Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
1 · Gering
Waldgrenze
1 · Gering
Unterhalb
1 · Gering
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Kernpunkte

Normal caution is expected today while keeping an eye out for any potentially unstable snow on isolated terrain features. The last persistent slab avalanche was observed on March 8th. This low probability the but high-consequence avalanche problem is most suspect where the total snowpack is shallow and variable in depth. Wet avalanche concerns are decreasing today, with isolated exceptions being areas where you find your feet sinking deeply into a wet snowpack.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    2–3

    In the Northwest Mountains, high-consequence slabs breaking on older weak layers have become isolated and difficult to trigger. The last observed persistent slab avalanche occurred on March 8th in this forecast area. As snow surfaces refreeze following a week of warm weather, concerns for this problem on shoulder aspects will be even further reduced. Any lingering persistent slabs would most likely be triggered from an unusually shallow or previously wind-eroded slope where the total snowpack height is below average.  Large cornice falls could act as triggers as well. Persistent slab avalanches can be remotely triggered from low-angle terrain and break deeper and wider than you might expect.  The most problematic structures are on shallower slopes on the north half of the compass.  Slope angles consistently less than 30 degrees are a reliable way to avoid the problem when in doubt.  

    The crown of a very large persistent slab remotely triggered by snowmobiles on March 8.  This slope is west facing and eroded by seasonal winds, making for a shallower and more problematic snowpack than other slopes. 

Avalanche Discussion

Saturday is looking to be a transition day, from the previous wet avalanche concerns over the last week to new snow avalanche concerns developing on Sunday. Cloud cover should keep any wet loose avalanche concerns in the rearview mirror. Isolated concerns that could linger today, would be for areas that the snowpack hasn't had a chance to refreeze. Those areas would be identifiable as you would sink deeply into wet snow. At lower elevations the snowpack will be holding onto the heat that it absorbed yesterday, after cloud cover and a little bit of new snow, didn't let that heat escape last night in the form of long-wave radiation loss. A triggered avalanche in this type of snowpack would be a hybrid between a wet slab and a persistent slab avalanche. New snow avalanche concerns will be on the list for Sunday. 

The last persistent slab avalanches were observed on March 8th in the Northwest Mountains, and more recently on March 16th in the SE Mountains. Concerns for additional persistent slab avalanches have mostly been for areas with a relatively shallow snowpack where persistent weak layers have remained more pronounced. Many of those same areas have seen meltwater draining through the snowpack recently, and once that snowpack has a chance to refreeze we will no longer be dealing with this avalanche problem in those areas. An observer yesterday found an area with a wet snowpack producing shooting cracks down to moist facets. There are still a few isolated areas around Crested Butte where we could see similar conditions today once temperatures climb back above freezing. Those isolated conditions would be in areas where you find yourself sinking deeply into a wet snowpack, most likely on a shoulder aspect such as east or west, that also has persistent slab snowpack structure. 

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