Avalanche forecast

Southeast Mountains

Crested Butte Avalanche Center
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Avalanche danger

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

Slab avalanches breaking a foot or more are easy to trigger and some natural activity is expected later this evening.  On west, north, and east aspects,  avalanches can be remotely triggered from flat terrain, and slabs can entrain most of the snowpack once they get moving in more sheltered areas.  Conservative terrain choices are essential:  Smaller, less consequential slopes or low elevation southerly slopes offer lower risk options.  You can safely enjoy the powder on slope angles consistently less than 30 degrees that don't connect to steeper terrain above you.  This terrain map can help you choose simpler terrain.

Avalanche problems

  • Persistent Slabs

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

    Soft slabs of new and drifted snow averaging 1 foot thick will be most sensitive to triggers where they formed over fragile facets, collapsible crusts, or surface hoar layers on west, north, and east aspects.  Slab behavior is becoming more challenging as slabs thicken from windloading and snow, with increasing potential for remote triggers and wider propagation around terrain features.  On these same aspects at mid and low elevations, avalanches will grow larger as they entrain the weak, sugary snowpack under the new snow.  Cracking and collapsing are warning signs to travel on slope angles less than 30 degrees.    

    Older, hard slabs exist below the storm snow on some leeward slopes and can produce avalanches that are more surprising or difficult to manage. Identifying the locations of these older slabs is now challenging beneath the new snow.  

    A skier triggered slab avalanche that broke on weak facets and gouged to the ground above the Slate River on 12/27.

  • Storm Slabs

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

    While most avalanches are expected to break on persistent weak layers described above, instabilities within the storm snow or breaking on top of crusts lacking persistent weak layers are also a concern around the compass, especially in wind drifted terrain.  On southerly aspects, monitor storm totals and assess how well instabilities are bonding to slick crusts before riding in steeper terrain.  Small, steep test slopes can be used to gather feedback before riding in bigger terrain.  Shooting cracks are signs to choose mellower terrain.  

    An example of a storm slab from the archives.

Avalanche Discussion

Storm totals on our well-advertised weak layers average about 2 feet (up to 2.2" SWE) in the Northwest Mountains and 1 foot (up to .8" SWE) in the Southeast Mountains.  Easy triggering of these soft slabs over fragile weak layers is expected in both forecast zones; the main distinction between the two zones is the average size and distribution of our new slabs: slabs are twice as thick and more widespread in the deep zone.  It's important to note that in wind-sheltered terrain, once slabs are triggered, they will entrain most of the weak snowpack below and grow larger than you might expect (See Eric's observation yesterday from the Slate).  

The bulk of natural activity will coincide with periods of heavier snowfall and windloading.  We likely saw the first surge of naturals with the pulse of snow last night.  A lull in snowfall through mid day will cause a notable downturn in natural activity, and the danger rating may fit better with Considerable across the entire forecast area this morning.  For the Northwest Mountains, snowfall rates increase later this afternoon or overnight, causing the natural activity to resume and the danger to rise to High.  This isn't the hard smash, complete flush we saw during the Gizzard Blizzard. The slower loading on variable weak layers will bring some slopes to their natural tipping points while others will hang in the balance waiting for human triggers.  

 

Regions covered