Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

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Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

A Special Avalanche Bulletin is in effect to highlight our dangerous snowpack which is primed for accidents this weekend.  Reports of easily triggered persistent slabs yesterday and several close calls on Friday (Mt. Owen, East Beckwith)  demonstrate why conservative terrain choices are essential.  There has been a steady pattern of large avalanches remotely triggered from gentle terrain this week. The most dangerous slopes face west, north, east, and higher elevations southeast.  You can safely enjoy the fresh snow on slope angles less than 30 degrees that don't connect to steeper slopes above you. Lower elevation southerly aspects offer lower risk options for travel in steep terrain.  

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2.5

    Soft slabs averaging 1 to 2 feet thick in sheltered terrain and larger in wind-loaded terrain will be most sensitive to triggers where they formed over fragile facets, collapsible crusts, or surface hoar layers on west, north, east, and high southeast aspects.  Slab behavior is becoming more challenging as slabs stiffen and thicken, with dozens of recent remote triggers and slabs propagating wider across terrain features.  Human-triggered avalanches and large collapses continue to occur each day and highlight a sensitive snowpack that is near its breaking point.  You can reliably avoid the problem on slope angles less than 30 degrees without steeper slopes above you.    

    A snowmobiler remotely triggered this large persistent slab on Friday (1/2) while riding on the flat terrain below the slope.  These types of avalanches are occurring daily.  

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Northwest winds are drifting the 2" to 4" of new snow into shallow, sensitive drifts below ridges, behind rollovers, and in gullies.   While most of today's wind slabs are relatively small, a triggered wind slab could step down and release a much larger persistent slab described above.  Look for evidence of recent drifting or blowing snow to identify the problem.  Wind slabs will look and feel thicker and stiffer than wind protected snow.  Move to wind eroded or wind sheltered terrain to avoid this problem.  

    An example of a slab avalanche that broke below a leeward ridgeline from last weekend.

Avalanche Discussion

Our snowpack is now paying the price for the long December dry spell, which formed a shallow and weak base below the slabs that have formed since Christmas.  If you're just getting up to speed, check out our weekly summaries and the pattern of recent avalanche activity, which can give you more context to our dangerous setup. 

Observations from the last few days highlight a dangerous snowpack capable of producing deadly and, in some cases, surprising avalanches.  We are seeing diminishing signs of instability in parts of our deeper Northwest Mountains, yet there was a spree of large remotely triggered avalanches there the last few days (Mt. Owen, East Beckwith, Mt. Axtell), including several avalanches that snowmobilers triggered and outran from below the slope.   Feedback from the Southeast Mountains has been less ambiguous; reports of frequent collapses (Ex. Gothic, Double Top) and easily triggered avalanches seem to be the norm.  If the concept of remote triggers is foreign to you, watch this video from Summit County yesterday, which shows two skiers remotely triggering a large avalanche from an adjacent lower-angle slope.  

Last night's new snow will keep the snowpack under distress, and the potential for natural activity will be a low-likelihood threat on wind-loaded slopes today.  Fresh wind slabs are expected to be sensitive today, and they'll generally be larger and more common in the Northwest Mountains, where there's more new snow available to transport.  With today's wind loading pointing at southeast aspects, we've expanded the persistent slab rose to include southeast aspects near treeline, where we've been documenting some small-grained facets above stout crusts a foot or two deep (ex. Axtel, Double Top).  This setup isn't as active or widespread as the well-documented and well-developed weak layers on west, north, and east aspects.  However, it's a potential issue that we are monitoring for, and we have seen evidence of the issue developing above treeline earlier this week.  

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