Boletín de aludes

Southeast Mountains

Crested Butte Avalanche Center
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Peligro de aludes

Sat
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
3 · Notable
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Desactualizado: este boletín caducó 4 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Recent storm snow and relentless strong southwest winds have formed sensitive slabs on leeward terrain.  The strong winds stiffened the new snow into slabs in some open areas below treeline.  Avoid traveling on drifted terrain features and maintain awareness for stiffer slabs at lower elevations.  In sheltered areas, use caution and carefully assess for instabilities in the upper snowpack before entering steep terrain.  There is the possibility for avalanches to break on weak layers beneath the recent storm snow creating a larger-than-expected avalanche.  Cracking and collapsing are sure signs of unstable conditions.

Problemas de aludes

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1.5–2

    Storm slabs will be likely to human triggers or they may release naturally on wind-loaded terrain; simply avoid wind-drifted slopes.  In wind-sheltered terrain, there is uncertainty as to how reactive this avalanche problem will be. While in wind-sheltered areas look for small, steep test slopes to help identify how reactive Storm Slabs are in the area you are traveling.  

    Blowing snow is creating the largest and most reactive avalanche conditions on wind-loaded terrain features. 

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–2.5

    Over the past 2 weeks, several large avalanches have failed on faceted weak layers deeper in the snowpack.  These include a natural avalanche on Carbonate Hil on Thursday, a remotely triggered avalanche on Mt. Emmons on Sunday, and several human-triggered slides the previous week (Hunter Hill, Snowmass). Persistent slab activity has been infrequent this month and most problematic on wind-loaded terrain.  The current loading event will stress buried weak layers and the expectation is for this avalanche problem to become more reactive again.  Traveling on lower-angled slopes without overhead hazards is the safest method to manage this avalanche problem. 

    A large persistent slab avalanche that was human triggered earlier this month. 

Avalanche Discussion

Over two feet have fallen in the Northwest Mountains and around a foot in the Southeast Mountains with an additional 3 to 6 inches expected today for many areas.  Southwest winds have blown relentlessly, transporting the new snow to leeward terrain forming drifts up to 3 or 4 feet thick.  The winds will continue to transport snow on Friday.  Wind speeds have been strong enough to create atypical loading patterns in some locations like drifting lower in the start zone or open below treeline features.  Visibility has been limited but some natural avalanche activity has been observed on leeward terrain on Whetstone and Mount Emmons.  Irwin Cat-Ski reported explosive-triggered avalanches in drifted easterly terrain. Given the dangerous size of drifted slabs and the continued loading, it seems like a straightforward proposition to simply avoid drifted terrain to greatly reduce your risk of triggering a dangerous avalanche.

There is a Persistent Slab problem listed for both the Northwest and Southeast Mountains forecast zones.  A CBAC forecaster experienced a large rumbling collapse that shot cracks through the top of Climax Chutes.  The group was surprised by the collapse and by the long distance it propagated.  The failure occurred somewhere in the middle of the snowpack 3 feet down on a thick layer of facets.  An observation from Thursday, outside the CBAC forecast area near McClure Pass, stated a skier triggered an avalanche much larger than expected breaking on a crust/facet layer in the upper snowpack.  Luckily the skier was able to ski out of the moving debris before being carried down the slope.  It is not clear yet if these surprises are isolated events or if they point to a broader problem with Persistent Weak Layers in the upper snowpack.

A final round of snowfall and wind will add further stress to the snowpack in drifted terrain and sheltered areas that have buried weak layers.  Conservative decisions and dialing back terrain selection will help you manage the uncertainty of triggering a dangerous avalanche.  Predicting when buried weak layers 'wake up', or become reactive, can be difficult and is best managed with a wider-than-normal margin for error.  

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