Bulletin d’avalanche

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Sun
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Large avalanches failing on weak snow near the ground remain a worrisome possibility here. This problem is at its worst in wind affected terrain at upper elevations and on shaded middle elevation slopes (W-NW-N-NE-E). Slides can be triggered from a distance away from the slope that avalanches and may break wider than you'd expect.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    The recipe for avalanches (slab+weak layer) exists in many places here. Weak snow forms the base of the snowpack on upper elevation and shaded middle elevation slopes (W-NW-N-NE-N). If you dig down, you'll find weak facets and crust+facet combinations buried underneath a dense, 1-2+ foot thick slab of snow. This combination is capable of producing large, destructive avalanches, and has been the primary driver of avalanche danger this season. 

    As you're traveling, pay attention to the feedback the snow is giving you. Cracking and collapsing are clear signs that the snow you are moving through is unstable. Heed these warnings, but don't let an absence of them lure you into complacency. You can significantly reduce your risk of tangling with a large avalanche by avoiding slopes where this weak snow exists at the base of the snowpack.

    This persistent slab avalanche was observed near Galena Summit on Sunday, 12/10. It failed on a N-facing slope at 9,300'. The crown spans nearly 500 feet of terrain and is an estimated 1-1.5 feet thick. This failed on a layer of weak snow that underlies the snowpack on all upper elevation slopes and many shaded, middle elevation slopes.

    Photo: Ben VandenBos

Avalanche Discussion

TESTING OUR PATIENCE

We are dealing with a persistent slab problem across our forecast area. Ask any experienced rider, skier, or snow professional — they'll be sure to tell you that persistent weak layers are their least favorite avalanche problem to deal with. Why is that? Well, for one...because they are so persistent!

In general, avalanches are most likely during and shortly after loading events. When new snow bonds well to the snow underneath, the likelihood of triggering avalanches can decrease quickly. However, when new snow falls on persistent weak layers, this decrease in the likelihood of triggering slides happens at a much, much slower pace. This is where we find ourselves today.

The snowpack is gradually becoming accustomed to the weight of the slab, but obvious signs of instability like collapsing of the snowpack continue to be reported with every observation that rolls in. This collapsing process is the first step in avalanche release. So what do we do about this? That's where the patience part comes into play. If you head into the backcountry today, be ready for your patience to be tested. You'll fight your way through some ugly terrain as you work your way up to where there is enough snow for riding and skiing. When you finally battle through the thick bush at low elevations you'll emerge into a much snowier world. Your eyes will be drawn to beautifully snow-covered pieces of terrain, the exact slopes where the persistent slab problem is at its worst.

If you choose to ski or ride steep avalanche terrain in areas with weak snow at the base of the snowpack, you are rolling the dice. There really isn't a better way to put it. There is a chance that you ski your desired line without a bad outcome, and there is a chance that you trigger a large destructive avalanche that carries you downslope through exposed rocks and trees. Exercise your patience today. The season has just begun and we will find windows of better stability and better coverage at some point. 

Régions couvertes