Boletín de aludes

Eastside Region

Eastern Sierra Avalanche Center
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Peligro de aludes

Mon
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
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

Large human-triggered avalanches are possible today. Buried weak layers have recently produced avalanches that release with little warning. Blowing snow means that sensitive drifts could be forming in your area. Limiting your exposure to overhead hazards, convexities, and slopes with drifted snow is a good way to manage overlapping problems. Shady slopes are a safer alternative to steep sunny terrain with wet snow. 

Problemas de aludes

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2.5

    The spring sun is high in the sky and temperatures will again climb above freezing. Wet loose avalanches will be possible by midday. In areas where the sky is clearest, winds are lightest, and freezing levels rise near 10,000 feet, areas of unstable wet snow will be more likely. At lower elevations, slopes with a slight northerly tilt have been getting wet for the first time. Watch for rollerballs and small sluffs on sunny slopes as the first sign that wet loose avalanches are becoming a hazard. Rocky chutes, vegetated slopes, and areas with shallow snow cover will be the most concerning. Watch your overhead hazards and move to shady slopes if the surface snow thaws causing you to sink into deep wet snow. 

    (4/1/2023)

    Small wet loose avalanche that ran above Mono Lake on 4/1/23

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1.5–3

    Cold clear nights in the short windows between storms in late March created crusts and weak layers of near-surface facets at various depths within the upper snowpack. These are most likely found on isolated slopes that combine sun exposure and wind loading. A stabilizing trend in the weather and settling surface snow may give a false sense of stability. Warm temperatures can create stiffer, more sensitive slabs over buried weak layers. Meltwater that percolates down through the snowpack can further weaken already weak snow. Feedback may be limited and many recent avalanches have been triggered remotely without prior warning. Persistent slab avalanches can propagate beyond terrain features and connect several start zones. They can be triggered from below or from adjacent slopes. You can manage uncertainty by maintaining a healthy distance from convexities, wind-loaded terrain features, and suspect slopes. 

    (3/31/2023)

    Large remote triggered avalacnhe in V-Bowl, Lee Vining area, 9000' BTL, 3/31/23

  • Wind Slabs

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

    Extreme winds could strip whatever snow remains available from windward slopes and add to wind slabs recently deposited in steep leeward terrain. These will be larger the higher you climb. Specific features of concern include steep slopes below ridgelines, the sidewalls of gullies, and cross-loaded depressions. Watch for blowing snow, recent avalanche activity, and cracking in dense, hollow drifts as clues that wind slabs may be unstable in your area. If triggered, hard slabs could propagate widely or break above you. You could avoid the problem, and find soft snow, in sheltered terrain.

    (3/31/2023)

    Small natural avalanche in Redcone bowl triggered by direct wind loading. 3/31/23. N, 10,300'.

Avalanche Discussion

Overlapping and diverse avalanche problems could make hazard assessments challenging today.

  • It will be warm and mostly sunny again today. Yesterday, 4/1, larger-than-expected wet snow avalanches ran at lower elevations on Mt. Tom. Rollerballs were reported on shady aspects of the Chicken Wing. But, a good refreeze overnight and strong winds today could limit new wet snow instability.
  • Winds were strong yesterday and overnight with blowing snow reported over the Sierra Crest, especially near Bishop Pass and from Crowley to Mammoth. Upwind slopes have likely been stripped, leaving less snow available for transport. Extreme winds are in the forecast today, so some new slab development is expected.
  • Skiers remotely triggered a large slab avalanche at 9000 feet on an east aspect in V Bowl Friday, 3/31. It likely failed on a crust/facet combo buried on March 29th. This is the most recent in a series of natural and rider-triggered slides failing on weak old snow atop crusts. Most of the activity has been concentrated near treeline on southeast, east, and northeast aspects. Many of these have been triggered from adjacent slopes. On the 29th, a very large natural avalanche released mid-storm on a northwest aspect at 11,400 feet on Bloody Mountain. The crown appears to connect around multiple terrain features. This avalanche also likely failed within the old snow.
  • Crust/facet combinations exist on west through north through southeast aspects at all elevations. The upper layer is typically 20 to 40 cm below the surface and the older layer (buried 3/19) is between 70 cm and more than a meter deep. Slabs releasing on these interfaces have most often been wind-deposited. There are high levels of uncertainty surrounding these layers because they have given inconsistent feedback, even on slopes adjacent to remotely-triggered avalanches. Wetting of the upper snowpack could further weaken old snow.

So, it will be important to do your own localized assessments as you move through the mountains today. Keep an eye out for blowing snow and monitor surfaces closely for signs of warming.  Wide safety margins, like low slope angles and simple terrain choice, are the best defense for managing uncertainty.

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