Bulletin d’avalanche

Bitterroot

West Central Montana Avalanche Center
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Danger d’avalanche

Sun
Alpin
2 · Modéré
Limite forestière
1 · Faible
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 3 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Skiers and riders could trigger a persistent slab avalanche at upper elevations on southern aspects. If you experience collapsing cracking, stick to terrain under 30 degrees. 

Natural and human triggered wet loose avalanches are possible if the clouds break today.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    There are multiple buried crusts with weak snow above and below in the Bitterroot. The slab above these crusts ranges from 6 inches up to a few feet thick. Avalanches are most likely on the crust that formed Tuesday when cold new snow fell onto wet snow, forming a thin layer of facets on the top of a stout, 3-5 inch crust. 

    You are most likely to encounter these buried persistent weak layers on south aspects in areas with previously buried sun crusts. Dig in the snow, and if you find crusts, be suspicious of weak snow and increased avalanche potential.

    If you experience collapsing or whumfing, stick to terrain under 30 degrees. 

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    Above freezing temperatures, no wind, and Spring sun create ideal conditions for wet snow avalanche activity. The partial cloud cover today should work to mitigate these conditions. In areas with a large break in the cloud cover, wet loose avalanches are possible on sunny aspects. 

    Most areas have a surface melt-freeze crust from yesterday's sun, and it will take time for this crust to break down, pushing any avalanche activity to later in the day. 

    Rollerballs and point releases are indicators that the snow is losing strength, and wet snow avalanches are likely to follow. Avoidance is the best management strategy for wet snow avalanches.

Avalanche Discussion

Today will be another beautiful day in the mountains with warm temperatures and minimal wind. Great skiing and riding conditions exist on northern aspects and in areas that have not gotten direct sun.  

Avalanche danger is focused on southern aspects today. Buried crusts and facets create a poor snowpack structure. Facets around crusts are a troublesome persistent weak layer because sensitivity and propagation are inconsistent, even on the same weak layer. When the slab fails above the crust, it has a firm and smooth bed surface to run on, creating far and fast running avalanches. 

One large D3 avalanche was observed yesterday on an upper elevation northeast aspect just outside of the forecast zone in the southern Bitterroot. The estimated size is 3-5 feet deep and 400 feet wide, likely running on a deeply buried crust/facet combination from a mid winter rain event.  Even at low or moderate danger, there is always the possibility that with the right trigger, large avalanches can occur.

Digging a snowpit is the best way to identify persistent weak layers. If you find them in your pit, there is a good chance that they exist in similar terrain. Remember, just because you don’t find weak snow or propagation in a snowpit does not mean that it doesn’t exist just a few yards away. Snowpits are an essential tool when looking for weak layers, but they can give a false sense of security if done incorrectly. 

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

Ski and ride safe. 

Régions couvertes