Bulletin d’avalanche

Salt River and Wyoming Ranges

Bridger-Teton Avalanche Center
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Danger d’avalanche

Thu
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

New snow and consistent winds will stress deeper snowpack layers. To significantly reduce the chance of triggering a large avalanche, avoid steep slopes where the wind has drifted the new snowfall, formed slabs, or stiffened the snow surface. Larger avalanches involving layers of weak snow buried 1-3' beneath the surface are most likely in upper elevation, wind-affected terrain, but are possible in sheltered terrain. Utilize cautious route-finding and assess the weak layers buried in the snowpack you are riding on.

Problèmes avalancheux

  • Wind Slabs

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

    Continued new snowfall will produce sensitive wind slabs at upper elevations. Moderate to gusty winds will build slabs down into middle-elevation terrain. These will likely be 8 inches to 1 foot in depth. Yesterday, Alex and I observed several old (and deep) avalanche crowns at Togwotee Pass around Angle Mountain and Breccia Peak. Winds above 8'000 feet were crafting fresh slabs, and plenty of new snow was available for transport. 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.  

    Wind-affected areas can be identified by pillowed drifts or dunes, cornices along ridge crests or running down sub-ridges, and/or stiffened snow surfaces.

    (1/2/2023)

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

    Photo: Antonioli

  • Persistent Slabs

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

    Consistent snowfall is adding gradual load to deeper layers. 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. 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. 

    Except for areas threatened from above, the danger is much lower at low elevations, below about 7500' where rain saturated the shallow snow and colder temperatures have since frozen it solid. 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.

     

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

Avalanche Discussion

When dealing with avalanche hazards and problems, it is important to understand the context of thinking in probabilities. With hazard ratings not changing recently, it is easy to get message fatigue and not really think about how the snow is still constantly changing. When snowfall is consistent and gradual, the snowpack may not really show its cards. This puts us, as backcountry users, in a particularly low-feedback scenario.  Avalanches occur and get covered up by more snowfall, are blown in by the wind, or happen overnight, and it's important to understand that we see such a small spectrum of what happens in a range on a given day or storm cycle. Even with so many user observations--which are helpful to the community and we are incredibly grateful for--many have a bias toward frequented locations and may be less representative of deeper or less visited areas. Let's dig into a moderate hazard rating, which has been at the mid-elevations for some time. Moderate, by definition, means human-triggered avalanches are possible. I find it helpful to think of this possibility in a different context. If I offered to give you a ride in my car on an icy pass but mentioned that I wasn't feeling 100% and it was possible that I may drive off the road or into another car, how would you feel? Would you feel comfortable just hopping in and trusting I would be fine? Or would that possibility raise a few questions and require you to assess me differently? [Side note-I'm actually a good driver]. 

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 unreactive and not widespread, adds an element of complexity and unpredictability to snowpack assessment. With our current conditions, the places where you could trigger an avalanche on a persistent layer are becoming more and more isolated. But it's definitely not a free-for-all; if you go looking for trouble, you may find it.

Régions couvertes