Avalanche forecast

Gunnison

Crested Butte Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Loose dry avalanches, or sluffs, have become the most commonly encountered avalanche problem by backcountry riders this week. While typically small, they can gain mass on larger terrain features and push you into more hazardous areas. The larger persistent slab problem remains a concern in wind-loaded terrain, though decreased snow quality often discourages riding there. The travel advice for some time has been to seek out softer, wind-protected snow in sheltered terrain to lower your chance of triggering a large slab avalanche, but you must be ready to manage the potential loose dry avalanches if you are riding on steep northerly facing slopes. 

Avalanche problems

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–1.5

    You can easily trigger gouging  "facet sluffs" on some very steep (~40° ) slopes that are protected from the sun and wind.  You're most likely to encounter the problem in start zones that have avalanched multiple times this season and have an unusually shallow and weak snowpack (<50 cm).  These avalanches release predictably and start small, but can grow to harmful sizes in long relief or if they push you into trees or gullies.  Use defensive or off-fall-line riding techniques to manage the problem, or move to lower slope angles to avoid the problem.  

    A debris pile from loose dry avalanches accumulating in a gully below the Climax Chutes. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    Slabs up to several feet thick are becoming increasingly isolated and difficult to trigger but remain a concern on some steep slopes facing west, north, east, or on wind-loaded southerly slopes.  You are unlikely to see signs of instability before triggering an avalanche that breaks on old weak layers.  Previously wind drifted terrain appears to be the most problematic, especially where slabs are thin near their margins, convexities, or rocky areas. You can reliably avoid the problem on slope angles less than 30 degrees without steeper slopes above you, and most wind-protected terrain lacks the problem.  

    This avalanche was triggered by a backcountry rider on 1/26 outside our forecast area near Ashcroft. This is a good illustration of an old slab having formed below the wind-loaded roll. Photo courtesy CAIC. 

Avalanche Discussion

A group was kind enough to share a report about getting caught off guard by their triggered loose dry avalanches yesterday. One member of the party was caught and swept off their feet. In Colorado, we are not as accustomed to dealing with loose dry avalanches or sluffs, because we are not riding in steep terrain during big storm cycles due to other avalanche problems. When the snowpack in our area develops this problem, it is because we are in drought conditions, and the snowpack is becoming so weak that it loses its strength and becomes cohesionless. Make a plan for managing this avalanche problem if you are riding in steep terrain, and expect these sluffs to continue growing in size as they run through consistently steep terrain. 

Slab avalanches are becoming tired, lethargic, and more difficult to trigger, but by no means have they been put to bed. All of the slab activity last week was in wind-affected terrain. These occurred following a strong westerly to northerly wind event that occurred between January 17th and January 23rd. As these slabs continue to age, weak layers will slowly adjust to their load, but given the persistent grains in those weak layers, we are not close to moving beyond the thread of more persistent slab avalanche activity. These slabs may take multiple tracks on the slope to find the right trigger point, like somewhere that the slab thins, and the weight of a rider can more easily affect the buried weak layer. Another reason that we may have observed a downtrend in slab avalanche activity is that the most worrisome terrain for triggering a slab avalanche has stiffer, more wind-affected snow, which isn't all that attractive to ride.  Our forecast team was targeting slab concerns last weekend, resulting in a remotely triggered avalanche on a small drifted slope and finding several propagating test results on buried weak layers  (video from Mt. Emmons, video from Schuylkill Ridge). These results highlight the continued potential for human triggering, which likely requires hitting the wrong spot (probably a thin area) on the wrong slope (probably a previously drifted slope where slabs are stiffer). 

The distribution of persistent slabs is the most isolated at below treeline elevations, as slabs have often faceted away and are contributing to the loose dry avalanche problem. The few remaining slopes that could produce a slab avalanche will likely be previously cross-loaded by the wind event that mixed down to lower elevations early last week. 

 

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