Boletín de aludes

Northwest Mountains

Crested Butte Avalanche Center
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Peligro de aludes

Sat
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 7 months ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Wind-drifted terrain at upper elevations represents the most probable place to trigger a slab avalanche.  Leeward easterly and southerly slopes received the most loading last weekend, but you might find cross-loaded features on other aspects and at lower elevations.  Stiffer snow below ridgelines or cornices, and in cross-loaded gullies, indicates that you have potentially found the problem. You can reduce your risk by avoiding previously drifted terrain or by choosing wind-protected slopes at lower elevations.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1.5–2.5

    Most avalanche concerns today involve slabs of drifted snow that formed over the facets and faceted crusts from our January drought.  These slabs, up to several feet thick, could remain sensitive to human triggers on some leeward terrain features, most commonly on east to south-facing aspects at higher elevations and on crossloaded features elsewhere.  Because these recent slabs formed on highly variable snow surfaces, expect hit-or-miss feedback as you move through the terrain.  Collapses and shooting cracks are clear red flags. There is isolated potential for a slab failing in the upper snowpack to step down and trigger a deeper, harder avalanche near the ground. The most reliable way to manage this problem is conservative terrain selection—sticking to slopes under 30° or small terrain features without terrain traps.   Lower-elevation southerly aspects offer the safest snowpack, and slabs are typically less developed in wind-protected or wind-eroded terrain.

    Several large avalanches that failed on windloaded southeast-facing slopes over the weekend.  

Avalanche Discussion

The avalanche danger is on a gradual downtrend after last weekend's loading event and natural avalanche cycle.  However, forecasters have experienced collapsing while traveling in near and above treeline terrain, often on easterly and southerly aspects (Galena, Wolverine Basin).  Weak snow is common beneath last weekend's storm, but prevailing winds from the northwest preferentially loaded easterly and southerly aspects.  The avalanche activity rose highlights this pattern of increased avalanche activity on wind-drifted easterly and southerly terrain.  You should expect to find drifted slabs on westerly and northerly aspects, but less frequently, and often due to crossloading.  The avalanche activity and signs of instability suggest a cautious approach to terrain with evidence of previous drifting.  This video shares more information about the concerning structure Zach encountered in Rock Creek while investigating a natural avalanche.

Without the additional stress from windloading, the snow that fell last weekend seems to have found equilibrium with the fragile facets below.  The avalanche danger rating is LOW below treeline in both forecast zones. However, be aware of two potential issues.  Previous winds formed drifts on isolated features at lower elevations, so you could trigger a slab avalanche if you found one of these isolated drifts.  Secondly, some low elevation terrain is capable of Dry Loose avalanches (facet sluffs) on steep slopes with an entirely faceted snowpack.   This structure is most common on the northern half of the compass.  Forecasters recently triggered a few facet sluffs (1,2) on steep, northerly terrain at low elevations.

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