Bollettino valanghe

Gunnison

Crested Butte Avalanche Center
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Pericolo valanghe

Wed
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Heightened avalanche conditions exist for the threat of human triggering hard slabs or loose snow avalanches. The most recent human triggered slab avalanches were reported on Saturday and are summed up in this video. In previously wind-loaded terrain, primarily at near treeline elevations, slab avalanches can break unpredictably above you and may be large enough to bury you. In other areas where snow surface is soft and sugary, like protected northerly terrain, human triggered loose dry avalanches continue to be reported daily.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Strong northwesterly winds last week raked the mountains and mixed into typically more sheltered locations.  The incremental wind drifting built hard slabs ranging from just a few inches to several feet thick.  Although you can find these slabs at any elevation, we've seen the most significant wind loading and slab formation occurring nearing treeline, especially in terrain with large fetches favored by northwest winds.   These slabs are slower to heal because they formed above exceptionally weak facet layers.  They can also be remotely triggered from below or adjacent to steep slopes where the drifted snow spans onto lower slope angles.   The problem is localized to leeward terrain features and most often appears on the surface as smooth, dense, lens-shaped deposits behind tree fences, on the lee sides of ridged terrain features, and in concave catchments such as gullies.   Collapses and shooting cracks are clear warning signs of the problem.  Give wind-loaded terrain a wider berth than normal: there have been several near misses this week with some slides breaking into lower-than-usual slope angles.

  • Loose Dry

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    Dry loose avalanches (sluffs) are a concern in wind-sheltered terrain on the north half of the compass.  Where the snow surface is weak and cohesionless, you can easily trigger sluffs that entrain the top 6" to 10" of loose snow on slopes steeper than 35 degrees. Ski cuts, moving across the fall-line while descending, or choosing lower-angled slopes are effective techniques to manage this problem. These point-release avalanches will accumulate more mass in long-running, steep terrain. Use caution above gullies where an avalanche can pile more deeply and above trees and cliffs where the consequences of getting caught in a small sluff will be magnified. This problem is most common in sheltered terrain below treeline, but you can also trigger sluffs on some near treeline slopes and a few above treeline slopes.     

Avalanche Discussion

We have now gone a couple of days without a fresh report of a human-triggered slab avalanche, however little has really changed in big picture conditions. The main wind-loading that created the current persistent slab avalanche problem occurred a week ago and was first highlighted by this "sleeper winds" observation. At the time, the alpine was already windblown so we didn't see much snow blowing off the peaks. It was the lower elevation bands that had snow available for transport and were then seeing winds mix into those lower elevations. Over the following days, the wind continued to mix into those lower elevations and sneakily build slabs over the weak old snow. By the end of the week, we started observing surprise human-triggered avalanches. Maybe we have recently seen a break in triggered slab avalanches because the problem is now understood and we all have adjusted our travel, or maybe the problem is getting older and more stubborn to trigger. Either way, this wind-loaded avalanche problem was labeled under the persistent slab header as it is expected to remain problematic and potentially continue producing surprise avalanches. 

The next storm seems to continue the donut hole theme for our forecast area, with better accumulations adding up to our north, our east, and our south, but not necessarily our forecast area. Ooo joy. Though we still have snow in the forecast and can expect changing avalanche conditions with the arrival of that snow. 

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