Bulletin d’avalanche

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Thu
Alpin
2 · Modéré
Limite forestière
1 · Faible
Sous la limite
1 · Faible
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Points saillants

Triggering an avalanche on weak layers buried 2-4 feet deep remains a possibility on very steep, rocky, wind-affected slopes at upper elevations. Smaller avalanches are also possible in areas with fresh wind-drifts, especially in the White Cloud Mtns where more snow fell over the weekend. 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    Early-season persistent weak layers (facets and depth hoar) in the lower snowpack are widespread throughout the Galena Summit & Eastern Mtns zone. Given the lack of snowfall in recent weeks, most slopes are tipping onto the stable side of the "stability seesaw." But, triggering a large avalanche on these deeply buried layers could result in severe consequences.  

    The chances of triggering a big persistent slab avalanche decrease a tiny bit each wind-free day it doesn't snow, but it remains possible in terrain with the following characteristics:

    • Steep: Slopes in prime-time avalanche terrain around 35-45 degrees.
    • Wind-affected: Heavily wind-loaded by past or recent wind events.
    • Alpine flavor: Complex terrain with scree piles, rocky ribs, and cliff bands. help to create lots of thin spots on the snowpack where weak layers are closer to the surface.

    Read more about why these slopes are particularly hazardous in the Forecast Discussion below.

    ADDITIONAL DISCUSSIONSki guides and other observers report encountering isolated, small wind slabs in exposed terrain near ridgelines. The slabs and drifts buried a variable old snow surface, including wind-hammered snow, crusts, facets, and about anything else you can imagine; while the drifts will be well-bonded to the underlying snow on some slopes, you may be able to trigger pockets of unstable snow on others. 

Avalanche Discussion

The winter of the haves and the have nots continues. If you frequently ski or ride in this zone, you know that you are in the latter category. The recent storm brought 4" of snow to the White Clouds, 1" to the Boulders and the Galena Summit area, and nothing at all to the Pioneers.  This pattern has been present for much of the winter and has prolonged the persistent slab problem that we're stuck with. For weeks, we've been warning you about the sort of terrain where you are likely to encounter this sort of problem: steep, wind-affected, and alpine. Let's take a minute to look at why these sorts of areas are more problematic.

  • Steep: As a slope gets steeper, gravity is pulling down more intensely on the slab. Slopes in the 35-45 degree range are at the sweet spot where it isn't so steep that the snow just sluffs off, but it is steep enough for gravity to have an appreciable downward force on the snowpack. 
  • Wind-affected: The wind plays two roles to increase the likelihood of triggering slides: in commonly scoured areas, the snowpack is thinner and the weak layers are closer to the surface where you have better "access" to them. In typically wind-loaded terrain, a stiff, dense slab is still stressing the weak snow underneath. Oftentimes these areas exist on the same slope, creating a scenario where likely trigger points are adjacent to meaty slabs. Hmmm.
  • Alpine flavor: As you move up in elevation, the terrain tends to get steeper and more wind-affected. Also, the alpine environment has lots of scree piles, rocky ribs, and cliff bands. These features help to create many areas with thinner snowpacks where weak layers are closer to the surface and easier to impact.

Spend some time scrolling through our media gallery and look at some of the deeper avalanches that we've been seeing this season. Try to identify these characteristics on slopes that have already avalanched. Then, as you are out in the backcountry, see if you can find slopes that have similar characteristics that haven't avalanched. These are exactly the types of slopes where you are most likely to encounter this problem today. The likelihood of encountering this problem isn't high, but the consequences sure are. 

Régions couvertes