Bollettino valanghe

Gunnison

Crested Butte Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

A Special Avalanche Bulletin is in effect to highlight our dangerous snowpack which is primed for accidents this weekend.  Several close calls yesterday (Mt. Owen, East Beckwith) and a steady pattern of large, remotely triggered avalanches demonstrate why conservative terrain choices are essential.  Patience is a virtue.  The most dangerous slopes face west, north, east, and high-elevation southeast.  The most reliable way to stay safe this weekend is by traveling 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
    1.5–2.5

    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
    1–2

    Westerly winds have redistributed the recent ~6" of snow into thicker drifts in leeward and crossloaded terrain.  Today's increasing winds will form another generation of wind slabs that will be easy to trigger later this evening.  While most wind slabs are relatively small, slopes with large fetches and efficient drifting could harbor larger and more dangerous slabs.  Moreover, 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.  Steer away from these drifts below ridgelines, in gullies, or behind rollovers to avoid the 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. 

We remain in entrenchment mode because of several unique early-season pitfalls that make our snowpack especially challenging.  The first was our Thanksgiving storm and avalanche cycle.  On paper, it gave us an above-average snowpack, but in reality, almost all of our steep terrain avalanched naturally during the cycle, leaving an unusually shallow snowpack.  Then, a near-record dry spell in December caused that snowpack to become very weak, even in the parts of our zone that typically offer a stronger and deeper base. Finally, the past 10 days of incremental loading have brought the snowpack near its breaking point on many slopes.  Large, deadly avalanches have been remotely triggered by skiers and snowmobilers every day this week.  Additionally, we see more large natural avalanches every time it snows and the wind blows.  The heavy snow squalls and blustery winds accompanying today's late afternoon/early evening cold front will probably cause more natural activity, especially on wind drifted slopes.    

Here's the tricky part: in the low-angle terrain of some of our deeper areas, the snowpack may be quieting down underfoot, luring you towards a false sense of security. But as soon as you move off of those low-angle slopes that hold the whole season's snowpack and onto a steeper avalanche slope that sat very shallow and weak through December, the snowpack structure changes and slabs are likely to be more sensitive.  The exception to this challenging setup is on southerly aspects, where sun and warm temperatures during our dry spell formed thicker and stronger crusts on the steepest sun-baked slopes.  However, we have observed a recent uptick in unstable tests and natural avalanche activity likely breaking on a sporadic and thin layer of small-grained facets above this crust, primarily on high-elevation, southeast aspects. You should carefully evaluate the snowpack for similar issues before traveling on any steep southerly facing terrain, especially at higher elevations.   

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