Lawinenlagebericht

Northwest Mountains

Crested Butte Avalanche Center
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Lawinengefahr

Mon
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 these large collapses below Schuylkill Peak yesterday.  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

Booming collapses yesterday below Schuylkill Peak (video) and a skier-triggered slab on Friday on Mt. Tilton provide clear evidence that the hard slabs formed during the past two weeks of windy weather remain a concern.  Check out our weekly snowpack summaries for a recap on the weather events and snowpack history that got us to this point.   Our forecast team has consistently gotten feedback targeting the persistent problem in the past week because the most problematic slopes are fairly recognizable: smooth, hard, and occasionally thick drifts formed in terrain features that catch the snow as it blows across the terrain.  With a careful eye for recognizing wind drifting patterns, there are plenty of options to travel through the terrain without encountering our current slab problem.  Slopes that have seen wind erosion (featuring rippled sastrugi) or southerly aspects lacking the underlying weak layer are the safest options for traveling at higher elevations. 

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. 

Events:  Our first Fireside Chat of the year is today (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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