Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

1 to 3" of new snow has accumulated overnight, with another 3 to 5" of snow forecasted today. On the northern half of the compass that new snow is accumulating on an exceptionally weak snowpack. Confidence is low on just how much new snow it will take to form a widespread soft slabs avalanche problem in these areas, that will become sensitive to human triggering. Soft slabs that are 4 to 6" thick will form first near ridgelines where westerly wind gusts are drifting the new snow. As the day progresses, thin soft slabs may also become sensitive to human triggering in sheltered areas. Keeps those eyes open today for changing conditions. Use small hand pits and test slopes to identify if soft slabs have formed in the new snow, or if the new snow is simply just adding volume for loose snow avalanches. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    New snow is accumulating on an exceptionally weak snowpack. Once a slab forms in the new snow, it will become possible to human trigger this avalanche problem. These slabs would also develop wide propagation like a Persistent Slab Avalanche Problem. The Persistent Weak layers in the old snow are well documented. So, the observations that need to be made are; when do these soft slabs start to form, and where are they located in the terrain.

    Example of a Shallow Soft Slab forming in new snow.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    On very steep terrain sheltered from the sun and wind, you can trigger sluffs where the snow surface is loose and cohesionless. These skier triggered loose avalanchesfrom Climax Chutes on Thursday, 12/3, highlight the problem. The recent new snow will now add volume to this avalanche problem, helping a triggered sluff grow larger as it accumulates mass and descends through the terrain. 

Avalanche Discussion

When uncertainty is present, it's best to error on the conservative side and expect the worst. In that case, it would be to anticipate soft slab avalanche to form even in the sheltered areas of the Northwest Mountains, and for a more specifically located wind slab to form in the SE Mountains where new snow accumulations are less. If the worst-case conditions are anticipated, then you shouldn't be caught off guard by a potentially dangerous avalanche problem. If soft slabs do not form in the new snow, then loose snow avalanches or sluffing will be the only avalanche problem to manage.

Dangerous avalanche conditions are forecasted to develop in the NW mountain by late Saturday afternoon if the snow forecast verifies. Check-in for tomorrow's avalanche forecast and anticipate a rising avalanche danger trend heading into the weekend. 

Below is yesterday's Forecast discussion highlighting the weak snowpack and sluffing avalanche problem due to that cohesionless snow. 

The shallow snowpack around Crested Butte has been weakened and faceted by cold temperatures and valley inversions. This faceted snowpack has produced human-triggered loose avalanches for the past week. The largest of these avalanches have occurred in terrain close to Crested Butte where strong valley inversions have created a cohesionless snowpack the lacks any kind of support. You can check out some observations of this avalanche activity in these observations from Happy Chutesand Climax Chutes. Observations from the past week out of the Northwest Mountains have shown the Dry Loose avalanche problem to be even smaller, involving just the surface snow. Beneath the weak surface often lies a more supportive base that prevents loose avalanches from gouging to the ground. You can look at these observations from the Northwest Mountains to better understand the problem where the snowpack is a bit stronger (Schuylkill Ridge, above Pittsburg, Purple Palace, and Anthracites). One way to help manage this avalanche problem is by performing ski cuts to flush snow prior to descending, and to get a feel for how the snow will behave. The snowpack in alpine terrain is denser than slopes at low elevations and offers a significantly reduced chance of encountering the Dry Loose avalanche problem.

Regions covered