Bulletin d’avalanche

Southeast Mountains

Crested Butte Avalanche Center
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Danger d’avalanche

Tue
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

In the Southeast Mountains, heightened avalanche conditions exist where winds have recently added stress to buried weak layers in the middle or bottom of the snowpack.   Numerous large persistent slabs ran naturally yesterday in the adjacent Northwest Mountains.  Triggering similar avalanches will be possible today in leeward terrain features. You can remotely trigger avalanches from below steep connected slopes.  Wind protected terrain is offering safer riding conditions today.  

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Dozens of large and dangerous persistent slabs have run in the past two days in the Northwest Mountains, but natural activity has been limited in the Southeast Mountains, where storm totals were small.   In wind drifted terrain, slabs have the potential to break several feet thick on facets and faceted crusts in the upper snowpack or depth hoar near the ground.   This large avalanche triggered exemplifies how persistent slabs can be remotely triggered from below a steep slope and propagate widely across the terrain.  Persistent slab avalanche activity this month has been most common on the east quadrant of the compass at higher elevations.  Do not expect to see obvious signs of instability before triggering an avalanche: we had numerous reports of "no signs of cracking or collapsing" yesterday while witnessing ongoing natural avalanches.   Give yourself a wide margin for error when assessing and managing persistent slabs.  

    1/31: Natural persistent slabs that were triggered on Sunday by solar warming

Avalanche Discussion

NW Mountains Discussion

We've seen a doozy of persistent slab avalanche activity in the Northwest Mountains this weekend. See the gallery below or our observations page for photos.  The first wave of avalanches ran on Saturday from exceptional storm totals exceeding 20" in the Ruby Range, paired with bouts of gusty westerly winds.  Yesterday's activity was caused by a rapidly consolidating snowpack under strong solar and warming temperatures.  Ongoing natural loose snow avalanches triggered a number of these avalanches.   This video captures a sequence of persistent slab releases on Mt. Bellview throughout the day yesterday. Wild!  Even with our strong warnings and a special avalanche bulletin yesterday, we were still surprised at how much natural persistent slab activity released during the day.  We even saw natural avalanches running on east aspects well after the slopes had moved into the shade.  With the initial heat shock now past us, we are expecting a downturn in natural activity today but I'm not sure we're out of the woods yet for naturals.  We'll see warm temperatures again today, and high clouds moving in by midday. Clouds may put a damper on heating, or they may amplify heating with the greenhouse effect.  Either way, buried weak layers remain sensitive to human triggers, so choose your terrain carefully.  The focus of avalanche activity yesterday was on east, southeast, and a few south-facing slopes.    The more southerly aspects will offer better stability this morning while surface crusts remain frozen, but if the snow surfaces thaw later today, consider them on the scary list as well.  Where is the safest riding today?  You guessed it, lower slope angles and small, rolling terrain features where slides will be smaller if they break.  Remember that you can remotely trigger an avalanche that is connected to steeper terrain above.  

SE Mountains Discussion

We haven't observed any natural persistent slabs in the Southeast Mountains (yet) from this event.  I expect a few ran on Saturday from windloading.  The Southeast mountains missed out on Saturday's bounty of snowfall (they picked up 1" to 3" from this storm), so persistent slab problems generally remain localized to wind drifted terrain, mostly near and above treeline.  The distribution rose reflects the slopes where you are most likely to find well-developed slabs over weak layers in the middle and bottom of the snowpack.  The likelihood of triggering a persistent slab is lower, and the expected size is smaller, thus the danger is lower in the Southeast Mountains.  If you're riding in the alpine and find a slope with deep and attractive snow coverage, it is probably suspect.  Below treeline, reactive persistent slab structures are rare - slabs haven't developed in most of the terrain.  Below treeline exceptions are most likely to be found where winds have drifted snow or where there are thin crusts below this week's snow to help communicate failures across slopes.

Régions couvertes