Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

Thu
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

Conditions are tricky. You can find slopes where you can trigger an avalanche big enough to bury a person, but you may not see any signs the slope is unstable before triggering the avalanche. Avalanches are both largest and most likely at upper elevations and on shaded middle elevation slopes. 

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–2.5

     Some details on our tricky Persistent Slab avalanche problem:

    What and where is it? You could trigger 1.5-2.5 foot thick avalanches that fail on buried persistent weak layers—sugary facets or crust + facet combinations—near the bottom of the snowpack. Until proven otherwise, assume these old, weak layers of snow exist on all upper elevation slopes and on middle elevation slopes facing the northern half of the compass (W-NW-N-NE-E aspects).  Slopes where the wind recently formed drifts are especially suspect.  

    How can you recognize it? The old crusts and sugary facets are easy to feel with your hands, ski pole, or snowmobile track (see photos and videos below). You may not see obvious signs of instability like recent avalanches, snowpack collapsing, or cracks shooting out in front of you until it's too late.

    How can you manage it?  Sadly, the only surefire way to manage this problem is by avoiding avalanche terrain where more than about a foot of denser snow lies above the weak, older crusts or facets. Short of that, you can reduce your risk by avoiding large avalanche paths and those with ugly consequences if you are caught in a slide. Persistent Slab avalanches can break wider and higher on slopes (above you!) than you might expect. You could remotely trigger avalanches from gentler terrain below, above, or to the sides of steep slopes. 

     ADDITIONAL DISCUSSION: Recent snow showers and wind may have formed thin, fresh wind slabs in exposed upper elevation terrain. While small, these slabs could be very easy to trigger due to the weak snow (facets with or without a crust / surface hoar) buried beneath them. 

Avalanche Discussion

We haven't observed fresh avalanche activity in 10 days, but we're still spooked to ski or ride most large avalanche paths. Why? Lingering persistent slab instabilities are frustrating and challenging. You may not experience collapsing or cracking before triggering an avalanche, and you can ski or ride many slopes without triggering an avalanche. But, accurately assessing the stability of a given avalanche starting zone is currently difficult for the most seasoned professionals or recreational users.  

Recent observations: We're seeing a subtle decrease in reports of significant collapsing (view graph here) and a lack of recent avalanche activity. However, take that with a big grain of salt. Few people (potential triggers) are out playing in the mountains, and many of the easily accessible avalanche paths already ran this season (view Avalanche Occurrences here). Additionally, the little bit of new snow and wind loading in recent days is keeping us in a holding pattern.

If you plan to "boldly go where no one has gone before [so far this winter]" and venture into terrain free of ski or sled tracks, U.S.S. Enterprise Captains James T. Kirk and Jean-Luc Picard of Star Trek fame would encourage you to be cautious and follow your intuition; if you're having second thoughts, save it for another mission. Consider the consequences of being caught in an avalanche before committing to skiing or riding steep terrain where the persistent weak layers exist.  

Régions couvertes