Bulletin d’avalanche

Bitterroot

West Central Montana Avalanche Center
Voir sur la carte

Danger d’avalanche

Wed
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
Open full map
Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

It is possible to trigger an avalanche in the new snow that is large enough to bury, injure or kill a person. The hazard will increase throughout the day with continued snowfall. Wind affected areas are touchier. Avoid slopes over 33º, wind loaded slopes below ridgeline, and convexities.

Problèmes avalancheux

  • Storm Slabs

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

    Up to 12” of new snow in the past 72 hours sits on slick rain crust and faceted snow. An additional 4-8 inches arrives today and will increase the likelihood of storm slab. Cool temperatures have kept the snow light and mostly unconsolidated. However, the increased weight of the new snow may accelerate slab formation. Today, expect soft slabs that break predictably on steep convexities, and loose snow avalanches on steep slopes. 

    Where the snow has been wind affected expect touchier conditions and stiffer slabs. Multiple aspects are affected. Yesterday winds were loading east slopes. Today winds have shifted and are light with moderate gusts, capable of loading west and south slopes. 

    Sticking to slopes under 33º is a good idea today, and avoid wind loaded start zones below ridgeline.

     

  • Persistent Slabs

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

    On north slopes above 8000’ in the southern Bitterroot, reactive buried facets could fail with the weight of a skier or rider. These were 2 feet deep (62 cm) last Friday but are currently being buried deeper by new snow. South winds yesterday may have added to the loading. 

    The potential exists for storm slab or cornice fall to step down to this layer. Exercise extra caution in this zone. Avoid slopes over 33º.

Avalanche Discussion

Since the last forecast, up to 12” of snow has fallen, temperatures have been in the low 20s above 6000’, and winds have been moderate and westerly. 

Today, expect up to 8” of low density new snow. Winds have shifted to northeasterly and are light with moderate gusts. Temperatures will drop throughout the day, dipping below 0º tonight.

Last week's rain crust is getting buried deeper, improving skiing conditions, but it may be a problem layer for a while. Saturday saw a skiff of snow, and cold overnight temperatures promoted faceting, setting us up with a weak layer and slippery bed surface underneath the new snow. Temperatures are cool, and sun warming is minimal due to cloud cover. The new snow will be slow to consolidate into a slab, but continued snowfall today will increase the hazard. As the new snow consolidates into a stiffer slab over the next few days, we can expect more widespread reactivity and increasing slab sizes. Any wind will easily transport the low density snow creating wind slab. 

A local ski tourer recently relayed their experience of ski cutting a small windslab before skiing a slope and going for a short ride when the slab broke larger than he expected. He had successfully triggered a small slab that broke predictably on the slope the day before. Expecting the same, it broke larger and above him because it had stiffened over the intervening 24 hours. He luckily survived without injury. It’s a good, free lesson to choose safe test slopes, not make assumptions about windslab in the absence of red flags, and that avoidance of suspected windslab is often the best approach. 

Enjoy the new snow, but stay alert for changing conditions and red flags such as shooting cracks. Avoid wind loaded slopes, steep convexities, and terrain traps.

Please let us know what you are finding out there. You can submit observations here.

Ski and ride safe.

Régions couvertes