Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

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

Although the odds of triggering an avalanche are decreasing with each day of dry weather, the consequences remain serious. If you find the wrong slope, you can bring down a large and dangerous avalanche that breaks several feet thick on old, weak layers.  The north half of the compass near and above treeline is most worrisome, or any slope that has seen significant windloading in recent days.  If you are traveling in steep terrain, choose slopes with deep, uniform snowpacks to reduce your risk.  Default to lower slope angles or terrain below 10,500' when in doubt.    

Problemi valanghivi

  • Persistent Slabs

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

    Potential continues for human and remote-triggered slabs that fail 2 to 4 feet deep on depth hoar, facets, and faceted crusts.  Northerly and easterly facing terrain near and above treeline has been most active this month due to thicker slabs over well-developed weak layers.  Recent northerly winds have expanded activity onto some high, southerly and westerly aspects.   Cracking and collapsing are obvious signs of instability, although your first clear signal could be a dangerous avalanche due to variable and diminishing feedback.  In the Northwest Mountains, slabs are most likely to be triggered in terrain where slabs are thinner or variable in depth from wind effects. The most reliable way to manage this problem is by choosing slopes less than 30 degrees. Wind-protected southerly aspects and elevations below ~10,500' typically offer safer snowpacks, where slabs are less common and weak layers are often capped by stronger crusts. 

    A large persistent slab ran naturally on the west side of Mt. Baldy on Saturday.  

Avalanche Discussion

As the likelihood of triggering an avalanche continues to decrease, our travel advice is shifting toward Moderate danger and avoiding specific terrain features rather than broad aspect categories. Two different snowpack processes are helping conditions slowly improve, and the most problematic features depend on where you are traveling in the forecast zone.  There's always uncertainty and spatial variability when it comes to managing persistent slabs, but here are some general strategies if you are accepting more risk and traveling in avalanche terrain on the problematic aspects.  

Relatively deep snowpacks: In areas where snow depths exceed about 4 or 5 feet—the Ruby Range and surrounding terrain—slabs are becoming increasingly difficult to trigger. Thick, dense slabs limit how effectively a rider’s weight impacts the weak layer, while ongoing rounding is slowly strengthening the snowpack (see video from Schuylkill Mtn yesterday). In these areas, the primary concern is shallow or variable snowpack features such as rock bands, pungie trees, and wind-affected slopes where slabs thin.  Note that shallow areas are not always obvious, and the consequences here are deadliest.  The recent avalanche on Mt. Baldy illustrates terrain where slab depths are variable due to wind.  

Relatively thin snowpacks: Where snow depths are less than about 2.5 feet—across much of the Southeast Mountains and lower elevations—the thinner, softer slabs are losing cohesion as faceting continues. Here, the most concerning features are slopes where slabs remain stiff and cohesive, typically due to previous wind loading. Safer travel options exist where the snowpack has been wind-eroded or where slabs have lost cohesion in wind-protected terrain. This observation from Hunter Hill illustrates the pattern. 

The Goldilocks zone: Snowpacks around 3 feet deep sit in a challenging middle ground. Slabs here can have enough cohesion to propagate a fracture, but remain thin enough for a skier or rider to impact the weak layer—sometimes even on uniform, wind-protected slopes. These slopes are not universally unstable, but they are harder to assess using terrain and snow surface clues. This observation from Axtell provides a good example of this “Goldilocks” setup.

Upcoming Outreach Events:  

Jan 13 Fireside Chat:  Kim Grant from Silverton Mountain at Zuni West Brewing 5-7 pm

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