Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

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. A new persistent slab avalanche problem is now creeping into the picture. This avalanche problem is notably larger in size as slabs have propagated across terrain features and are breaking 1 to 3 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. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    On a few specific aspects, persistent slab avalanches are breaking 1 to 3 feet deep and propagating across the terrain. The weak layer is a faceted crust buried just under the most recent storm, and a similar weak layer that was buried 2 storms ago on 3/10. The most notable avalanche released naturally, Thursday, on a SE-facing slope in the Anthracite Range. This isn't an avalanche problem you can manage with a simple ski cut or like a normal storm slab. Detailed snowpack observations are required If you are planning to ride steep terrain near these aspects. Previous wind events are expected to have mostly destroyed these suspected weak layers in the alpine and made the problem less likely at those upper elevations. 

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

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    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 on Wednesday. 

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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