Bulletin d’avalanche

Salt River and Wyoming Ranges

Bridger-Teton Avalanche Center
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Danger d’avalanche

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

Points saillants

Large avalanches involving layers of weak snow buried 1-3 feet beneath the surface are most likely in steep, wind-affected terrain, but are possible in sheltered terrain as well. Some of these types of slides can be triggered from long distances away from steeper slopes. You can significantly reduce your risk of triggering avalanches today by sticking to gentler terrain sheltered from the effects of the wind. Reduce your risk with cautious route-finding and assessing the snow you are riding on.

Problèmes avalancheux

  • Persistent Slabs

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

    Weak, faceted snow from November exists in layers at the base as well in the middle of the snowpack on most mid to upper-elevation slopes. Significant storms in December built a dense 2-5' thick slab on top of these layers.  In wind-exposed, upper-elevation, and rocky areas, the wind over the past several days has continued to add more load to the buried weak layers. In this sort of terrain, shallow spots where you could impact the weak layer are more common. Southerly aspects remain shallower, and you are more likely to impact these layers, but weak snow is not limited to this aspect. 

    These persistent weak layers are still showing sensitivity, but are becoming more stubborn as they get buried deeper in the snowpack. This is especially true with the November facets. Surface hoar and near surface facets from early December aren’t buried as deeply and continue to remain sensitive to human triggering. Several recent avalanches have been larger and on deeper layers, which is giving us some bullseye feedback. Limited field time in such a large zone adds uncertainty to how these layers adjusted to the recent storm cycle, and where exactly they are--and aren't. 

    (1/1/2023) Recent large natural avalanche on Angle Mountain at Togwotee Pass. 

  • Wind Slabs

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

    While you are most likely to find large, sensitive wind slabs at upper elevations, that isn't the only place they exist. Moderate winds build slabs down into middle-elevation terrain, and winds blowing from unusual directions (north and east) build slabs in unusual places. These will likely be 8 inches to 1 foot in depth. Yesterday I observed fresh slabs in the Greys River and larger cornice failures along ridgelines. Some of these slabs were on top of a rain crust found up to 9,000 feet. Though winds have eased overnight and less snow is available for transport, many of these wind slabs will remain reactive to your weight today. If you're traveling through thicker snow or see cracks around your feet, skis, or machine, you've found a wind slab. Even small avalanche terrain can have severe consequences where there are terrain traps like creek beds, and fast transitions from steep slopes to flat terrain below. 

    (1/2/2023)

    Cornice failure and subsequent small soft-slab avalanche on anE aspect at 8000' in the Snake River Range.

    Photo: Antonioli

Avalanche Discussion

Perception vs Reality

We all travel in the mountains with perceptions and biases as to what is happening in the snow around us. Though these two things have no correlation to the actual risk of avalanches in a particular place, they are intertwined in the human element of traveling in avalanche terrain. When moving in the different snowpacks in different areas of each range, I try to hedge my perceptions in cold hard data. Even with trends of persistent instabilities tapering in many locations, checking the snowpack before committing to steeper terrain (especially on aspects that have highlighted themselves as concerning in the past) is the only way to assess many of these problems. Either they are there, or they are not, but you have to dig in (literally and figuratively) to actually trend your perception towards the reality of what is happening with the snow in a given location. The process of continual assessment and re-assessment helps me wrap my head around my own biases and penchant for just seeing what I want to see. If you choose to enter avalanche terrain without any additional assessment each day, you choose to accept a very wide range of outcomes.  

All danger is not equal, and the spectrum of one hazard rating can be very broad. Our goal is to provide you with more nuance to conditions that may be oversimplified by a given avalanche problem and danger rating. The mere presence of buried persistent weak layers, even when deemed stubborn or not widespread, adds an element of complexity and unpredictability to snowpack assessment. The avalanches they produce tend to be larger and more destructive. But even with persistent layers, stability does improve slowly over time. If you avoid very steep, wind-affected slopes, and shallow slopes—especially those at upper elevations—you can dramatically reduce your chances of triggering an avalanche. 

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