Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 8 months ago. You’re viewing past conditions, not the current bulletin.

Highlights

You can trigger a slab avalanche on northerly-facing slopes and some high-elevation southerly-facing terrain where you encounter a cohesive slab resting above weak snow.  Cracking and collapsing are clear signs of trouble, but don't count on these to alert you to danger.  If you encounter a slab above weak snow, steer towards terrain 30-ish degrees or less to reduce your risk.  You can find safer terrain options on wind-sheltered southerly slopes, which often lack weak faceted snow.  Warm weather could produce a few small wet avalanches on steep southerly terrain.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Last weekend's snowfall and wind drifting formed slabs up to a few feet thick over facets near the ground.  These weak layers are most widespread on the northern half of the compass and exist as collapsible crusts on some high-elevation southeast slopes.  Shooting cracks and collapses are clear warnings, but be aware that direct feedback is decreasing with each passing day.  Persistent slabs can break well above you and be triggered remotely from low-angle terrain adjacent to or below steep slopes.   The most reliable way to avoid the problem is terrain selection: stick to slope angles consistently less than about 30 degrees or travel on terrain that was bare ground through November.  

    This avalanche was remotely triggered on a small terrain feature, releasing the entire snowpack. This avalanche would pile up deeply in a terrain trap or grow larger in bigger terrain. 12/7.

Avalanche Discussion

The formula for a slab avalanche requires a weak layer and a slab above.  Weak snow from early in the season is common across both forecast zones on the north half of the compass and some high-elevation sunny slopes.  When it comes to slab formation, there is some variation between the Northwest and Southeast Mountains forecast zones.  Increased snowfall in the Northwest Mountains over the past two weeks makes encountering strong over weak snow more likely.  Here, you can expect to find slab formation at all elevation bands and better connected through the terrain.  In the Southeast Mountains, less snowfall resulted in smaller, thinner slabs that occupy less of the terrain.  For example, at the lowest elevations in the Southeast Mountains, you may simply find a shallow, weak snowpack that lacks a cohesive slab due to a very thin snowpack, and at upper elevations, slab formation is often patterned on previous wind loading.  In both forecast zones, recent strong winds have played a significant role at upper elevations, leaving some slopes looking loaded and deep while others are scoured and shallow.

With each passing day, the snowpack becomes less reactive to human triggers as slabs weaken from the faceting process in sheltered areas and slowly adjust towards equilibrium in wind-drifted areas.  However, triggered avalanches remain a real concern where you find cohesive slabs over weak layers.  Thoughtfully investigate the snowpack as you travel to identify cohesive slabs and steer away from places that appear drifted or deeper than other terrain features.  The best-looking terrain for recreation, where the snow is often the deepest (north half of the compass or wind-loaded terrain), is the most likely place for you to trigger a slide.  Consider the consequences of being flushed down a steep slope into rocks or trees.

Abnormally warm weather today creates a minor concern for wet avalanche activity on steep sunny slopes.  Carefully monitor the snow surface for wetness and steer away from steep, southerly terrain where you see roller balls.  Loose avalanche activity should remain small, but don't let this 'seasonally confused' problem catch you off guard.

 

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