Bulletin d’avalanche

Northwest Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

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

Points saillants

Avalanche conditions continue to improve SLOWLY. However, troublesome snowpack structures exist, and you could trigger a dangerous avalanche on some slopes.  The variation in snowpack from one feature to another due to seasonal snowfall totals, wind, and previous avalanche activity creates a complex and difficult-to-predict scenario.  You can reduce your risk by selecting small, low-consequence terrain on suspect aspects or sticking to mellower slope angles.  Slab avalanche concerns are less pronounced on wind-sheltered southerly slopes, but warm temperatures may create a wet, loose avalanche problem.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–2.5

    Slabs averaging 2 to 3 feet thick in sheltered terrain and larger in wind-loaded terrain can be triggered where they formed over well-developed facets and collapsible crusts on west, north, and east aspects. Additionally, wind-loaded slabs could fail above buried crusts on high elevation, southerly aspects.  Relatively shallow slopes (<120cm)  and terrain features where slabs get thinner are most problematic.  Slab behavior is challenging with variable and deceptive feedback, remote triggering potential, and wide propagation across terrain features.  You can reliably avoid the problem on slope angles less than 30 degrees without steeper slopes above you, and most mid to low-elevation southerly aspects lack the problem.  

    This avalanche was explosively triggered 1/13 on the Irwin West Wall. The avalanche debris was 10 to 15 feet deep! Photo: Jake Hutchinson

  • Loose Wet

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

    Warming temperatures on Thursday may spur a round of Wet Loose avalanches on steep, sunny slopes.  Rocky areas may be more prone due to increased warmth.  Observers noted some natural avalanches on Wednesday, with activity expected to increase on Thursday as temperatures rise.  Natural releases are expected today.  Avalanche size is often small, but longer slopes may produce bigger slides.  There's an outside chance that a Wet Loose avalanche could release a much more dangerous slab avalanche as it descends.  Look for moist to wet surface snow and roller balls to clue you into the developing problem. 

Avalanche Discussion

Over the past few weeks, it was a long, slow trudge for the avalanche danger rating to drop to MODERATE.  The number of dangerous slopes has slowly decreased with time for various reasons.  Some slopes on the Persistent Slab distribution rose lack a slab due to wind erosion and the faceting process weakening the slab.  Other slopes lack a slab due to avalanche activity during the natural avalanche cycles of Thanksgiving and Christmas.  Some slopes have all the right ingredients for a dangerous human-triggered avalanche.  This observation from Carbon Peak documents multiple collapses and shooting cracks, and a very recent natural avalanche on WSC Peak clearly illustrates that the snowpack remains dangerous on some terrain.  A highly variable snowpack exists from one slope to another, creating complex decision-making.  Current conditions are a guessing game due to the variation across the landscape.  Unfortunately, some slopes could hurt or kill you if you guess wrong.  Choosing simple terrain with modest slope angles that are short with clean runouts can reduce the risk of being wrong.  A safer bet is to keep to lower-angled terrain, enjoy the nice riding conditions, and wait for avalanche conditions to improve sometime in the future.

The warming temperatures on Thursday may throw another wrench into an already tricky snowpack.  Temperatures at valley bottoms remain deceptively cool today, but once you climb above the cold sinks, expect to encounter temperatures in the 30s with light winds.  Overnight low temperatures at 12,000 feet are in the upper 20's, so confidence is high that snow surfaces will become wet on sunny terrain features.  Wet Loose avalanches present a bigger issue in the Northwest Mountains forecast zone due to more recent snowfall last weekend.  Lesser totals fell in the Southeast Mountains, so there is less snow for Wet Loose avalanches to gather.  Wet Loose avalanches are often easier to manage than Persistent Slabs as they behave more predictably.   However, if you encounter wet surface snow on an aspect/elevation highlighted by the Persistent Slab Rose, there is a chance a loose avalanche could step down and trigger a much more dangerous slab.  You'd be smart to avoid steep terrain where the two problems overlap.

Events:  Our next Fireside Chat is this Thursday, 7 p.m., at the Billy Barr Lounge, where Danielle Beamer will discuss Mental Health and Backcountry Decisions.  The event is free and open to all.  

Régions couvertes