Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
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Out of date — this forecast expired 6 months ago.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

Triggering a persistent slab avalanche will be possible today at mid and upper elevation anywhere a slab 1-2 feet deep sits on buried surface hoar or buried near surface facets. North facing terrain, areas shaded from the sun, and wind loaded slopes are most suspect.

Collapsing, whumfing, shooting cracks, and fresh avalanches are all indicators of instability, but you may not see any red flags or signs of instability before triggering an avalanche today. If you dig in the snow and identify a slab with weak snow below it, avoid avalanches by sticking 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.  Upper elevation north facing terrain is most suspect, especially in areas with a stiffer slab from wind loading.  We saw an active avalanche cycle on these layers earlier this week, and although triggering an avalanche on these layers is becoming more difficult, avalanches are still possible today. 

    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. These 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.

Avalanche Discussion

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. 

These layers are becoming less reactive at the moment. If we see a large increase in snow above them with additional storms, that could change and re awaken them. It will take time for these layers to fully heal. 

Looking forward, another few inches of snow is expected this weekend but is unlikely enough to create fresh wind slab problems or re awaken buried persistent weak layers. There was widespread surface hoar growth Wednesday - Friday this week. As this new snow comes in, pay attention to where the surface hoar is preserved and buried by fresh snow as this will become a future weak layer in the snowpack. 

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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