Bollettino valanghe

Southeast Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

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

Frequent collapses, easily triggered persistent slabs, and remote triggers highlight dangerous conditions. The remotely triggered avalanche on Snodgrass yesterday continues the streak of large human-triggered avalanches. Safer travel is on wind-protected southerly aspects or simple, low-angle, or small terrain features elsewhere.     

Problemi valanghivi

  • Persistent Slabs

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

    Soft slabs averaging about a foot thick or more 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 large remotely triggered persistent slab on Snodgrass triggered on Sunday (1/5).  

  • Wind Slabs

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

    Northwest winds over the past 24 hours drifted the 3" to 5" of new, low density snow into sensitive drifts below ridges, behind rollovers, and in gullies.   The strongest winds and most favorable transport occurred above treeline, while some exposed near treeline slopes also developed more isolated drifts.    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 in leeward terrain to identify the problem.  Wind slabs will look and feel thicker and denser 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 earlier this season.

Avalanche Discussion

Southeast Mountains: Slabs are an ideal depth for human triggering, and the shallow and weak base below our holiday slabs is slow to improve.  This weekend's observations consistently reported large collapses, easily triggered avalanches, and remotely triggered avalanches.  Ski patrol reports reactive and even touchy conditions as they work into new, untouched snowpacks (Ex. 1, Ex 2).  A large remotely triggered avalanche yesterday near Snodgrass paints the same picture of the obvious danger on terrain harboring persistent slab concerns, most commonly on west, north, and east aspects, and potentially windloaded southeast aspects.  

Northwest Mountains:  Slabs are thicker and obvious signs of instability are diminishing, though we are getting occasional reports of collapses (ex. Coal Creek).  On low-angle slopes that hold the entire season's snowpack, the snowpack structure is gaining strength, and remote triggers are becoming less likely.  These improvements commonly signal a decreasing avalanche danger.  However, we have a unique and challenging setup this season because most of our steep terrain highlighted by the persistent slab rose lost about half of its snowpack to the widespread Thanksgiving cycle.  This means the snowpack is significantly shallower and weaker in start zones compared to low-angle slopes.  This makes it difficult for our forecasters to assess a representative snowpack safely and causes more uncertainty.  These forecaster observations from the Beckwith Range and Marble area (similar setup on the Aspen side) show our forecasters wrestling with this uncertainty and still avoiding avalanche terrain because of it.    Additionally, the wind slab problem is a serious threat at higher elevations.  Observers yesterday reported 16" of new snow in the Ruby Range, and with moderate northwesterly winds over the past 24 hours at high elevations, that low-density snow was easily redistributed into thicker slabs in leeward terrain.  

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