Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

Stay cautious of previously drifted hard slabs below leeward ridgelines, rollovers, and in concave gullies, demonstrated by large collapses below Schuylkill Peak and a triggered slide on Mt. Emmons over the weekend.  Look for softer, less wind-affected snow to avoid the problem.  Small sluffs entraining most of the snowpack are easily triggered in wind-protected, shady slopes steeper than 35 degrees.  

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Since 12/9, several northwest-to-southwest wind events formed slabs around a foot thick or more in heavily wind-loaded terrain features. These wind-drifted slabs are most commonly found at higher elevations below leeward ridgelines and rollovers on east to 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 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, especially in high-consequence terrain. 

    A booming collapse and shooting cracks triggered on 12/21 on this heavily drifted slope demonstrate the potential to trigger a hard, persistent slab avalanche.  

  • Loose Dry

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–1.5

    In terrain that has been protected from the sun and wind, most commonly below treeline on the north to east aspects, the snowpack is weak and cohesionless.  In these areas, you can easily trigger dry loose avalanches in terrain steeper than 35 degrees.  Point-release instabilities are relatively small and easy to recognize. Still, they can spell trouble by pushing you into trees, rocks, or gullies, especially in long, steep terrain where they will gouge to the ground and gain more volume.  Use sluff management techniques or move to less consequential, lower slope angles to manage the problem. 

Avalanche Discussion

The latest in our steady trickle of feedback from our persistent slab problem comes from Mt. Emmons yesterday, right on the boundary between our two forecast zones.   The second rider to cross a wind-loaded feature on the far looker's left side of Red Lady Bowl popped a hard slab that broke 1 or 2 feet deep near the ground.  Although our slab issues are localized to previously wind-loaded terrain features, like a wind slab, we've been calling it a persistent slab due to its unusually prolonged period of instability. A hybrid problem, if you will. These slabs started forming two weeks ago from multiple wind drifting events over the very weak facets left behind in old bed surfaces or shallow snowpacks from our December drought.  Other recent feedback includes booming collapses on Saturday below Schuylkill Peak (video) and a skier-triggered slab on Friday on Mt. Tilton.   

Where the snow surface is soft, sugary, and protected from wind effects (most commonly below 11,000' on the north half of the compass), the snowpack lacks any slab concerns as it continues to facet and weaken.  In both zones, observers report dry loose avalanches (aka facet sluffs) picking up momentum and gouging to the ground once they get moving (ex. Snodgrass, Schuylkill Ridge, Axtell, Emmons). Two people have been caught and carried in dry loose avalanches near Marble, one earlier this month and one on Friday.   Sluffs aren't a concern where the snow surface is stiff from wind (generally at higher, more exposed terrain) or sun crusts (south to west aspects) or on slope angles less than 35 degrees. 

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