Boletín de aludes

Bitterroot

West Central Montana Avalanche Center
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Peligro de aludes

Sat
Alta montaña
2 · Moderado
Límite del bosque
1 · Débil
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

Triggering an avalanche is possible in newly drifted snow at high elevations. Cracking, collapsing, recent avalanches, and extensive blowing snow are signs to avoid avalanche terrain.

Buried weak layers around crusts pose a low likelihood high-consequence persistent slab problem. You have to dig down and look for this layer, as you’re unlikely to see other signs of instability. If you find weak snow surrounding buried crusts, stick to slopes less than 30 degrees.

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–1.5

    Overnight the highest elevations saw a few inches of snow and light to moderate westerly winds. Small, fresh wind slabs are expected today at upper elevations. Human triggered avalanches are possible anywhere new snow has built slabs 6 inches thick or more.

    Identify wind slabs by looking for pillow-shaped deposits and obvious drifting. With westerly winds, you are most likely to find wind slabs today on northeast, east, and southeast aspects.

    Avoid slopes over 30 degrees if you see recent avalanches, extensive blowing snow, or experience cracking and/or collapsing in the new snow.

    Fresh wind slabs can hide older and deeper wind slabs from earlier this week. This old wind slab will feel like upside-down snow in the top foot of the snowpack, and will be found on immediate ridge crests. The same travel rules apply – if you find one of these old wind slabs, avoid wind loaded terrain over 30 degrees.

    In areas without wind loading, you are unlikely to find enough snow for a new snow avalanche.

    Cracking in a wind drift

     

  • Persistent Slabs

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

    This is a classic low-likelihood high-consequence avalanche problem.

    We have not seen recent persistent slab avalanches, but this layer has been reactive in snowpack tests. Triggering a persistent slab avalanche right now would require bad luck by finding a place where the weak layer is sensitive and the overlying slab is thin.

    The current storm is adding load to the snowpack. Any additional weight on the snowpack, no matter how small, could make buried weak layers more sensitive to triggering.

    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 snow surrounding crusts. If you find strong snow over weak snow, stay off of slopes over 30 degrees.

    Our main weak layer concern is sugary facets surrounding crusts that are buried two to four feet deep. This facet crust combination was formed by rain and fluctuating freezing levels in mid to late December.

    The highest elevation north-facing slopes have additional weak snow near the ground. This snow is gaining strength, but could be triggered in isolated areas by a very large load.

    (12/31/2025)

    Snowpit on a north aspect at 6800 ft in the Bitterroot

Avalanche Discussion

The most recent weather forecast has downgraded today’s snowfall amounts. This means we’ll only find enough snow for new snow avalanches in wind loaded areas. Look for signs of instability anywhere you see more than 6 inches of wind drifted snow. Obvious red flags such as cracking, collapsing, and recent avalanches are your cue to avoid avalanche terrain.

This new snow is adding load to a structurally weak snowpack. Each storm increases the weight of snow over existing weak layers and changes the structure of the overlying slab. Eventually increased load can lead to a period of persistent avalanche activity. Sometimes a series of small incremental loads can tip the balance. Each time it snows, it’s good to consciously remind yourself that these weak layers exist, and stick to slopes under 30 degrees during and immediately following storms.

As the temperature inversion moves out, we’re left with above-freezing temperatures at some mid-elevations. This means you are likely to find moist snow at our middle elevation band, even if low elevation snow remains frozen. Low elevation could see rain, but at many low elevation locations (specifically the Rattlesnake), there is not enough snow for avalanches.

If you find yourself sinking into wet or unsupportable snow, or seeing roller balls start to entrain mass, it’s time to get out of avalanche terrain.

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