Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

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

In sintesi

You can trigger loose avalanches on steep slopes where you find a soft and weak snowpack and trigger stiff slabs on previously drifted slopes.  A few inches of recent snowfall has obscured visual clues to the location of slabs on leeward terrain; you can avoid this problem by selecting wind-sheltered features.  In wind-sheltered areas with a weak snowpack, you can reduce the chance of triggering a loose avalanche by keeping slope angles to 35 degrees or less.

A storm system arriving this afternoon is not expected to change today's danger rating. However, if you encounter 6 inches or more of new/windblown snow this afternoon, expect increasing avalanche danger.

Problemi valanghivi

  • Persistent Slabs

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

    Since 12/9, several northwest-to-southwest wind events formed slabs around a foot thick or more in heavily wind-loaded terrain features. These wind-drifted slabs are most commonly found at higher elevations below leeward ridgelines and rollovers on east to northeast-facing terrain. They can also be found around the northern half of the compass in a few concave terrain features that collect drifting snow, such as gullies. These slabs are often hard and difficult to trigger, but some formed over weak, faceted snow that is slow to heal, making for variable feedback.  This week, a few inches of snowfall have obscured the evidence of previous wind-loading and made it more difficult for you to identify the problem.  Use caution around leeward terrain features, particularly if you feel stiff snow a few inches below the surface, as this is likely an old, hard slab. 

    A booming collapse and shooting cracks triggered on 12/21 on this heavily drifted slope demonstrate the potential to trigger a hard, persistent slab avalanche.  

  • Loose Dry

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

    In terrain protected from the sun and wind, most commonly on the north-to-east aspects, you can find a weak and cohesionless snowpack.  In these areas, you can trigger dry loose avalanches in terrain steeper than 35 degrees.  Point-release instabilities are relatively small and easy to recognize. Still, they can spell trouble by pushing you into trees, rocks, or gullies, especially in long, steep terrain where they will gouge to the ground and gain more volume.  Use sluff management techniques or move to less consequential, lower slope angles to manage the problem.  A few inches of new snowfall (Monday night, 12/23 and Wednesday,12/25) added volume to this problem and slightly increased avalanche size.

    Skier triggered dry loose avalanches on Schuylkill Ridge. 12/19.

Avalanche Discussion

Conditions have slightly changed this week due to a few inches of new snow.  The Dry Loose avalanche problem has incrementally increased in size due to more snow available for entrainment.  Here are some examples over the last few weeks (Snodgrass, Schuylkill Ridge, Axtell, Emmons, Elk Creek).  Although most loose avalanches remain small in size, they have enough power to knock you down and drag you into rocks or trees, and some isolated, longer slopes with large vertical relief may be able to produce avalanches large enough to bury you.

The bit of new snow also obscured the visual clues for the Persistent Slab problem making it harder for you to identify and avoid.  Here's clear evidence of the problem from just this week: collapses on Anthracite Mesa Tuesday, a rider released a hard slab in Red Lady Bowl on Sunday, collapsing below Schuylkill Peak on Saturday (video), and a skier-triggered slab last Friday on Mt. Tilton.  Use caution as you travel through wind-affected terrain, and be sure you are not traveling over old, hard slabs obscured by a few inches of recent soft snow.  Head towards wind-sheltered terrain when in doubt.

Looking to the near future, an incoming storm arrives this afternoon and lasts through early Saturday.  Expect conditions to become dangerous sometime on Friday.  New slabs will likely form first on wind-drifted terrain and then spread to sheltered areas as snowfall totals increase.  Given the weak nature of the snowpack, it will not take much new snow and wind to create natural avalanches and human-triggered slides.  Even though the new slabs might be relatively thin, their debris will increase in size due to the available snow for entertainment as they run.  Be prepared to change your terrain choices if the incoming storm meets or exceeds forecasted totals.  

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