Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 3 years ago.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

Highlights

Avalanche danger will increase throughout the day as another round of snow arrives. Human triggered avalanches will become likely in the new snow at upper elevations. 

Look for cracking around your skis or snowmobile, and use test slopes to look for fresh slabs in the new snow. If you find these, step back to slopes under 30 degrees. 

Avalanche danger is considerable in the southern Bitterroot, where new snow totals are expected to be greatest today. As you move north through the Bitterroot range, avalanche danger will be moderate, especially around Lolo Pass.

Avalanche problems

  • Storm Slabs

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

    Sensitive storm slabs are likely today at mid and upper elevations. 6-8 inches of new snow today is expected to fall in the southern Bitterroot as another round of moisture arrives mid-day today. Further north, new snow totals will be less, with 3-5 inches expected. This will fall on 3-6 inches of snow from the past few days. 

    Human triggered avalanches are likely, and natural avalanches are possible. It will be possible to remotely trigger a storm slab during peak sensitivity times. 

    Expect storm slabs 6-12 inches deep, with isolated deeper slabs at upper elevation and leeward terrain. Test slopes are an excellent tool for identifying potential storm slab problems.  Shooting cracks and recent avalanches are red flags that you will likely trigger an avalanche on larger slopes. 

    Storm slab sensitivity is usually short lived. You can reduce risk by waiting a day before moving into avalanche terrain.

    (2/13/2024)

    Fresh storm slab in the Rattlesnake

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1.5–2.5

    Triggering a large persistent slab avalanche at upper elevation is a low likelihood, high-consequence scenario. It has been two weeks since the last avalanche on these layers, but the poor snowpack structure remains. 

    Dealing with this problem is an individual risk tolerance question right now.  Use slope angle if you want to avoid the problem completely. Large persistent slab avalanches are even more unlikely on slope angles 30 degrees or under.

Avalanche Discussion

Since our last forecast on the 11th, several small pulses of moisture delivered 3-6 inches of snow across the Bitterroot range. Today, snow is expected to continue, with another pulse of moisture arriving this afternoon. New snow totals are expected to be highest in the southern Bitterroot, especially around Lost Trail Pass, and decrease as you move north. Winds in the Bitterroot have been light and were sheltered overnight from the stronger east winds impacting the Rattlesnake and Sapphire ranges. 

This new snow is not falling on a significantly weak layer in the top portion of the snowpack and is expected to bond well with the old snow. Storm slab is the primary problem in the Bitterroot today. The good news about storm slab is that although it can be touchy and create an active avalanche cycle during the storm, it moderates quickly, and if you wait a day or two, the problem often goes away. 

What about the persistent slab problem? Why is it still on the forecast if it is unlikely? Even though we have not seen an avalanche on these deeper facets in two weeks, we are still uncomfortable with the poor snowpack structure and the potential for a large avalanche to surprise someone. How much you are willing to expose yourself to this problem is a matter of personal risk tolerance. Be aware that any avalanche triggered near the ground will be large and potentially catastrophic. 

Let us know what you are seeing by submitting an observation.

Ski and ride safe.

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