Avalanche forecast

Rattlesnake

West Central Montana Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 6 months ago. You’re viewing past conditions, not the current bulletin.

Highlights

Human triggered avalanches in the new snow will be likely by this afternoon and larger persistent slab avalanches are possible all day. Small avalanches have potential to step down and trigger a larger avalanche as well. 

Shooting cracks, collapsing, or fresh avalanches are all indicators of instability but you may not see any red flags or warning signs before triggering a larger persistent slab avalanche. 

If you want to avoid avalanches, stick to slopes less than 30 degrees in slope angle. 

Avalanche problems

  • Persistent Slabs

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

    A 1-2 foot slab of snow is sitting on top of persistent weak layers of surface hoar and near surface facets that formed during January.  The strain on this weak layer will be increased today as more snow falls on it. While there has been a decrease in activity on this layer the past few days, this could change and the problem could reactivate with the new load. Upper elevation north facing terrain is most suspect, especially in areas with a stiffer slab from wind loading.  

    Identify buried surface hoar by digging in the snowpack and looking for a thin grey line 1-3 feet below the snow surface. If you find this, be especially cautious as surface hoar avalanches can fail on low slope angles down to 30 degrees. A common trap with surface hoar is to dig high in start zones and not find it, then descend partway down the slope and trigger an avalanche on buried surface hoar. It can get destroyed high on slopes but preserved lower on the slope, creating tricky conditions for slope level snowpack assessment. If you dig a pit high on the slope and do not find buried surface hoar, do not trust that there is no buried surface hoar lower on the slope. 

    To identify buried near surface facets, look for a layer of weak sugary crystals below the most recent snow. If you find this hardness step off, avalanches are possible and terrain management with slope angle is the way to avoid avalanches. 

    Most of the surface hoar and near surface facets on south facing slopes were destroyed during periods of strong sun. Some south facing slopes still have buried crust/facet layers that are less reactive, but still pose a risk of avalanches. 

    With all persistent slab avalanches, it is possible to trigger them remotely from above, below, or to the side. You may not see any red flags or warning signs before triggering an avalanche on these layers.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–1.5

    4-8 inches of new snow today and 1-3 inches last night will be readily available for transport by ridgetop winds today. Expect fresh wind slab formation at upper elevation and along ridgelines. Any wind slab triggered has  potential to step down and trigger a larger persistent slab avalanche. 

    Be suspect of anywhere you find 6 inches or more of windblown snow. Wind slabs can be identified by their smooth or pillow like appearance, hollow feel, or by red flags like shooting cracks and fresh avalanches. If you find any of these and want to avoid wind slabs, use slope angle and stick to slopes less than 30 degrees in slope angle. 

Avalanche Discussion

A welcome increase in forecasted snow totals for today will bring a refresh to skiing and riding conditions. It will also increase strain on buried weak layers and potentially re awaken an avalanche cycle. 

Current weak layers are showing a high degree of spatial variability. What does that mean? It means that even on the same slope, things like the type of weak layer or slab thickness change. As we move from slope to slope, these things change even more. In conditions like this, careful route finding and slope assessment is critical. Use the forecast as a starting point but make an assessment of the slope you plan to ski or ride. 

Things like tracks on a slope are not indicators of stability. It will be possible for the 2nd or 5th person on a slope to trigger an avalanche. 

Glide cracks are opening up throughout all zones. Glide cracks are very unpredictable and can fail minutes after the crack opens or months after. Avoid spending time under open glide cracks. Cornices have the potential to break off naturally during periods of warming. Minimize the time you spend underneath overhung cornice on warm days. 

Avalanche education is a lifelong journey built on developing sound judgment, gaining experience, and applying repeatable decision-making systems in the backcountry. Our American Avalanche Association (A3) recognized Level 1, Rescue, and Level 2 courses are offered throughout the winter and help you travel smarter in avalanche terrain. Explore current courses and registration on the Education page. 

Please continue to submit observations, and ski and ride safe!

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