Avalanche forecast

Northwest Mountains

Crested Butte Avalanche Center
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Avalanche danger

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

Several natural and human-triggered avalanches reported yesterday showcase the potential to trigger a slab avalanche about a foot deep in wind-drifted terrain or sluffing in wind-protected terrain.  Continued snowfall and windloading last night are contributing to ongoing instabilities.  Safer riding is on southerly aspects, lower elevations, or in smaller, less consequential 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 out of modest amounts of snow available for transport. These wind-drifted slabs are most commonly found at higher elevations below leeward ridgelines and rollovers on east-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 sometimes hard and difficult to trigger, but some formed over weak, faceted snow that is slow to heal, making for variable feedback.  Assess recent wind loading patterns and consider avoiding previously wind-loaded terrain features in high-consequence terrain, especially where slabs are harder and thicker, making them difficult to manage.   

    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 that occurred in late November. 

     

     

    A remotely triggered slab avalanche about 8" to 12" thick on Purple Ridge.

    12/14/2024

  • Loose Dry

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

    In terrain that has been protected from the sun and wind this week, the snowpack is growing increasingly weak and cohesionless, and human triggered sluffs are becoming larger and 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

Thank you to everyone who submitted observations yesterday helping us dial in patterns following a tricky forecast week featuring small amounts of snow, bigger amounts of wind, and a fragile snowpack that is simply eager to fall apart whenever the snowguns turn on. In the meantime, we're dancing between Low and Moderate danger due to the relatively shallow instabilities driven by the small storm systems this week.    Our weekly snowpack summary has all the details of how we got here.  We can simplify our rotten snowpack into two categories: wind-protected terrain vs. wind-affected terrain. 

Wind-protected terrain: On shadier aspects, the snowpack is weak, faceted, and generally lacks a slab.  You can get small dry loose avalanches moving in terrain steeper than about 37 degrees that gouge into the weak facets (aka facet sluffs). The deeper you are sinking into the sandbox of facets, and the longer the terrain feature, the larger the point release will get.  This dry loose avalanche off of Schuylkill Ridge exemplifies the issue.  Facet sluffs can surprise people because they start slow and tiny but eventually gain volume and speed and smack you in the back right about the time you think to yourself, "No sluffing here."  Good communication with your partners, such as radios, and sluff awareness can help you manage the problem.

Wind-affected terrain: Multiple generations of wind drifting this week have formed relatively shallow slabs littered across the terrain favored by northwest shifting to southwest winds. The slab avalanche patterns observed this week summarize the situation well: wind loaded slopes over fragile weak layers on colder aspects have been most active (most commonly on N to E, less commonly on N to W, up to D1.5 so far and potentially increasing to D2 overnight in the NW Mtns with additional snow and windloading).  Now that we are stacking multiple generations of snow and wind drifting on a persistent weak layer, we're calling the problem a persistent slab, though in some cases, you can manage it like a wind slab.  Feedback is variable: in areas gently affected by winds, it's soft and easy to manage, while in wind-blasted areas, it's a harder slab that's less predictable with fickle feedback.  For example, this observation yesterday noted a lack of signs of instability before the remote-triggered slab on Purple Ridge.  

Both forecast zones are dealing with the same situation. However, the danger is higher in the snow-favored Northwest Mountains because the issues described above are generally larger and more common. The Northwest Mountains have picked up significantly more snow in the past week (upwards of 12" to 18" in some areas, in contrast to just a few inches in the Southeast Mountains). Thus, in the deep zone, more snow has been available for transport, and more snow is now entrained by these slabs in motion or triggered sluffs.  

Regions covered