Boletín de aludes

Eastside Region

Eastern Sierra Avalanche Center
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Peligro de aludes

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

Lo esencial

Winds have drifted loose surface snow and created dangerous avalanche conditions. Adding complexity to the picture are persistent weak layers. These are buried deep enough to result in inconsistent feedback, but if triggered, the resulting avalanches will likely be very large and destructive. Low slope angles and simple terrain without overhead hazards are critical strategies to minimize your exposure.

Problemas de aludes

  • Wind Slabs

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

    Though snowfall has ended, strong and shifting winds have distributed dense, rounded slabs across multiple aspects. Expect the largest and most concerning deposits below ridgelines and in cross-loaded gullies near and above treeline. Slabs likely developed downwind of tree fences and other features that promote drifting at lower elevations during yesterday’s wind event. Recent natural avalanche activity is a clue that human-triggered slides are still likely. Sheltered terrain and low slope angles are the best strategies to avoid dangerously large wind slabs that can propagate across start zones. Be wary of steep, wind-loaded slopes above you. 

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2.5–3.5

    Though snowfall has ended and winds have decreased, we are entering a dangerous period with high levels of uncertainty. While the sheer weight of our new snow may have been enough to overwhelm buried weak layers in some areas, in others, things may be hanging in the balance. The weight of a rider, a relatively small wind slab avalanche or a cornice fall may be all that is needed to trigger a large and destructive avalanche. Persistent slab avalanches often propagate across terrain features and can be triggered from a distance. The best management strategy is to put a wide margin between yourself and the terrain where the problem may exist. When in doubt avoid being on or underneath slopes greater than 30° in steepness.

    Very large persistent slab avalanche on Mt. Tom observed during a brief break in the recent storm cycle.

  • Loose Wet

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

    Temperatures are forecast to climb above freezing this afternoon below about 9500 feet and the sun will be out for the first time in days. Cold, low-density snow could become wet for the first time. Watch for rollerballs and small sluffs on solar aspects as the first sign that wet loose avalanches are becoming possible. Rocky chutes, vegetated slopes, and areas with shallow snow cover will be the areas of greatest concern, particularly at lower elevations. Plan your day to be out from under very steep sunny slopes if the surface thaws. 

Avalanche Discussion

An extraordinary storm cycle exited the region yesterday and extraordinary avalanche activity has been recorded. Large to very large avalanches were reported every day since February 23rd. Winds shifted to the north yesterday obscuring the mountains with intense blowing snow. Forecasters triggered small wind slab avalanches and shooting cracks near and below treeline in Bishop Creek. 

Some of the larger reported avalanches have propagated across whole terrain features or were triggered remotely. These failed on faceted layers that ESAC staff tracked in detail before the start of the cycle. These layers are buried under the storm snow from the past 8 days, meaning that they may not give clear feedback until they propagate across the slope resulting in unexpectedly large and destructive slides. Usual "safe routes" should be carefully re-evaluated for exposure to overhead hazards.

Temperatures will recover quickly from overnight lows below zero to above freezing by early afternoon. With sunny skies, freezing levels reaching nearly 9500 feet, loose dry surface snow may become wet for the first time. 

Besides complex and overlapping avalanche hazards, the recent storm cycle has hampered travel on roads and highways. Some communities are without power. Some neighborhoods have been evacuated. Keep emergency response times in mind as you consider your level of acceptable risk today. 

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