Boletín de aludes

Northwest Mountains

Crested Butte Avalanche Center
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Peligro de aludes

Thu
Alta montaña
3 · Notable
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 3 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

You can encounter dangerous avalanche conditions on well-drifted slopes at upper elevations.  Leeward terrain on the eastern half of the compass is the most likely place to find a sensitive slab of wind-drifted snow.  Avoid terrain with signs of drifting like areas underneath cornices and below ridge tops.  There is a lingering threat of avalanches breaking deep in the snowpack on drifted terrain.  You can reduce your chances of triggering a dangerous avalanche by seeking out sheltered slopes at lower elevations.

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    Up to 8 inches of new snow accumulated Tuesday with a couple more inches possible on Wednesday.  Dangerous Wind Slabs are most likely to be encountered above treeline but can also be found near treeline just not as frequently.  Slopes that have a large, efficient fetch will pose the greatest threat.  Slopes on the east half of the compass are in the bullseye for wind loading.  Use caution and carefully evaluate any terrain with signs of drifting.

    4/1: A wind slab triggered by a cornice fall.  Similar conditions will develop throughout the day on Tuesday.

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely
    Tamaño
    2–3.5

    Large, stubborn slabs several feet thick or more exist over faceted weak layers in the upper snowpack.  The most recent persistent slabs have required larger triggers such as the mass of a smaller avalanche running through the terrain or a cornice falling. The greatest number of avalanches have occurred on easterly-facing slopes where faceted crusts exist. Similar structures exist on west-facing terrain.  Recent warming on lower elevation and more southerly aspects has strengthened the upper snowpack with crusts, and triggering persistent slabs is less likely in that terrain.   Weak layers on north-facing terrain are less developed and have been less active.  

    Early warning signs for this avalanche problem are rare and feedback is infrequent. You can reduce your chance of triggering this avalanche problem by avoiding recently wind-loaded terrain and unusually shallow terrain.  Safer riding is where the snowpack is deep, wind-protected, and on slope angles less than 35 degrees, without steeper slopes above. 

    Very large persistent slab on the east face of Gothic Mountain. 3/31. This avalanche was likely triggered by a cornice falling onto the slope. 

Avalanche Discussion

Storm totals of up to 8 inches exist with the potential for a couple to accumulate on Wednesday.  The deepest totals can be found in the Northwest Mountains with lesser amounts near town and to the east.  Westerly winds efficiently drifted snow at upper elevations on Tuesday but slowly diminished overnight.  The avalanche hazard posed by freshly drifted snow increases as you move toward higher elevations.  There will be more slopes above treeline with sensitive slabs than near treeline as there is more open terrain for the wind to gather snow from and deposit on leeward terrain features.  The difference in the rating between near and above treeline slopes is a product of distribution; the more drifted slopes that exist make it more likely for you to find one.  Simply avoid drifted slopes above treeline and use caution and thoughtful terrain and snowpack assessment near treeline to ensure you do not cross a well-drifted slope.  Drifted slabs are generally isolated below treeline.

There is a lingering chance of triggering an avalanche that breaks much deeper than the storm snow.  This potential is most likely on wind-drifted slopes at upper elevations, more common in the Southeast Mountains, and shallow/rocky terrain.  Several different faceted crusts exist in the snowpack in addition to well-developed Depth Hoar near the ground on northerly slopes with a shallow snowpack (less than 150cm or 5 feet).  The last two storm systems produced several deep and widely-propagating avalanches on well-drifted slopes at upper elevations.  Cornice fall was often the culprit for releasing these deep avalanches.  The current wind-loading period will increase the chance of cornices falling and releasing very large avalanches.  

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