Bulletin d’avalanche

Northwest Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

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

Points saillants

5 inches of snow has fallen this morning with the potential for up to 12 inches by sunset.  Westerly winds are blowing at efficient speeds to drift the new snow to leeward terrain features.  Triggered avalanches may become likely today on drifted terrain.  Most avalanche activity will involve only the storm snow, but some well-drifted slopes, or terrain with a very shallow snowpack, could break deep and wide, creating a destructive avalanche.  Conservative terrain selection and cautious route finding are recommended.  Remain skeptical of drifted terrain during this loading period.  

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3.5

    Slabs ranging from 3 to 6+ feet thick have formed around the compass and at all elevations over faceted weak layers in the lower snowpack.  The poor snowpack structure produced widespread activity during stormy weather in early January.  Now the problem is becoming more difficult to trigger because the snowpack is adjusting and weak layers are hard to impact.  You are most likely to trigger an avalanche from a shallow area on the slopes, such as a rock band or where wind drifting has formed variable snow depths.  Give yourself a wide margin for error given how consequential the problem is right now.    Persistent slab avalanches can propagate widely through the terrain, or be remotely triggered from low-angle slopes connected to steeper slopes.  You can reduce your risk by traveling on slopes with a deep, uniform snowpack, and you can reliably avoid the problem by traveling on slope angles that are consistently less than 30 degrees.  

    1/4:  A destructive natural avalanche in Red Lady Bowl broke full width on Wednesday.  This avalanche would be hard to survive.

  • Wind Slabs

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

    Up to a foot of new snow will fall today accompanied by efficient westerly winds.  Fresh drifts are most likely to form on the east half of the compass.  Cracking in the new snow in open areas is a good sign that avalanches in the storm snow are becoming likely.  Use caution around drifted terrain features.  Most avalanches in the storm snow are expected to remain smaller in size but some slopes could produce a large avalanche.

    This avalanche on Mount Emmons failed about a week ago from a bout of wind drifting.  Expect similar potential today if the snowfall forecast verifies. 

Avalanche Discussion

Another storm has arrived and is set to deliver up to a foot of new snow and an inch of snow water equivalent by this evening.  This load will burden weak layers in the snowpack, particularly for terrain with shallower snow depths. The avalanche danger will increase throughout the day as snowfall accumulates and westerly winds load leeward terrain.

The Southeast Mountains have a generally shallower snowpack with more pronounced weak layers and thinner slabs.  On Sunday, CBAC forecast staff traveled around Double Top Mountain and experienced numerous signs of instability like cracking and collapsing and a very recent Persistent Slab avalanche.  On Saturday night, or Sunday morning a very large natural avalanche ran off Gothic Mountain well after the previous storm ended.  This evidence clearly suggests that deep-breaking natural avalanches are a real threat in drifted terrain and that human-triggered avalanches in sheltered areas remain likely for locations with a shallower snowpack.

The Northwest Mountains will tolerate the new load better, but concern remains for isolated drifted terrain to break deeply as snow and wind loads leeward terrain features.  Even though the concern for a deep and wide avalanche is less in the Northwest Mountains, freshly forming Wind Slabs are expected to be sensitive to the weight of a person.  Avalanches in the new snow could grow large enough to bury a person.  If you are considering entering avalanche terrain you will need to do so with caution and with solid evidence and reasoning.  If you find yourself in doubt, defer to low-angle terrain.

On Saturday, two snowmobilers were buried and killed in an avalanche near Winter Park.  Yet another tragic accident that brings the fatality count in Colorado up to four in recent weeks.  This is a sad reminder that our snowpack continues to catch people by surprise this winter.  

 

Régions couvertes