Bollettino valanghe

Northwest Mountains

Crested Butte Avalanche Center
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Pericolo valanghe

Fri
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In sintesi

You can trigger a slab avalanche on previously drifted slopes at upper elevations.  Problematic conditions are most likely found below ridgelines, cornices, or behind abrupt changes in terrain shape.  Avoid terrain where you feel a stiff snow surface or see smooth, pillow-shaped deposits.  You will likely trigger small, loose avalanches on steep slopes sheltered from the sun and wind.  Loose snow avalanches can be big enough to knock you down and push you into rocks and trees.  You can manage loose slides through sluff management techniques or choose slopes less than 35 degrees. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    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

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    In terrain that has been protected from the sun and wind, the snowpack is growing increasingly weak and cohesionless.  Weather conditions make human-triggered sluffs larger and more common as the shallow snowpack facets.  These 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 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.  

Avalanche Discussion

Avalanche problems can be found in two different flavors: shallow Persistent Slabs in wind-drifted terrain and loose avalanches in wind-sheltered terrain.  The Persistent Slab problem on wind-loaded slopes presents a greater hazard as the potential size could bury or hurt you.  Over the past week, a string of natural and human-triggered avalanches have been documented on leeward terrain features.  On Wednesday, forecasters experienced cracking and collapsing in stiff, drifted snow along the top of Schuylkill Ridge, which suggests slabs remain sensitive to a person's weight.  Even though slabs are not particularly big, expect them to gouge into the weak snowpack and entrain more mass as they run.  You are more likely to encounter this problem in the Northwest Mountains as more snow has accumulated recently; however, we have far less data from the Southeast Mountains.  Even though the avalanche danger remains LOW at upper elevations in the Southeast Mountains, maintain a sharp eye for signs of slab formation on leeward terrain features.

Sheltered terrain, with soft surfaces and a weak snowpack, presents a loose snow hazard.  The snowpack continues to weaken as it remains shallow and seasonably cold.  Observers have noted triggering loose avalanches on steep, sun/wind-protected slopes that take most of the snowpack out.  The simplest way to manage this problem is through slope angle.  Slopes around 35 degrees or less are unlikely to loose avalanche and likely provide better riding conditions.  As slope angles near or exceed 40 degrees, expect loose snow avalanche to become likely.  Sunny, low-elevation slopes have surface crusts preventing a loose avalanche problem. 

 

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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