Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

A few more inches of snow will accumulate today and southwest to westerly winds will continue to transport snow onto drifted features at upper elevations.  Terrain features with the greatest concern will be those with recent or active wind-loading.  You can trigger shallower avalanches in recently formed surface slabs or broad, deep failing avalanches near the ground.  Below treeline slopes have seen little loading for several days but can still produce dangerous slides.  At lower elevations look for shallow areas on slopes for trigger points, or thinner, rocky-looking terrain with highly variable snow depths to clue you into an increased chance of triggering an avalanche.

Avalanche problems

  • Persistent Slabs

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

    This past week avalanches have been breaking 2 to 6+ feet thick, across entire start zones and producing destructive amounts of debris in their runouts. You can trigger avalanches while traveling on or below steep terrain. They can also release naturally from wind-loading or snowfall. The best way to reliably manage this problem is by traveling on lower angled slopes that don't connect to steeper terrain above. The likelihood of human triggering is decreasing towards possible while increasing winds will keep the threat of avalanches more likely at near and above treeline elevations due to wind-loading today. 

    A double overhead persistent slab avalanche in the NW Mountains

  • Wind Slabs

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

    An increase in westerly winds for the past two days has drifted snow at upper elevations forming fresh surface slabs on leeward terrain features.  Expect newly formed Wind Slabs to be sensitive to the weight of a person or machine.  You are likely to find them below ridgetops and underneath cornices on leeward aspects.  They can also be found on cross-loaded gullies and behind ribs on more windward aspects.

    A fresh Wind Slab failed on Mount Emmons sometime Friday, 2/19.

Avalanche Discussion

Today's weather, namely westerly winds strong enough to transport snow and a few additional inches of snowfall, will maintain the increased concern on drifted features at upper elevations.  Two recent observed avalanches from yesterday help to confirm this.  Take a look at this observation for photos of a fresh Wind Slab in Red Lady Bowl and a deep failing avalanche out the Brush Creek drainage on Timbered Hill.  Both ran on drifted southeasterly terrain, but the Wind Slab was not quite deep enough to bury a person, whereas the Timbered Hill avalanche failed deeply and certainly would bury, injure or kill you.  It is a bit of a guessing game as to which drifted slopes will fail in recently formed surface slabs and which can fail deeply producing a hard-to-survive avalanche.  Over the past couple of days, it appears as the deeper failing avalanches are coming from areas in the Southeast Mountains where the snowpack, in general, is shallower, but I would not rule out this possibility in the Northwest Mountains.  With more loading from wind and snowfall today, it would be prudent to give a wide margin to cover the uncertainty for drifted slopes. 

Below treeline slopes in both the Southeast and Northwest Mountains have three or more days without significant loading.  For slopes with a deeper snowpack, generally more than 150cm, it has become harder to trigger avalanches but certainly not impossible.  Below treeline slopes with a deeper snowpack are more commonly found in the Northwest Mountains.  For below treeline slopes with a deeper snowpack, you may need to find a trigger point on a slope where the slab thins near rock outcrops or thinly buried bushes or rocks to initiate failure.  Slopes below treeline with shallower snow depths say closer to 130cm or less, it will be easier for you to produce failure and impact the weak layers below.  Shallower slopes are more commonly found in the Southeast Mountains, but also exist in the Northwest Mountains.  You can take a look at this observation illustrating a very poor-looking structure with multiple collapses (a sign of instability) in a shallower snowpack below treeline.

The mountains around Crested Butte are just coming out of a long period of snowpack growth with significant snowfall and multiple avalanche cycles at the end of January and the first few weeks of February.  Overall stability has begun to improve, but we are not out of the woods by any means.  This winter's avalanche conditions have proven tragic across the mountain west, throughout Colorado, and sadly right here in Crested Butte.  If your 'jonesing' for steeper and more consequential terrain but have lingering doubts about a given slope, the simplest and safest solution is to give it more time and wait for safer conditions later this spring.

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