Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

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

Strong winds last night continued to stress leeward start zones.  Widely propagating and destructive natural avalanches are possible today where winds continue to drift the snow - avoid traveling in windloaded start zones or in runouts below them.  Although avalanches that break near the ground are becoming more stubborn to human triggers, getting caught in one will be difficult to survive.  The most likely terrain to get in trouble today is in windloaded terrain or terrain where snow depths are variable and thinner from wind affects.  

Avalanche problems

  • Persistent Slabs

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

    We have observed a handful of very large avalanches triggered by wind-loading over the past few days, and winds increased last night.  Human triggered or natural avalanches have the potential to break 2 to 6+ feet thick - across entire start zones.  Avalanches that release from high elevation, leeward aspects will be deep and unsurvivable.   You can trigger sizeable slabs that break on weak snow near the ground while traveling on or below steep terrain. They can also release naturally from wind-loading. The most reliable way to manage this problem is by traveling on lower angled slopes that don't connect to steeper terrain above.   If you choose to ride in avalanche terrain, stay on planar or concave slopes with deep, uniform snow coverage, free of shallow spots, rock bands, and recent windloading.  

    A double overhead persistent slab avalanche in the NW Mountains

  • Wind Slabs

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

    A period of strong northwest winds overnight amplified wind transport and fresh wind slab formation.  Slabs of recently drifted snow will be easy to trigger.   You are likely to find them just below ridgelines and in cross-loaded gullies.  Winds were strong enough that you may find drifts further downslope or reaching into below treeline terrain.  Shallow wind slabs have the potential to step down and trigger much larger avalanches.  

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

Avalanche Discussion

In the first two weeks of February, we documented 209 large to very large (D2 to D3) slab avalanches in our forecast area.  In the past week, the frequency of large avalanches has declined - we recorded about 24 naturals and a handful of explosive-triggered slides D2 or larger.  It's been slow to change, but we are starting to see the snowpack structure adjusting from the prolonged loading event and continuous natural avalanche cycle that began in late January.  Although the likelihood of persistent slabs is generally on a decreasing trend, the expected size remains deadly.  The US is averaging more than one avalanche fatality per day this month, a third of which have been in Colorado.  Last night's snow and gusty northwest wind event might have bucked the declining trend in the short term, causing an uptick in persistent slab activity overnight while increasing the threat of wind slabs.   We've raised the danger below treeline in the Southeast Mountains back to Conserable because strong down-valley wind events have a pattern of crossloading below treeline terrain that is more exposed to the wind - spurring natural avalanches that break near the ground and increasing their sensitivity to human triggers.  The danger in windsheltered terrain remains largely unchanged with only a few inches of snow last night.

Most of the persistent slab activity in the past week has been focused in the Southeast Mountains, where the snowpack is weakest.  With the additional stress of last night's wind event, triggering a persistent slab remains likely and naturals are possible in the Southeast Mountains.  In the Northwest Mountains, natural and human triggered persistent slabs are both possible.   In the deeper parts of the forecast area, there are fewer slopes and fewer locations on the slope where you can trigger a persistent slab, but the consequences of triggering a slide has not changed.  Eric's video from yesterday highlights this.   

Last night brough the strongest winds of the week - Cinammon's station saw a period of winds blowing 30 to 40 mph, gusting to 60.  Fresh wind slabs are expected to be larger and more widespread in the Northwest Mountains today because there is more snow available for transport:  Up to 4" from last night along with deeper storm totals from earlier in the week.  

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