Boletín de aludes

Bitterroot

West Central Montana Avalanche Center
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Peligro de aludes

Sat
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 8 months ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Another round of fresh windslab development is expected today with continued ridgetop winds. It will be possible to trigger avalanches anywhere the snow has blown into slabs 6 inches thick or deeper. Fresh wind slabs may hide older wind slabs from the past 72 hours and could break deeper than expected if triggered. 

Watch for red flags like shooting cracks, blowing snow, or fresh avalanches. If you see these, stick to slopes less than 30 degrees.

Avalanche danger is Considerable in the central Bitterroot along the Bitterroot crest in areas like upper Lost Horse drainage

Low elevation (below 5500') at Lolo Pass will have moderate danger due to higher new snow totals and blowing snow. Low elevation danger for the rest of the Bitterroot range outside Lolo Pass is low danger. 

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. 

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    How much snow is available to be transported by the wind varies dramatically across the Bitterroot zone. With that, size and sensitivity of wind slabs will vary as well. Since the 5th, 24 inches of snow has fallen in the Central Bitterroot. At Lolo Pass, 21 inches of snow has fallen. In the south, new snow totals are much less at 6 inches for Saddle Mountain.

    Periods of stronger winds during this multi day snow event steadily built wind slabs on east aspects. The result of this is multiple layers of slab along ridgelines and crossloading in complex terrain. Expect the fresh wind slabs to be sensitive, and the older wind slabs to be more stubborn. 

    Wind slabs often form just below ridgelines, below slope convexities, and in cross-loaded gullies. Identify wind slabs by looking for pillow-shaped deposits and wind drifts.  Evaluate snow and terrain carefully as older wind slabs may be hidden by new snow. Avoid slopes over 30 degrees if you see signs of instability like recent avalanches, shooting cracks, or blowing snow. 

    (1/7/2026)

    A wind slab human triggered by cornice on an upper elevation east aspect

    Photo: Arden Feldman

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    1.5–2.5

    Triggering a larger slab avalanche that fails on small faceted crystals below the uppermost crust remains possible, especially in the southern Bitterroot. Elewhere in the zone, this problem is unlikely. 

    No avalanches have been observed on these layers in two weeks, but as it continues to snow, the load on these layers is increasing and may reach a tipping point. 

    In the southern Bitterroot, we have not seen recent avalanches on this layer, but snowpack structure is poor and shows propagation potential in snowpits. There is some uncertainty about the distribution of this problem, but yesterday WCMAC staff dug deeper into the problem and found it isolated to terrain between 7000' and 8000'. Below 7000', the crust is thicker and the faceting process did not occur as effectively around the crust. Above 8000', the crust is thin enough to not have facets form around it. 

    You are unlikely to see obvious signs of instability, like cracking or collapsing, before triggering a persistent slab avalanche. To identify areas where the problem exists, dig in the snow and look for weak snow surrounding crusts. If you find this and want to avoid the avalanche problem, stick to slopes less than 30 degrees in slope angle.

Avalanche Discussion

There is still uncertainty around the persistent slab problem and its distribution. It is unlikely in areas like Lolo Pass where December rain events fully saturated the snowpack. As you move south to areas like the central Bitterroot, it is unlikely in areas like Lost Horse or along the Bitterroot crest where the snowpack is deep. At the same elevation at the mouth of the Bitterroot canyons, the snowpack is much thinner and areas with weak snow around a crust are possible. If you decide to dig in the snow, please let us know what you are finding. Snowpit tests are helpful but not necessary, even a photo of your snowpit wall helps!

If you would like to learn more about the near surface faceting process than formed this layer, and why it is so specific in its distribution, check out this article from the Avalanche Review and focus on the melt-layer recrystallization process. 

On January 5th, a snowmobiler was killed in an avalanche near Lake Tahoe. Our condolences go out to the family and friends. If we look at the preliminary accident report, we find terrain and wind slab avalanche size that resembles much of the motorized terrain in our forecast zones. We mention this as a reminder and learning opportunity that even short running avalanche paths can be dangerous if they bring you into trees or terrain traps. 

Let us know what you see by submitting an observation. We appreciate all observations, no matter how small, as our forecast area is large, and it helps us understand conditions across all zones. 

Ski and ride safe!

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