Bulletin d’avalanche

Tetons

Bridger-Teton Avalanche Center
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Danger d’avalanche

Thu
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Conditions remain dangerous. Triggering a large avalanche is likely on steep slopes in the upper elevations. Skiers and riders should choose low-angle terrain that isn't threatened by steeper slopes above. People have triggered avalanches—from below, above, and to the sides of steep slopes—each of the last five days.

A large avalanche triggered by several parties on Mt. Taylor two days ago illustrates this hazard. Skier-triggered avalanche on Mt. Taylor

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–3

    The past week's historic storm has added a significant slab to a widespread persistent weak layer that is now buried around 2-3+ feet deep in this zone. A cycle of natural avalanches occurred, and human-triggered avalanches have been reported each of the last five days. Observers continue to report avalanche activity, collapsing and/or cracking of the snowpack, and high winds in the upper elevations. We have received enough recent snowfall that these slabs could produce a large enough avalanche to bury you (and possibly your car) and break 3-4+ feet in depth. Additionally, there is the possibility of a slide stepping down into the deeper persistent weak layers described below. 

    WIND SLABS: A spell of moderate winds yesterday and overnight have created wind slabs on some exposed slopes. These new drifts are adding more weight to the persistent weak layer, and triggering one could step down deeper to become a much bigger avalanche.

    (1/31/2023)

    The complex crown of the skier-triggered avalanche on the south face of Mt. Taylor. 

    Photo: Antonioli

  • Deep Persistent Slabs

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

    Yesterday's investigation of the Mt. Taylor crown showed no involvement of the Nov. 27 layer and was isolated to the old/new snow interface (now deemed the Jan. 27 layer). That being said, this problem will remain on the table until more evidence has cleared it, particularly on the west side, where snowpack depths have remained shallower. Looking for evidence of shallower slopes in the middle and upper elevations, probing for snow depths, and digging in shallow areas can help identify if where you are recreating still has this problem. 

    Avalanches on this layer have become harder to trigger, but the resulting slide would be catastrophic. These weak layers may be more easily impacted by your weight at mid-elevations where the slab is thinner, or in rocky and/or wind-affected areas where there are shallower areas. Areas with the highest likelihood of triggering this layer are on the southern half of the compass above 8000’. 

    Avoiding terrain where both of these problems overlap is key.

     

    Crown profile showing Nov. 27 facet layer on the south face of Mt. Taylor.

Avalanche Discussion

At the risk of undermining any notion of expertise you may think I possess, I've made plenty of bad decisions in avalanche terrain. I'm eternally skeptical of myself. Not to a point that is paralyzing, but I think about how I think about everything- a lot. We are all fallible, and I find it best for my practice to own that and talk about it openly. How else does one receive feedback when the environment won't provide it? I usually seek it from friends, mentors, or any objective third party. I encourage you to do the same if you don't already. Triggering an avalanche is not great because it may injure or kill us, or others. But is also nothing to be ashamed of, particularly if we were striving to make the best decisions. It is an inherent part of playing the backcountry game, where feedback is so poor that plenty of bad decisions end in nothing happening, or sometimes even, great skiing. 

There hasn't been significant loading for several days, so are avalanche conditions becoming safer? The answer is an emphatic "No". There are two important points to consider:

1) The buried weak layer is especially bad due to a well-developed and widespread nature

2) This weak layer has received a rapid and large snowfall with increasing winds.

These factors, especially in combination, have produced an instability that could be long-lasting and unpredictable. Even as we head into a period of more stable weather, I wouldn't be surprised if people are triggering avalanches a week from today. Throw human behavior into the mix, and one could argue that conditions are becoming more dangerous. As time goes by and the obvious signs of instability diminish, it requires more and more discipline to choose the appropriate terrain.

Régions couvertes