Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

Thu
Alpine
4 · High
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Strong winds are building wind slabs on leeward terrain features at upper elevations. Avoid large avalanche paths where there is a high likelihood of triggering a dangerous avalanche.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3

    Over 20 inches of new snow combined with strong winds will continue to build fresh wind slabs today. Wind slabs are most commonly found on the leeward side of terrain features that block or re-direct winds. Today these areas are most likely just below ridge lines and in sheltered areas near and above treeline that collect wind-drifted snow.  The hardness of wind-deposited snow means that wind slabs may be triggered from low on the slope or from areas you might consider "safe spots". If triggered expect these avalanches to propagate across start zones. Snow plumes along ridgelines and blowing snow along the snow surface are good indications that new wind slabs are building in your area.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Prior to the most recent storm, no avalanches had been reported on the 12/01 PWL in over a week. During that time the snowpack gained strength and the problem became more isolated. With the most recent round of loading uncertainty over the distribution and sensitivity of this problem has returned. A relatively small wind slab avalanche or the weight of a skier might be all that is needed to trigger a large destructive avalanche. Persistent slab avalanches can be remotely triggered from adjacent slopes and flat terrain below a steep slope, and if triggered, can propagate across and around terrain features that would otherwise confine new snow instabilities. This problem is most likely in complex terrain near and above treeline, on steep and unsupported slopes, in areas with shallow trigger points, and in areas with a generally thinner snowpack. There is high uncertainty with this problem following the storm so the best management strategy is to put a wide terrain margin between yourself and terrain where the problem may exist.

Avalanche Discussion

Although precipitation, wind, and temperatures decreased overnight danger is High for the above-treeline elevation today due to the high likelihood of large human-triggered wind slab avalanches. Uncertainty is high with regard to the Persistent Slab problem. The snowpack was saturated with rainwater below ~ 8000' yesterday, and whumpfs and cracks indicated that percolating water had weakened the 12/01 layer.  Above that elevation, the lower snowpack is moist or dry, but there is a defined layer of wet snow at the base of the recent storm snow up to 10000' at least. As the wet layer refreezes it may become harder to trigger the PWL at lower elevations. Without many observations from mid-storm, we will have to wait for clear skies today to see whether there has been recent avalanche activity on this layer. More information is needed as we reassess the distribution and sensitivity of persistent slab problem.

Regions covered