Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

The threat of triggering a large and dangerous avalanche continues, evidenced locally by continued reports of rumbling collapses and persistent slab activity, along with numerous close calls and a tragic accident in Colorado.   Slopes with a relatively shallow snowpack or rocky terrain are most problematic.  As the upper snowpack gets wet on sunbaked slopes, slabs may become more sensitive to triggers or small wet loose avalanches can release.  You can find lower-risk riding and great powder in wind-protected, shady terrain where the snowpack is uniform and consistently deeper than about 5 feet deep.  

Avalanche problems

  • Persistent Slabs

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

    January storms formed slabs averaging 2 to 4 feet thick over widespread persistent weak layers lower in the snowpack.  Persistent slab avalanches have the potential for wide propagation and remote triggering,  and may not give any warning signs. Avalanche activity has diminished in the past week because we have moved further away from the last loading period under mild weather. That downturn is mainly due to the slabs gaining strength, but the weak layers have only shown minor improvements in some areas. Those weak layers are still very capable of producing large and deadly avalanches.  The easiest and most reliable way to manage this problem is to ride on slopes consistently less than 30 degrees in steepness.  Other strategies for reducing your risk include riding on slopes where the problem has recently avalanched away, avoiding trigger points where the snowpack thins near rock outcrops or wind-eroded terrain features, or traveling where the snowpack is consistently deep (>150cm) and uniform. 

    1/24: Winds have created variable slab thicknesses on slopes like this.  Red circles are areas where I would expect the slab to thin out and be easier to impact buried weak layers.  

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    As the snow surface gets wet later today, stay alert for shallow wet avalanches starting from very steep, sunbaked slopes, especially near rock bands.  Look for natural avalanche activity, rollerballs, or pinwheels shedding from hot slopes to warn you of the developing problem.  Wet loose avalanches can cause trouble if they push you into a terrain trap or if they trigger a larger persistent slab.  Choose lower slope angles or colder aspects to avoid the issue.  

    1/28: Small wet loose avalanches on a hot, rocky slope.    

     

Avalanche Discussion

Don't let the spring-like weather fool you, it's still a winter snowpack.  Even 10 days after the major loading period has ended, we continue to observe sporadic natural and triggered persistent slabs (ex. Taylor Pass yesterday). This unusually long tail of instabilities highlights how tricky our snowpack is.  Increased winds on Saturday brought a small uptick in persistent slab activity, including large avalanches on Bellview and Purple Ridge in the Northwest Mountains, and numerous persistent slabs that appeared to fail in the past few days in the Southeast Mountains.  Since the stormy period ended on January 18th, we've documented about a dozen persistent slabs in each of the two forecast zones, on nearly all aspects.  There's been more activity than normal on westerly and southerly aspects, where the snowpack is shallowest and weakest, and thus most sensitive to small environmental changes or triggers.  The next test for our snowpack is the introduction of some meltwater on sunbaked slopes this week.   Because it is only late January, a lower sun angle and hard freezes at night will temper this warmup.  However, we started to see some small wet loose activity yesterday, and that pattern should continue under a warming trend over the next couple of days.  Given how poor the snowpack structure is on some southerly aspects, I won't be surprised to see a few more large naturals as softening persistent slabs get overrun by wet sluffs running downslope, or maybe even an isolated wet slab or two from a hot, rocky slope.     

With the blue sky, spring-like weather, and diminishing signs of instability, it's easy to get complacent or overconfident with the snowpack. Of the seven people caught in large to very large avalanches around the state since Friday (Ex. 1, 2, 3, 4), none of them observed cracking, collapsing, or other signs of instability before triggering avalanches.  Look through the media gallery below or our observations page to remind yourself that the gremlins are still lurking, and make thoughtful route plans in the mountains so you don't get surprised by a large avalanche this week.  Without additional loading, our buried weak layers are on a very gradual improving trend.  Those changes are more favorable where the snowpack is deeper and faceted grains are quicker to gain strength.  Furthermore, the deeper the snowpack, the harder it is for skiers and riders to impact those layers.  It's far from a guarantee, but if you are riding steep terrain, you are better off riding where the snowpack is deep compared to thin and variable. Thin snowpacks are more common in the Southeast Mountains, or wind-affected terrain in either forecast zone.  Default to lower slope angles when in doubt.  

Events: Our next Fireside Chat is this Sunday, February 4 at 6 p.m. at High Alpine Brewing Company in Gunnison. A local snowmobiler will talk about his experience with an avalanche burial and rescue while snowmobiling last year.

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