Avalanche forecast

Rattlesnake

West Central Montana Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Highlights

Skiers and riders could still trigger very large persistent slab avalanches on upper elevation northerly slopes. Isolated and stubborn wind slabs could also be found at upper elevations. Carefully assess the snowpack before committing to upper elevation slopes steeper than 35 degrees. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–3

    Skiers and riders could trigger very large and dangerous persistent slab avalanches on northerly aspects at upper elevations. These slides could be up to 5 feet deep and break at the ground. Triggering one is unlikely, but not impossible - it’s a low likelihood, high consequence scenario. Choosing low-angle slopes under 35º, ideally under 30º, is the best way to manage these layers. If you step out onto steeper terrain, be sure to dig down and see what weak layers may be underneath you. Never ignore a poor snowpack structure, such as a weak layer buried under a slab. Avoid potential trigger spots where the snowpack is thin, like convex rolls and around rocks and windswept ridges. 

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1–2

    Skiers and riders could find isolated and stubborn wind slabs at upper elevations. They could be on all aspects due to shifting wind directions. Wind slabs are often found just below ridges and in cross loaded gullies. Wind slabs can be identified by their smooth and rounded appearance. Signs of instability like cracking warn you that dangerous conditions exist. Carefully assess the snowpack before committing to upper elevation slopes steeper than 35 degrees. 

Avalanche Discussion

The avalanche hazard remained fairly steady over the last several days. Observers reported stubborn wind slabs on east aspects yesterday due to previous west winds. This morning, winds are blowing moderately out of the southeast. There is limited snow available for transport, but there may be small new wind slabs on north and west aspects today as well. 

A couple of weak weather systems will impact us over the next few days. We can expect scattered snow showers only amounting to light accumulations, light southwest winds, and a gradual warming trend through the weekend. If you find more new snow than forecasted, be on the lookout for fresh avalanche problems, especially in wind loaded areas. 

Between December 25th-28th, a strong, warm storm brought heavy rain up to 8000 ft and significant snow. We now have a several-inch thick rain crust up to at least 7000 ft that makes it difficult to trigger any weak layer beneath it. The rain crust is thinner or nonexistent at upper elevations, so skiers and riders could still trigger failures in buried weak layers. The increase in snow depth from recent storms promoted rounding in the snowpack. Buried weak layers are healing and becoming less sensitive. However, the healing process takes time, and poor structure remains, especially on northerly aspects. In the Rattlesnake, weak basal facets and buried surface hoar are the primary layers of concern. If you find any of these layers where you plan to ride, avoiding steep slopes is the best strategy. 

In isolated areas with thinner crusts at middle elevations, it is still possible to impact weak layers buried below. Remember that Low danger does not mean avalanches are impossible. 

Low likelihood, high consequence problems like this are very difficult to manage. We don’t know exactly what it will take for a slope to fail and produce a dangerous avalanche. The weight of a skier or rider in the right trigger spot could be enough. If you are ever in doubt, take a step back to lower angle terrain. If you decide to ride steeper slopes, be sure to use good travel practices and ride one at a time. 

Observers reported open glide cracks on numerous slopes. Glide cracks can fail and avalanche unpredictably at any time. Avoid traveling on or below slopes with glide cracks. 

Public observations are a critical tool for us to produce accurate forecasts. Please help us out by submitting an observation. If you see any avalanches or experience collapses, we would love to hear about them! 

Ski and ride safe.

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