Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The avalanche warning has been terminated. However, ongoing snowfall and strong winds, combined with recent rain and rapidly changing temperatures, have created dangerous avalanche conditions today. Skiers and riders are likely to trigger large wind slabs on middle and upper elevation slopes. Very large persistent slab avalanches are possible today. Avoiding slopes over 30 degrees is the best way to manage the hazard. 

Avalanche problems

  • Wind Slabs

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

    4 to 10 inches of new snow and strong southwesterly winds have built wind slabs on leeward aspects. Today, another 3 to 6 inches of snow and up to 12 inches in the southern Missions combined with strong westerly winds will continue building these slabs. Skiers and riders are likely to trigger large wind slabs today. Upper elevation easterly aspects will have the largest and most sensitive slabs. 

    Wind slabs are often found just below ridges and in cross loaded gullies. However, the winds were likely strong enough last night to deposit slabs in unusual places well below ridgelines. Wind slabs can be identified by their smooth and rounded appearance. Signs of instability like cracking tell you that dangerous conditions exist. Wind slabs are most easily triggered on slopes steeper than 35 degrees. However, considering the possibility of a wind slab stepping down and triggering a much larger persistent slab avalanche, we recommend you avoid slopes steeper than 30 degrees today. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Multiple persistent weak layers throughout the snowpack and forecast area have been loaded by rain and snow and weakened by rapidly changing temperatures. Additional snow today will add to this load. Very large persistent slab avalanches, up to 5 feet deep and failing at the ground, are possible. Upper elevation northerly slopes are the most suspect. Avalanches could be triggered remotely from above, below, or the sides. You may not see red flags like cracking or collapsing, or unstable snowpit tests before an avalanche is triggered. Avoiding slopes steeper than 30 degrees is the best way to manage the hazard today. 

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Significant rain and warm temperatures over the last couple of days added a lot of liquid water to a previously cold, dry snowpack. Temperatures finally dropped below freezing last night at most elevations, but there is uncertainty about how solid the snowpack has refrozen. New snow from last night may insulate the old wet snow. Lingering wet snow may cause wet avalanche problems today. You will need to regularly assess the status of the refreeze in your travels today. If you find a stout crust, wet avalanches are unlikely. However, if you find unsupportable wet snow, you could still trigger a very large wet avalanche. Middle elevations are the most suspect for lingering wet avalanche problems today. 

Avalanche Discussion

A wild week of weather and dangerous avalanche conditions is slowly winding down, but it’s not over yet. Last week, we received up to 3 feet of snow and extremely cold temperatures. Then, over the weekend and into this week, we received significant rain up to at least 8000 ft and very warm temperatures. The snowpack never responds well to such rapid changes. Currently, the totals stand at 2.5 to 5.5 inches of precipitation in the last eight days, with another 0.25 to 0.5 inches (3-6” of snow) forecasted through tonight. The southern Missions are favored to receive up to 12 inches of snow by tomorrow morning. 

There is significant uncertainty in the forecast today due to a lack of recent observations and rapidly changing temperatures. With the rain and warm temperatures, yesterday was likely the day for natural avalanches, but predicting the tipping point for natural avalanches is difficult. They could occur today as well. Temperatures finally fell below freezing overnight. This may have frozen and locked up some slopes. However, today’s snow will only increase the load on the snowpack. We've been concerned about persistent weak layers deep in the snowpack for weeks. Recent avalanches, whumpfing, cracking, poor structure, and easy failures in stability tests all indicate that the snowpack is primed to fail. That hasn’t changed today. Very large persistent slab avalanches remain possible. Large wind slabs are likely. Considering the consequences of a very large avalanche and the high level of uncertainty, we recommend avoiding avalanche terrain today. Current conditions are dangerous and challenging. Don’t let your guard down. 

If you see evidence of recent avalanche activity, please let us know by submitting an observation. 

Ski and ride safe. 

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