Bollettino valanghe

Snake River Range

Bridger-Teton Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You could trigger a wind slab avalanche in upper elevation terrain—identify and avoid slopes with evidence of wind drifting. Loose snow avalanches could occur on steep slopes facing the sun as the day warms up. Larger avalanches that fail on weak layers buried 2-4 feet deep are possible and carry high consequences. Evaluate wind-drifted snow carefully and be prepared to move to low-angle terrain if you observe signs of instability.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Low-density snow from the past 48 hours will continue redistributing in light to moderate winds at upper elevations. N-NW winds have been blowing relatively lightly but consistently—including yesterday and overnight. Northerly winds often blow upslope, creating unusual loading patterns and cross-loading.  These winds have been transporting snow and building slabs atop weak snow surfaces, forming soft slabs 1-2 feet deep on the leeward sides of ridges and slopes above 9,000’. These slabs will be most sensitive to the weight of a rider in very steep (>35°) and exposed starting zones. Look for signs of wind loading, including fresh drifts, textured surfaces, and features that may remain soft but appear dune-like and rippled. Areas seeing more wind may hold stiff, hollow-sounding features. The best approach is to "identify and avoid." 

    Small windslab at 8600' on an East aspect.

    Photo: Bridger-Teton Avalanche Center

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    Weak layers of snow are buried 2-4 feet deep in most mid and upper-elevation locations. The likelihood of triggering an avalanche involving these weak layers slowly decreases, yet remains possible today in very steep terrain. Slopes on the north half of the compass are most suspect. A large natural avalanche involving these layers occurred on 1/7, a good reminder of weak snow lurking below. Extra caution is needed around rocky, wind-affected, and unsupported slopes as they are where a human is most likely to impact the weak layers buried below.

    It is important to increase your margin of safety, given the uncertainty and high consequences associated with triggering a persistent slab avalanche. Traveling one at a time, stopping in islands of safety, and avoiding steep gullies or cliffs are all ways to increase your margins while traveling around avalanche terrain. However, riding terrain that is under 30° with no significant overhead hazard remains the best way to avoid this problem.

    (1/7/2025)

    Large persistent slab avalanche from earlier this week in the Snake River Range.

Avalanche Discussion

The knowns:

  • Around a foot of new snow has fallen over the past 72 hours. 
  • Wind-effected snow was observed in the range yesterday & some lower-elevation loose avalanches in the canyon due to sunshine. 
  • Numerous large natural avalanches were reported here last week.

The unknowns:

  • How well is the new snow bonding to the old snow surfaces?
  • Will additional observations of avalanche activity show more slides that broke deeper in the snowpack or reveal new surface snow instability patterns to watch out for?
  • Where is weaker snow near the base of the snowpack still a concern? Where is it less of a concern?

A few days of high pressure will equal more time to observe how new snow is setting up in the Snake. Until more time has passed and we can see how deeper layers handle new snowfall, I'm exercising caution and patience concerning the two avalanche problems above. Where these problems overlap is also where it is most likely to trigger a large, dangerous avalanche. Until the list of "knowns" is longer than the "unknowns," keep tight margins on the terrain you choose to enter, not only with regard to slope steepness but the shape of that terrain and the depth/structure of snow held on its slopes.  

Please consider submitting an observation HERE. Observations allow everyone to gain a better and more complete understanding of conditions. Thank you to everyone who has submitted observations this season!

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