Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

A couple of days now separate us from the last storm, and storm slabs breaking in the recent round of snow are becoming less likely to encounter. Caution is still advised around previously wind-loaded terrain at near and above treeline elevations and on very steep slopes. The persistent slab avalanche problem is notably larger in size and slabs are capable of propagating across terrain features and are breaking 1 to 4 feet deep. At least one notable natural avalanche occurred in our forecast area yesterday, and a couple of close calls occurred just outside our forecast area in Marble. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    There are faceted weak layers in the upper, middle, and bottom of the snowpack that remain a concern in some terrain. The most concerning slopes include those that held an unusually shallow and weak snowpack prior to last weekend's storm, where snow depths are currently less than about 5 feet (150cm) deep, or in wind-effected terrain with variable snow depths. Recent "step-down" avalanches in West Brush Creek and East Brush Creek highlight the potential for avalanches to break on deeper weak layers in the Southeast Mountains. Two faceted crusts are now buried in the upper snowpack on easterly and westerly-facing slopes. The most notable avalanches on these interfaces have occurred in the NW Mountain forecast area where they are buried by more snow, but with more time we suspect that a pattern will also emerge in the SE Mountain forecast area. Carefully assess the snowpack structure and give yourself a margin for error in handling this problem. There is a high degree of variability across the region and on different aspects.

     

    A D2.5 persistent slab that ran naturally 3/16 during a warming event. 

  • Storm Slabs

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

    Recently formed Storm slabs are about 6 to 20" thick. They remain the most suspect on previously wind-loaded terrain and on slope angles around 40 degrees. Look for cracking and signs of instability on small/steep test slopes before moving into bigger terrain. In wind-sheltered areas, this avalanche problem has become stubborn or non-existent and the primary concern will be the persistent slab avalanche problem. 

    If we see a few hours of strong solar input this afternoon, this avalanche problem will become more reactive and continue to transition into a loose wet avalanche problem.

    Example of a small test slope that produced results yesterday. 

Avalanche Discussion

2" to 4" of snow water equivalent has accumulated across our areas in the last week, during two notable storms. The primary avalanche problem was storm slabs during those storms. With yesterday's warming event, a new pattern of persistent slab avalanches is becoming more clear. We have been keeping an eye on faceted crusts that were buried on 3/10 and again on 3/15. Slab avalanches on these layers initially behaved like storm slabs. Continued observations are now noting that slab avalanches on these weak layers are propagating across terrain features and not healing as fast as the storm slab avalanche problem. A persistent slab avalanche problem was added to the NW Mountain forecast and these will be just another potential weak layer in the SE Mountains that have had a persistent slab avalanche problem for some time now.  

The storm slab avalanche problem will continue to phase away as we head into the weekend. However, the next warming event will increase concerns for this new persistent slab avalanche problem, and again for wet avalanche problems. 

Events:  The Al Johnson race is Sunday, March 19. Information and registration are here.  Day of race registration and bib pick up 9-11 a.m. at the Adventure Center in Mountaineer Square. Proceeds go to the CBAC.

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