with (video). While taken in the Smoky Mountains, this video shows the general setup that we're looking at across the forecast area; a dense slab of snow sits atop weak layers that were formed and buried in February.

This zone has a couple of things going for it. The slab is more uniformly thick, and the primary weak layer here appears to be less sensitive than in the rest of the forecast area. As such, triggering a persistent slab avalanche is less likely here than further south. Unfortunately, less likely doesn't mean impossible, and given the expected size of a triggered slide going for a ride will likely be unsurvivable. We often refer to this type of scenario as low likelihood/high consequence. In other words, we may be able to get away with a lot... until we don't.

The way we travel needs to reflect this uncertainty and unpredictability. The frustrating reality is that many slopes have the right ingredients to slide, and there's no way to know if your chosen path will hit the sweet spot that releases a deadly avalanche.

You can effectively keep out of harm's way by avoiding avalanche terrain, including the base of slopes greater than 30 degrees. Short of avoidance, you can reduce your risk by choosing to steer clear of shadier, more northerly aspects and by sticking to simpler, lower-angled terrain. In this video from the Sawtooths, Karl Birkeland, Senior Avalanche Scientist from the National Avalanche Center, describes the snowpack conditions he observed and how they factored into his terrain selection for the day (video).

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