Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The danger will rise throughout the day as the upper snowpack becomes wet. Avalanches will become increasingly likely as the snow surface warms, even on northerly aspects. Warming may increase the potential for failures in buried weak layers, wind slabs, and cornices. Plan to step back from steep terrain and slopes with overhead hazards as you see signs of instability like rollerballs. 

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Rapid warming and light winds will cause the surface snow to thaw. High hazy clouds could cause a greenhouse effect allowing northerly slopes to melt. Wet loose avalanches will be increasingly likely by midday. Areas of unstable wet snow will be more likely where dry, cohesionless snow is getting wet for the first time. Watch for rollerballs and small sluffs from steep, rocky areas 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 lower-angled terrain 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

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–3

    Weak faceted snow and melt-freeze crusts exist at various depths in the upper snowpack. While avalanches are possible in isolated areas, we have seen a decrease in signs of instability. Surface crusts below treeline have made initiating a failure less likely at lower elevations. The majority of avalanches failing on buried weak layers occurred near treeline, which is where snowpack tests continue to show the potential for human triggering. Feedback - like whumpfs and shooting cracks - may be spotty and unreliable. If triggered, persistent slab avalanches can propagate beyond terrain features. They can be triggered from below or from flatter terrain adjacent to steep slopes. You can manage uncertainty by maintaining a healthy distance from convexities, wind-loaded terrain features, and slopes where the upper snowpack is getting wet. Warm temperatures can create stiffer, more sensitive slabs over buried weak layers. Meltwater that percolates down through the snowpack can further weaken old snow. Large natural triggers, like cornice fall, are something to consider if you travel under slopes with big wind lips overhead. 

    (3/31/2023)

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

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Gusty winds and a few inches of snow over the past 24 hours built fresh drifts in leeward terrain. Rapid warming can temporarily increase the sensitivity of already unstable slabs. Specific features of concern include steep slopes below ridgelines, the sidewalls of gullies, and cross-loaded depressions. Watch for blowing snow and cracking in dense, hollow drifts as clues that wind slabs may be unstable in your area. Even small avalanches can have big consequences in extreme terrain or above terrain traps. 

    (4/2/2023)

    Sensitive cornices triggering small wind slabs on the slope below

Avalanche Discussion

Rapid warming and cloud cover can be a weird mix. Avalanches can happen where you wouldn’t normally expect them. Greenhousing can cause wet snow on shady aspects. Freezing levels climbing into the upper elevations for the first time can weaken cornices.

Uncertainty in today's forecast surrounds the sensitivity and distribution of the persistent slab problem, especially in alpine terrain. Faceted grains around crusts in the upper snowpack have been gaining strength in some areas. Snowpack tests near treeline continue to show potential for human-triggering of these facet/crust combos buried 1 to 3 feet below the surface. Surface melt-freeze crusts below treeline have made the problem more isolated at lower elevations. 

As high pressure builds, temperatures and freezing levels will continue to rise. As the surface thaws and water begins to percolate through the upper snowpack, conditions could deteriorate each afternoon and evening over the coming days as variable crusts break down and deep wet snow becomes more widespread. During periods of rapid warming, you can limit your exposure by starting early and retreating from slopes before they get wet and unconsolidated. Plan your days so that have options without overhead hazards during your exit. 

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