Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Out of date — this forecast expired 7 months ago. You’re viewing past conditions, not the current bulletin.

Highlights

Triggering a wind slab avalanche is possible anywhere the new snow has been blown into drifts. Wet avalanches will become possible on solar slopes if the sun comes out. Watch for signs of instability such as recent avalanches, shooting cracks, and wet snow deeper than six inches. If you see these, stick to slopes less than 30 degrees.

At Lolo Pass, wet loose avalanches will be the first avalanche problem.

Persistent slab avalanches are possible in the southern Bitterroot and unlikely in the rest of the zone. See the problem description below for more details. 

Avalanche problems

  • Wind Slabs

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

    In the past five days Lolo Pass and Twin Lakes have received about 35 inches of snow (3.5 – 4 inches of water) and Lost Trail has received 12 inches (1.4 inches of water). This snowfall was accompanied by moderate westerly winds. This is the ideal recipe for building wind slabs on easterly slopes.

    Skiers triggered wind slab avalanches in both the Bitterroot and Rattlesnake yesterday. Crowns were up to a foot deep in spots. Clear weather allowed us to see many natural avalanches that had happened earlier in the week. Click here to see the observations page for details.

    Moderate winds at ridge top will have formed new wind slabs overnight and will continue building them today. Additionally, triggering deeper wind slabs from the past few days is still possible.

    Identify wind slabs by looking for pillow-shaped deposits and wind drifts. They are most likely to form just below ridgelines, below roll-overs, and in cross-loaded gullies. Avoid slopes over 30 degrees where you see signs of wind loading.

  • Loose Wet

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

    In the Lolo Pass area, this will be the most important avalanche problem.

    If the sun comes out today, human-triggered wet avalanches will be possible on solar slopes. With warming temperatures and low-density surface snow, it will take very little solar input for new snow to become wet.

    If you find yourself sinking into wet surface snow or see roller balls, stay off of steep southerly slopes and away from their immediate run outs. Even small wet loose avalanches can have serious consequences.

    Pay attention to the weather and snow as you move through the mountains today. Winds and clouds may temper the sun's influence, but high temperatures will exacerbate it. Even though it's only January, wet snow should be on your mind.

  • Persistent Slabs

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

    The southern Bitterroot has a crust over facets buried just over a foot down. This weak layer is most prevalent at high elevations between 7000 and 8000 feet. In the northern Bitterroot, where we’ve received more snow, this same crust is much deeper and is not overlying an obvious facet layer. With this snowpack difference we only expect this persistent weak layer to be a problem in the southern part of this range.

    At high elevations we’ve found small facets buried just over a foot deep. This layer will be less than a foot deep in the Southern Bitterroot where there’s been less snow. These facets formed on the snow surface in late December and early January before getting buried. We have no reports of avalanches on this layer, but we’ve gotten propagation on it in snowpack tests.

    On solar aspects the sun likely destroyed the facets before they were buried. So, look for this weak layer on high elevation shady slopes.

    Regardless of the weak layer, you are unlikely to see obvious signs of instability, like cracking or collapsing, before triggering a persistent slab avalanche. Dig down and look for weak layers before committing to a line. Strong over weak snowpack structure or propagating extended column tests indicate you should avoid slopes over 30 degrees.

    (1/9/2026)

    Snowpit on a northeast aspect at 7600 ft in the northern Bitterroot

    Photo: Arden Feldman

Avalanche Discussion

Snowfall has come to an end, and we’ve moved into a period of high pressure. However, wind overnight may have built new wind slabs on top of old wind slabs, and a few buried weak layers still have our attention. Plus, warm temperatures today could create wet snow problems.

Low-density snow can warm quickly. Any slopes exposed to above-freezing temperatures and direct sun will become wet quickly. If an inversion develops, warming will be exacerbated at high elevations. Pay attention to changing weather, and don’t let wet snow surprise you.

With limited observations, uncertainty exists regarding the near surface facets buried about a foot deep. They formed during the New Year’s dry spell, and are likely only preserved where the snow remained cold. We haven’t seen avalanches on this layer, however visibility has been limited. Up near Whitefish, a skier triggered an avalanche on what appears to be the same layer. Click here for details. 

The weak layer in the Southern Bitterroot is associated with a crust buried on December 26th, with underlying facets. While this crust exists in the rest of our forecast area, we haven’t found facets underneath it anywhere else. The facets below the crust are the reason we remain concerned about this layer in Lost Trail area. We’ve continued to see propagation on this layer where facets exist under the crust.

If you see any avalanches, please let us know about them. If you dig in the snow, please let us know what you find. Tests are helpful but not necessary, even a photo of your snow pit wall is useful. Your information helps us reduce uncertainty, which leads to a higher accuracy forecast.

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