Bulletin d’avalanche

Northwest Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

Sat
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

Our snowpack is adjusting to the recent loading event which brought over 2 feet of snow to the favored areas. Warmer temperatures today will keep the likelihood of triggering a potentially un-survivable avalanche in play. Slopes with recent drifting and steep, southerly-facing slopes will be the most dangerous.  A smaller avalanche in recent snow may break into deeper weak layers buried at the bottom of the snowpack. Seek out areas with depths greater than 150 cm(5 feet) that are protected from the wind or slopes that are less than 35 degrees to minimalize exposure. 

 

 

Problèmes avalancheux

  • Persistent Slabs

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

    Slabs ranging from 5 to 8+ feet thick have formed around the compass and at all elevations over faceted weak layers in the lower snowpack.  The poor snowpack structure may be more sensitive in the wake of the most recent storm.  In the Northwest Mountains, the problem has become difficult to trigger because weak layers are deeply buried and hard to impact.  You are most likely to trigger an avalanche from a shallow area in the terrain, such as a rock band or where winds have 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 last week.  This avalanche would be hard to survive.

  • Wind Slabs

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

    Over two feet of fresh snow has been heavily transported by winds that shifted from southwest to northwest yesterday.  Large slabs up to several feet thick have formed below ridges and cornices, in cross-drifted gullies, and below abrupt rollovers.   Avoid steep terrain with signs of recent or active wind drifting.  

    1/12:  This large wind slab failed on Mt. Emmons sometime in the past 24 hours.  

Avalanche Discussion

Over the last 3 weeks, our snowpack has grown significantly and is becoming stronger. It has doubled in size since just before Christmas and weak layers are getting deeper and deeper.  This is Colorado however and we still have weaker snow resting at the bottom of the snowpack.  We have seen fireworks, in the form of large to very large avalanches, after each cycle of stormy weather during the recent weeks. The skies cleared yesterday, offering great views of the surrounding terrain after the snow and winds Tuesday and Wednesday. While we saw a few avalanches breaking deeper on generally shallower slopes, the vast majority of slides in the snowbelt were smaller and confined to the recent snow on drifted slopes. 

This pattern of activity supports the recent travel advice, which varies depending on overall snowpack depths. This video demonstrates some of those differences. While avalanche size will be larger, you are less likely to impact weak layers on slopes with depths greater than 150 cm or 5 feet. Areas near and East of town have slabs generally 2-4 feet thick as Eric observed in this ob from Cement Creek. As you move West and North of town, slab size grows to 5-8+ feet as the Zach's found near Pittsburg recently.  Regardless of what zone you are in, being keenly aware of snow depth is paramount. This is a great time to pop that probe out and verify that as you are moving through terrain. If you are stepping out, choose slopes with uniform depths devoid of rocks, trees, cliff bands and convexities where the snow will be thinner. A solid plan with your partners is also very important. Regrouping areas well clear of the path and runout will likely bring you out of visual and verbal communication.  Make sure to bring that radio and/or discuss safe zones in the event that the entire slope slides. 

Temps today will climb above freezing in many areas with off-and-on sunshine. As surfaces heat up, we will see the possibility of isolated, wet loose activity.  Avalanches in the surface snow are expected to remain relatively small, however, once in motion, they can trigger a much larger avalanche that breaks deeper in the snowpack.  There is always some uncertainty on the extent and effects of heating, don't be surprised if we see a large natural avalanche or two today.  Avoiding slopes with those tell-tale signs like rollerballs, pin-wheeling and point releases will reduce the hazard. In addition, be aware of drifted terrain at upper elevations for the possibility of lingering wind slabs. 

 

 

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