Bulletin d’avalanche

Southeast Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

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

Points saillants

A few large natural avalanches on Whetstone ran Monday night from minor amounts of wind drifting.  Increasing winds today will sustain dangerous conditions on wind-loaded slopes.  We are still finding frequent and obvious signs of instability above 11,000' where recently formed slabs 1 to 2 feet thick sit precariously over a tricky surface hoar layer.  You can find safer riding on lower slope angles or at lower elevations where recent slabs are less reactive to triggers.    

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2.5

    A new round of weak layers was buried on February 2nd. These weak layers consist of widespread surface hoar and facets on most east, north, and west-facing slopes, and along with some faceted crusts on higher elevation southerly aspects. Slabs 1 to 2 feet thick over these weak layers are sensitive to skiers and riders. This avalanche problem can be remotely triggered from flat terrain, or may propagate further than expected.  Shooting cracks or collapses are a clear sign of danger, but these obvious signs of instability will not always show themselves before an avalanche releases.  There is also a lower likelihood potential to trigger older, larger slabs on weak layers deeper in the snowpack, most likely from shallow terrain features or step-down avalanches.  

     

    A recent skier triggered persistent slab on Coneys that likely failed on a layer of buried surface hoar.  

  • Wind Slabs

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

    Increasing westerly winds will be drifting snow into fresh drifts at higher elevations.  Look for blowing snow or stiff snow surfaces below leeward ridges or cross-loaded terrain to identify the problem.   Although most wind slabs today will be relatively small, they can be trouble in high consequence terrain or if they step down and trigger a larger persistent slab.  

    A recent wind slab on Mt Baldy.  Avalanches like this are a concern over the next few days.  

Avalanche Discussion

The bullseye for the most dangerous conditions is still pointing at the Southeast Mountains, where we continue to observe rumbling collapses and shooting cracks (Ex. West Brush, Emmons) over our troublesome surface hoar.  Monday night's natural avalanches on Whetstone highlight how even modest amounts of wind drifting can upset our persistent slab problem.  Wind drifting is expected to increase today and tomorrow, which will keep the threat of large natural avalanches ongoing near and above treeline near and east of our zone boundary.  In the Southeast Mountains, the most recent generation of persistent slabs is about a foot deep below treeline, and these thinner slabs are faceting away and becoming much less concerning now below about 10,500'.  

In the Northwest Mountains, slabs are thicker and more stubborn to human triggers at all elevations.  In the most favored areas near the Ruby Range, our February 2nd weak layers have been under a larger amount of stress for a longer period, which helps them gain some strength now, relative to the shallower parts of the forecast area.  Today's wind drifting is not as concerning for our persistent slab problem there, but we lifted the danger above treeline to account for fresh wind slabs and the isolated potential for large natural releases from our fickle weak layers.   Evan's notes on snow available for transport are relevant with today's strengthening west winds across our entire forecast area.   

In wind-sheltered terrain, it has been almost a week since the loading period ended and our surface hoar layers are becoming more difficult to trigger.  Moderate slope angles (mid 30's or less) have been significantly less problematic than steeper rollovers in the past week.  The accidents on Snodgrass and Anthracites (preliminary report now available) were both on slopes steeper than 40 degrees, and our forecasters have observed similar patterns while hunting for feedback this week.  You can significantly reduce your risk today by avoiding steep convexities and those very steep slope angles that have been most problematic.   Furthermore, consider terrain consequences: clean runouts free of trees and gullies are more survivable if you get surprised.  

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