Bulletin d’avalanche

Salt River and Wyoming Ranges

Bridger-Teton Avalanche Center
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Danger d’avalanche

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

Points saillants

You're most likely to trigger an avalanche on middle and upper elevations where wind and recent snowfall buried old weak snow. Avalanches may be triggered remotely -  from flat terrain above, below, and to the sides of steep slopes. Look for signs of stiffened or hollow-sounding snow, large drifts, and textured or cracking snow surfaces to identify wind-loaded slopes.

Problèmes avalancheux

  • Wind Slabs

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

    It remains possible to trigger an avalanche of stiff wind-drifted snow on NW - N - W - S slopes at middle and upper elevations. Recent strong sustained winds from the west/ southwest created slabs 2-3 feet thick on top of persistent weak layers. Due to the widespread nature of these weak layers - avalanches could be triggered remotely from low-angle slopes above, below, or to the side of steep slopes. Watch for signs of unstable snow such as shooting cracks or collapsing ("whoomph" sounds).  Textured snow surfaces, drifts, and cornices are visual indicators that winds have been transporting snow. Keep a close eye on wind-loaded terrain. 

     

    (12/18/2024) Here is a good example of wind-affected snow. This small slide broke to the ground on facets (2-3ft deep). A shallower wind slab also broke 8-10” deep. Note the textured surface of the snow indicating wind transport. 

  • Persistent Slabs

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

    The most recent storms brought 22-26" of snow to the Salt and Wyoming Ranges with over 2" of snow water equivalent. This new snow is consolidating into 1-2 foot thick slabs that are sitting on a variety of weak snow layers including facets, surface hoar, and crusts. These weak snow layers, which formed in early December, are widespread. The widespread nature of these weak layers means avalanches can be triggered on all aspects at middle and upper elevations. Your chance of triggering an avalanche is greater where wind has loaded the terrain with additional snow. These avalanches can be triggered remotely in surprising ways, breaking above, below, or in front of you. Warming temperatures today can change the characteristics of the overlying slab above weak layers and increase sensitivity. There may not be signs of instability before triggering a persistent slab avalanche. Use a wide safety buffer around steep slopes to address the uncertainty. 

    (12/17/2024)

    A slab avalanche failing on a persistent weak layer in the northern Salt River Range

    Photo: Bridger-Teton Avalanche Center

Avalanche Discussion

The most recent storms brought 22-26" of snow to the Salt and Wyoming Ranges with over 2" of SWE in the middle and upper elevations. This new snow fell on weak layers that developed from our early season precipitation. As the new snow consolidates, it's forming a slab that could be triggered by a human. These persistent weak layers are tricky to identify from the surface and often will show no signs of instability before collapsing and causing an avalanche. Taking the time to dig into the snowpack will help you understand their distribution. Remember, if you find hard snow over soft snow, you have the anatomy for an avalanche. These layers take time to adjust. Now is an excellent time to familiarize yourself with them while the snowpack is thin and easy to dig into. Lower elevations are rated 'Low' due to the absence of old snow. Much of the early season snowfall melted at the lower elevations before our most recent storm. Low danger does not mean no danger though, old weak snow may exist in isolated pockets of protected terrain at low elevations. 

We have also had recent sustained winds from the west/ southwest. In conjunction with our recent snowfall, slabs of wind-drifted snow have formed in the mountains. These avalanches will behave similarly to the persistent slabs, as they have both developed on the same weak layers within the snowpack. Pay close attention to terrain where snow has become wind-affected. More snow on these persistent weak layers increases your chance of triggering an avalanche. 

Additionally, pay attention to warming snow on steep southerly slopes today. Yesterday, high daytime temperatures and direct sun were producing rollerballs and pinwheels on steep roadcuts and exposed rock. We have similar temperatures today. Increasing temperatures can increase the sensitivity of layers within the snowpack. While not listed as an avalanche problem don't underestimate the temperature's effect on the snow. Even a small amount of wet snow can prove problematic. 

Finally, remember that our snowpack is still thin. Even with our latest snow - rocks, logs, and other hazards may lurk just beneath the snow surface. The good news is we are sitting right around average now for precipitation totals, with more snow on the way. 

 

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