Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

West to northwest winds transported a significant amount of snow onto lee terrain over the last 24 hours. These wind slabs were reactive yesterday and will become more stubborn today. A triggered wind slab could be several feet deep and produce a surprisingly large avalanche. Consider routes that avoid or limit your exposure to wind-loaded terrain. In wind-sheltered areas, loose snow avalanches are common on steep slopes, but keep an eye out for open areas where the wind may have created wind slabs in unusual locations. Slab avalanches breaking deeply into the snowpack remain a lower probability, but high consequence avalanche problem.  

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    In the last 24 hours, West to northwest winds has averaged in the teens to the twenties, with strong gusts in the thirties and forties at 12,000ft. These winds were also transporting snow in some open valleys and below treeline locations. Significant snow transport was observed on Wednesday. These wind slabs will become more stubborn to triggering today, but a triggered avalanche will easily be big enough to bury a human. Larger terrain could even produce a destructive avalanche. This avalanche problem is most commonly located on the lee sides of ridgelines and cross-loaded terrain features. They can also be found in more isolated locations at below treeline elevations. 

    A large wind slab that released in Red Coon Bowl earlier this month. 

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3.5

    Slabs ranging from 5 to 8+ feet thick are resting over faceted weak layers in the lower snowpack around much of the compass. These weak layers have generally adjusted to their current load and become difficult to trigger. The most suspect areas to release this avalanche problem would be in recently wind-loaded terrain and from trigger points or areas where the snowpack thins to a below-average depth. Such as near rock bands, on some slopes that previously avalanched and have refilled, or where winds have formed variable snow depths. Persistent slab avalanches can propagate widely through the terrain, or be remotely triggered from low-angle slopes connected to steeper slopes. You can reduce your risk by traveling on slopes with a deep, uniform snowpack, and you can reliably avoid the problem by traveling on slope angles that are consistently less than 30 degrees and not connected to steeper terrain above.  

     

     

    1/4:  A destructive natural avalanche in Red Lady Bowl broke full-width last week.  This avalanche would be hard to survive.

Avalanche Discussion

The avalanche danger is slowly decreasing from yesterday as wind speeds are expected to become light and stop transporting snow today. CONSIDERABLE avalanche danger remains at above treeline elevations as wind-loading will hold on the longest at those elevations and the potential avalanche size will be the greatest. A triggered wind slab on a big alpine feature could no doubt be deadly and/or produce a destructive avalanche. In general, wind slabs are expected to be stiff and have become stubborn to trigger. Obvious signs of instability may be limited. These slabs will most commonly fail on density changes in the upper snowpack or thin crusts that formed in between the recent storms on southerly-facing slopes. 

The persistent slab avalanche problem is also seeing a decreasing likelihood. In the southeast mountain forecast, this problem is now labeled as "possible". There are more areas in the SE mountains where slabs are thinner and easier for the weight of a human to affect the weak layer below, but even these thinner snowpack areas have had time to adjust to their current load and become less reactive. This avalanche problem will not give any obvious warning signs, and it could take many people riding or skiing a slope before, perhaps, someone finds the right trigger point. The NW mountains have a commonly deep snowpack. Something more in line with an intermountain snowpack than our typical continental snowpack. In these areas, the persistent slab avalanche problem is close to decreasing to unlikely. Today it will be interesting to look around and see if any avalanches broke deeply into the snowpack. Though from a distance it may be difficult to identify the weak layer as there could be some impressive storm and wind slab avalanches from the last week. 

We have seen another impressive week of accumulating snow in what has shaped up to be an incredible winter. The Gunnison River Basin is now sitting at 149% for this time of year. Here are the recent storm totals from about Sunday through Wednesday.

Irwin: 48" of snow. 2.87" of SWE.

Schofield: 2.6" SWE

Butte Snotel: 1.3" SWE

CBMR: 27" snow.

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