Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 2 years ago.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

Highlights

Last weekend, both human-triggered and natural slab avalanches occurred. These slab avalanche concerns are specific to wind-loaded terrain, such as below ridgelines or in concave terrain features. The primary concern in wind-sheltered areas is dry loose avalanches in steep terrain that has a soft snow surface.

Avalanche problems

  • Persistent Slabs

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

    Since 12/9, 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 consider avoiding previously wind-loaded terrain features, especially in high-consequence terrain.   

     

     

  • 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. These conditions are leading to human-triggered sluffs 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

On Monday night and into Tuesday, elevated southwest winds moved back through the forecast area. 12,000ft weather stations recorded average wind speeds in the 30's with gusts into the 60's. A period of moderate winds also moved through lower valley elevations with gusts into the 20's. These winds blew what little snow was left to transport and mostly continued to harden snow surfaces in wind-exposed areas. Unfortunately, those valley winds may have also worked into a few more previously wind-sheltered areas and perhaps decreased the riding quality of those snow surfaces. As snow surfaces harden, the persistent slab avalanche problem will continue to become more stubborn to trigger in more locations. There may also be a few new hard slabs that formed in those lower elevation areas that were exposed to those valley winds. These winds didn't otherwise dramatically change avalanche conditions and were more of a kidney punch to a snowpack suffering from an extended period of drought. The snow water equivalent of the Gunnison River basin was once over 150% of the median back around Thanksgiving, and it has since declined to 104% of the median. We will continue to see that number decline until we get back into some more notable winter storms.

Looking at the slab avalanche patterns since our first in a series of wind events started on 12/9, 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 before receiving the brunt of wind loading.  Snowfall has also significantly favored the NW Mountains, 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.  A forecaster was targeting these concerns last week 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 west and north 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.  

The dry loose avalanche problem will likely be with us for an extended period. This avalanche problem typically occurs in our area when we are stuck in these long drought periods with cold valley inversions and little accumulating snow. This setup promotes faceting in the snowpack and creates more cohesionless snow available for entrainment by those sluffs. Slope angles must be steep for this avalanche problem to occur often in the upper 30-degree range. In some places across our forecast area, this avalanche problem may exist, but there isn't enough snow to travel on those slopes without riding on the ground. That setup is more common in the Southeast Mountain forecast area. In the NW Mountains, there is more commonly enough snow to ski and ride where this avalanche problem exists, so backcountry travelers could encounter this avalanche problem more often. 

Events:  Our first Fireside Chat of the year is this Sunday (12/22) at 6 p.m. at the Eldo.  Andy Sovick(Beacon Guidebooks/OnX Maps) will chat about Maps and Tour Planning.  These events are free and open to all.

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