Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

Thu
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Out of date — this forecast expired 3 years ago.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

You could trigger a wind slab avalanche on leeward slopes where blowing snow builds rounded, rippled drifts. More destructive avalanches are possible in areas where a shallower or variable snowpack covers persistent weak layers. Plan to step back to lower slope angles with minimal overhead hazards as the incoming storm begins to load steep terrain.

Avalanche problems

  • Wind Slabs

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

    The likelihood of triggering a wind slab avalanche will increase throughout the day. Recently formed drifts can still be sensitive where they rest atop weak, sugary snow. Look for snow blowing onto steep open slopes. Use caution around terrain features that encourage drifting. You’re most likely to trigger a stiffened slab of wind-textured snow on the leeward sides of ridgelines or the sidewalls of couloirs and gullies. You can look for shooting cracks on small test slopes to understand how slabs may behave in bigger terrain. As new snow falls and the hazard increases late this afternoon, you can avoid the problem by riding softer snow on sheltered slopes. A relatively small avalanche breaking in the upper snowpack has the potential to step down to buried weak layers and may result in a much more destructive avalanche.

    (2/7/2024)

    Skier triggered windslab, June BC

  • Persistent Slabs

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

    As new snow and wind begin to load shady slopes later today, the chances of avalanches breaking deeper in the snowpack will increase. Until then, you could still trigger a large persistent slab avalanche in areas with a generally shallow snowpack. The most recent signs of instability - shooting cracks and collapsing - from buried weak layers have been reported in the mountains around Bishop. In areas with a deeper snowpack, shallowly buried rocks, trees, and convex rollovers can act as trigger points. Persistent slab avalanches can be triggered remotely from flat terrain below or adjacent to steeper slopes. They can propagate widely, connecting multiple start zones. Breaking cornices or smaller wind slab avalanches may be enough to set off an avalanche involving the full depth of the snowpack. If you decide to step out into more consequential terrain, you can stack the deck in your favor by riding planar or concave slopes with a deep, uniform snowpack. Plan to step back as new snow falls. Traveling on slopes less than 30º without overhead hazards is the most effective strategy for reducing risk.

    Large persistent slab avalanches in Mammoth Rock Bowl and near the Poop Chute that failed naturally overnight on 2/4.

    Photo: Steve Mace

Avalanche Discussion

When new snow falls this afternoon, and is drifted onto leeward slopes, it will land on a variety of surfaces. There are melt-freeze crusts at lower elevations and on sunny aspects. Ridgelines at all elevations have denser wind-affected snow. On northerly slopes, near-surface facets could make new wind slabs extra sensitive. So far this season, storms similar to the one that will move into the area today, with about a foot of snow and strong wind, have produced very large natural avalanches breaking in old snow near the ground. Natural avalanches initiating in rocky alpine start zones could occur tonight and tomorrow. Even before new snow begins to fall, people could trigger persistent slab avalanches where the snowpack is generally thin.

The likelihood of triggering an avalanche at the base of the snowpack varies between drainages and, in some cases, across the same slope. In wind-battered alpine terrain, there is a high amount of uncertainty over the distribution of weak layers. At lower elevations, weak snow under a slab is most likely on shady, open slopes with smooth ground cover. The persistent slab structure is most consistent near treeline and mid-slope.

Coverage since early February has increased, and so has access to avalanche terrain from Convict Lake to Bishop Creek. Cracking and collapsing were reported in the southern end of the forecast area through the 8th. While signs of instability have decreased, human-triggered persistent slab avalanches are more likely in these areas.

As the danger rises with new snow and wind, plan to step back and give slopes harboring persistent weak layers a wider berth until they can adjust to the new load. 

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