Boletín de aludes

Southeast Mountains

Crested Butte Avalanche Center
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Peligro de aludes

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

Lo esencial

Dangerous avalanche conditions have developed as 24hr snow totals have stacked up. Storm slab avalanches are going to become reactive to human triggers like flipping on a light switch as they are building on a weak old snow surface. In some terrain that switch has already flipped, and in other areas that avalanche problem is just waiting for a little more snow to accumulate. Either way, you don't want to be in the wrong terrain when you find out how reactive this avalanche problem is. Start your day with lower consequence terrain and small test slopes, while further planning to set a limit on how aggressive you plan to get with your terrain selection. 

Problemas de aludes

  • Storm Slabs

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

    In the last 24 hours, around 6 to 10" of new snow has accumulated. This snow has come with some low water content and is looking surprisingly low-density. The potential blower conditions may be a bit deceiving. This snow is accumulating on a weak old snow surface, and once it reaches its tipping point, these soft slabs will start to exhibit persistent slab characteristics with the potential for remote triggering and wide propagation. There are collapsible crusts on easterly and westerly facing slopes and near surface facets on northerly facing slopes. Due south-facing slopes having thicker crusts and storm slabs will be slower to develop in those areas. Additionally, there is a lot of snow available for entrainment, and a triggered sluff or slab avalanche will quickly grow in size as it runs down sustained steep slopes. 

    Look for feedback, such as shooting cracks, on small, steep test slopes. This avalanche problem may not be reactive until you reach slope angles over 35 degrees. 

    Small, steep test slopes can help identify unstable Storm Slabs. 

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    There are several faceted weak layers in the snowpack that remain a concern in some terrain. The most concerning slopes include those that held an unusually shallow and weak snowpack prior to our March storms (like Round Mountain), where snow depths are currently less than about 5 feet (150cm) deep, or in wind-effected terrain with variable snow depths (like Teo or Carbonate Hill).  There are also recently buried faceted crusts in the upper snowpack on easterly and westerly-facing slopes that are just developing an issue (like Whetstone). Carefully assess the snowpack structure and give yourself a margin for error in handling this problem. There is a high degree of variability across the region and on different aspects.  Choose simpler terrain when in doubt. 

     

Avalanche Discussion

On Tuesday we are in a lull between storms before the avalanche danger continues to ramp up this afternoon and through Wednesday. This is our 3rd atmospheric river event this month and avalanche conditions are going to develop differently than during the previous two storms. During this round, the storm snow is accumulating on a weak old snow surface. More like what we would see in December for example. Given the low density of the current storm snow, you may observe more sluffing than slab activity in lower-elevation wind-sheltered terrain. However, at some point, the light switch will flip and storm slabs will become reactive on that old snow surface. That switch will get flipped at different times across the forecast area and you don't want to get caught in the wrong terrain when that happens. 

Accumulating snow starts picking up around mid-day or this afternoon. Avalanche conditions will continue to change during that time and the avalanche danger will continue to rise. On Wednesday, an extreme wind event combines with high precipitation rates, and the avalanche danger is expected to rise to HIGH (4 of 5).

It's been a rough weekend for our backcountry community. Persistent slab issues have caught numerous groups by surprise this week in the Elk Mountains, and unfortunately, two of the accidents resulted in fatal outcomes. One accident was near Marble and the other near Aspen Highlands.  In the deeper zone, the issues appear to be tied to a near-crust faceted layer at the base of our two recent storms (March 10th interface), about 2 to 3 feet deep on average.  Our forecast team checked out the impressive crown on Mt. Baldy,  which was notably thicker due to extensive wind drifting.  This issue has been particularly challenging to forecast for because the layer was not obvious on the snow surface prior to its burial, so we don't have a clear map of its distribution.  Furthermore, it has provided very limited feedback in the way of collapses or unstable pit results.  Our best tool right now for plotting the problem is observing avalanche activity patterns, which have been most common on east-to-south aspects.  With significant loading over the next few days, we are in a stepping-back mindset, with more uncertainty on where and when this problem will act up again.  In our shallower zone, we are painting a broader distribution because we are also concerned about issues on northerly terrain where the snowpack is shallow and/or variable in depth.  Sunday's accident in Maroon Bowl is a good example of that.

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