Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

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

In sintesi

The threat of large, human-triggered avalanches remains a concern.  Slopes at upper elevations with signs of recent or previous drifting are more dangerous.  You may not experience signs of instability before releasing a dangerous avalanche.  You can find safer options at lower elevations in sheltered terrain, but you should continue to assess the snowpack for cohesive slabs resting above weak snow.   Consider the consequences of triggering an avalanche for the terrain you plan to ride; smaller slopes free of terrain traps provide less risky options. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    Slabs 1 to 4 feet thick have formed over several persistent weak layers in the snowpack:  Weak facets and depth hoar near the ground and surface hoar layers in the upper snowpack. The problem has been most common on northerly and easterly facing slopes this month, and has also recently been active on westerly facing terrain. Persistent slabs have generally become difficult to trigger and signs of instability are infrequent, but if you cross the wrong slope or the wrong spot on a slope, a single collapse can result in a surprisingly large avalanche involving most of the snowpack.  Persistent slabs could break wider than you expect, and they can be triggered from flat slopes connected to steeper terrain above you. You can reduce your risk by traveling on slopes where the problem isn't highlighted above, or by traveling on small terrain features without terrain traps.  You can avoid the problem on slopes consistently less than 30 degrees. 

    A very large natural avalanche on an east-facing slope of Treasury Mtn that likely ran on 12/10

Avalanche Discussion

A trickle of Persistent Slab activity over the past week illustrates the potential danger to backcountry travelers.  A northerly wind event on Thursday night last week released a couple of large avalanches in the Southeast Mountains near Pearl Pass and in the same area skiers remotely triggered an avalanche (video).  Around that same timeframe, a large natural ran in the deeper snowpack of the Raggeds Range, on a high north-facing slope.  On Saturday, skiers on Schuylkill Ridge triggered several shallow Persistent Slabs on Surface Hoar about a foot deep.  On Sunday, nearer the Aspen area, skiers remotely triggered an avalanche on a northeast-facing slope near treeline.  All of this avalanche activity points to a lingering threat of large human-triggered avalanches particularly near and above treeline.  Expect to find larger avalanche size at higher elevations from increased snowfall and drifting which makes a triggered avalanche more dangerous.

Sheltered terrain below treeline has been quieter in recent days hence a drop to LOW danger in the Northwest Mountains.  Poor snowpack structure can be found at lower elevations on the north half of the compass but slabs and weak layers have adjusted to a greater degree making human-triggered avalanches less likely.  In isolated places below treeline, a rider could find a slope capable of producing an avalanche.  The example above from Schuylkill Ridge reinforces this point.  Take the time to dig into the snow and assess snowpack structure for the area you are traveling; if you find strong over weak layering consider selecting lower-angled terrain or pick slopes that offer lower consequences in the event you take a surprise ride in an avalanche.

 

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