Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Avoid traveling on steep slopes that have received significant wind loading in the past week.  There is a clear pattern of persistent slabs breaking over a foot thick on leeward slopes near and above treeline.  The latest additions are a pair of large hard slabs that ran Saturday night on Mt. Baldy and a skier-triggered hard slab on Ruby Peak.   Wind-protected slopes offer safer riding and better snow quality: you'll have to manage for small loose dry avalanches in sheltered, lower elevation terrain.   

Avalanche problems

  • Persistent Slabs

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

    Over the past week, several northwest to southwest wind events have formed new slabs around a foot thick. These wind-drifted slabs are most commonly found at higher elevations below leeward ridgelines and rollovers on east and northeast facing terrain. They can also be found around the northern half of the compass in a few concave terrain features that collect drifting snow, such as gullies. These slabs are often hard and difficult to manage, breaking unpredictably and with inconsistent feedback underfoot.  Because many of them formed over weak, faceted snow, instabilities are slow to heal.  Assess recent wind-loading patterns and avoid previously wind-loaded terrain features, especially in high-consequence terrain.   

    In very isolated areas on the northern half of the compass, there is lingering potential/uncertainty for triggering an avalanche up to several feet deep on weak layers near the ground. This would require a slope that has retained its full-season snowpack without flushing during the widespread avalanche cycle in late November. 

     

     

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    In terrain that has been protected from the sun and wind, the snowpack is growing increasingly weak and cohesionless, and human-triggered sluffs are becoming larger or more common.  These point-release instabilities are relatively small and easy to recognize, but they can spell trouble if they push you into trees, rocks, or gullies, especially in long, steep terrain features where they gain more volume.  Use sluff management techniques or move to less consequential, lower slope angles to manage the problem.  

    A small dry loose avalanche that was skier triggered from a very steep slope and then ran into lower slope angles once it gained volume.  

Avalanche Discussion

When a few inches of new snow and increased winds trigger a handful of natural hard slabs up to D2 in size, you know that's a sign of a crappy weak layer.   Horrible weak layers are pervasive across our mountains on west, north, and east aspects following the dry spell and shallow snowpack left behind by the big Thanksgiving cycle.  By itself, weak snow is not all that dangerous but requires caution in very steep terrain where the cohesionless, sugary snow gains volume as a point-release avalanche.  The bigger hazard is anywhere that slabs have formed over this rotten snowpack.  With relatively modest amounts of snow (up to 18" in the NW Mountains and a few inches in the SE Mtns) and big wind events in the past week, slabs have formed on specific, wind-loaded features in the snow-favored areas and more isolated features in the snow-starved areas.  Because these slabs are formed almost exclusively from wind loading, if you recognize the features that collect wind loading from NW to SW winds, you can identify the most problematic slopes at higher elevations. If you'd prefer a simpler approach (with better snow quality), seek out the soft snow in wind-protected terrain and manage for small point releases if your slope angles tilt steeper than about 37 degrees.  

Looking at the avalanche patterns since our first in a series of wind events started a week ago, you'll see where slabs have been most active:  east and northeast-facing slopes above 11,000' in the Northwest Mountains.  This makes sense because those aspects held rotten weak layers on their bed surfaces, and have now received the brunt of wind loading.  The NW Mountains have been significantly favored by snowfall, so more snow was available to drift into slabs.    Where are the surprises lurking?   There are isolated slopes in the Southeast Mountains with large fetches that have collected enough drifted snow to form problematic slabs.  Evan was targeting these concerns a few days ago in West Brush Creek without finding a significant problem, but there's a lot of alpine terrain east of town that is difficult for us to access early season, so we have less data. The other surprises are lurking on north and west aspects.  These slopes also share the same horrendous weak layers, but they've been less active because winds have done more eroding than loading.  If you find a drifted slab on those aspects, treat it as guilty.  You'll find those more isolated drifts in midslope concavities or gullies that act as catcher's mitts for drifting snow, such as these gullies on Irwin's West Wall.  

Regions covered