Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

Heightened avalanche conditions exist on the northern half of the compass where slab avalanches can release on weak snow near the ground, and recently wind-loaded terrain. The most concerning areas are where the two avalanche problems are stacked on top of each other. In those areas, a triggered avalanche could be large and deadly. You can reduce your risk of triggering an avalanche by avoiding wind-loaded slopes, traveling on lower angled terrain, and on southerly facing terrain not highlighted by an avalanche problem. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–2.5

    Persistent slabs up to several feet thick are becoming more stubborn to human trigger and they may not alert you to their presence with obvious signs of instability. The problem is on the north half of the compass, where the foundation to our thickening snowpack is weak and faceted. In steep terrain, the distribution of these slabs is variable because of a widespread cycle that occurred last week. The most concerning terrain for this avalanche problem will be in areas with a strong over-week snowpack structure on slope angles near or above 35 degrees, and on slopes that have seen additional wind-loading. Remember, persistent avalanches can also be remotely triggered from flat terrain below a steep slope, and avalanches might propagate much wider than you expect. Choosing lower slope angles or southerly facing slopes will reduce or eliminate the thread of this avalanche problem.

    This widely propagating persistent slab ran naturally during last week's storm on Mt. Axtell. 

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Throughout the week, southwest to west winds have been transporting snow onto the lee sides of ridgelines and cross-loaded terrain. An extreme wind event on Wednesday further loaded some terrain in usual places, such as lower on the slope than typical, or at below treeline elevations for examples. These slabs remain possible to human trigger. Where these slabs are resting over the persistent slab avalanche problem, a triggered avalanche could step down and take out the whole snowpack and lead to a deadly avalanche. 

     

    Two fresh wind slabs on Scarp Ridge.  The slide on the right is a persistent slab that ran last week. 

Avalanche Discussion

Overnight snow totals look to be in the 2 to 4" range for the NW Mountains and the 1 to 2" range for the SW Mountains. WSW winds at 12,000ft were averaging in the 20 to 30mph range, before tapering off early this morning. That fresh snow and wind will add more fuel to keep the wind slab avalanche problem on the list today, but it will not be enough load to add additional stress to the persistent slab avalanche problem. 

Since the widespread natural avalanche cycle that occurred a week ago on 12/9 and 12/10, (1, 2, 3) we have seen a steep downturn in avalanche activity. On 12/11 there were a couple of persistent slabs human triggered on Gunsight Rd, a skier triggered persistent slab at Irwin on 12/12, followed by a couple of explosively triggered avalanches on 12/13. The extreme wind event rolled in on 12/15 and surprisingly we have only observed a couple of wind slab avalanches from that event. Observations over the last few days have reported the sensitivity of the persistent slab avalanche problem becoming more stubborn with fewer obvious signs of instability, or just a total lack of an avalanche problem on many slopes that have yet to refill since last weekends natural avalanche cycle (1, 2, 3.) 

So what does this all mean? We are tracking a downtrend in avalanche activity over the last week. The avalanche problems are becoming more stubborn to trigger, vs reactive. Our tier 1 travel advice is now warning of heightened avalanche conditions in specific areas, versus the dangerous avalanche condition wording that you have seen most of this week. 

As we head into the weekend the avalanche conditions are expected to stay more or less the same. As backcountry travelers push into more aggressive terrain, we may see more reports of human-triggered avalanches. So tune into where those areas are with heightened avalanche conditions and make some well-informed decisions if you are pushing into more aggressive terrain.

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