Bulletin d’avalanche

Gunnison

Crested Butte Avalanche Center
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Danger d’avalanche

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

Points saillants

The threat of a dangerous slab avalanche lingers on some previously drifted terrain features.  Concerning slopes are more common near and above treeline on leeward features but may exist in isolated places below treeline.  You can reduce the risk of slab avalanches by traveling in wind-sheltered areas. However, you will likely trigger loose avalanches (sluffs) on steep slopes facing the compass's north half that are protected from the wind.  Don't underestimate the consequences of taking a ride in a loose avalanche, and if you'd rather not manage the problem, avoid it on slope angles less than 35 degrees.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    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 the wind forming a slab below a midslope roll. 

    Photo courtesy CAIC. 

  • Loose Dry

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    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. 

Avalanche Discussion

Slab avalanche concerns have greatly eased over the past few weeks, largely due to a lack of recent snowfall.  However, several windy periods over the past two weeks have kept the threat alive on drifted terrain.  Upper-elevation terrain (near and above treeline) is the most likely place to encounter stiff slabs above persistent weak layers.  As time increases since slabs formed, they have become more difficult to trigger and are unlikely to produce signs of instability before an avalanche releases.  Some slopes may see multiple riders before someone finds the wrong spot on the slope and releases a large slab.  Thinner spots in the slab are the most likely place on a slope to impact weak layers, but it can be difficult to see or predict where trigger points exist.   Continue to use caution when you encounter cohesive slabs in the snowpack, and consider the consequences of releasing a large avalanche.  The likelihood of triggering a large slab avalanche has decreased over the past few weeks, but the consequences remain serious on previously drifted slopes.  These observations from the past week may shed more light on the problem (Mount Emmons, Schuylkill Ridge,  Upper Cement/Brush Creek) and how it may appear in the terrain.

In wind-sheltered areas you are more likely to encounter the Dry Loose avalanche problem as the past few weeks of cold and dry weather have weakened the snowpack significantly.  On Tuesday, a group shared an observation of being caught off guard by the gouging nature of loose avalanches on Schuylkill Ridge.  Don't underestimate the power of small loose avalanches and the potential consequences of being carried into rocks, trees, or gulleys.  Anticipate loose avalanches and make a plan to manage them in steep terrain.

Although the snowpack is commonly faceted and weak in sheltered areas, recent winds formed slabs in isolated places below treeline.  These observations from Pittsburg and above the East River illustrate that you could encounter a sensitive slab at lower elevations where winds can transport snow.  Keep your guard up as you travel through open areas down low and steer around stiff, smooth-looking deposits.

Régions couvertes