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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Highlights

Persistent weak layers in the upper snowpack may still be sensitive to human triggering in isolated locations. Recent avalanches involving these layers failed in surprising ways and evidence of instability was not always obvious in the surrounding area. Wind over the past few days, and warming today add complexity to conditions. High uncertainty means that intentional terrain selection is the best way to calibrate exposure and consequence.

Avalanche problems

  • Loose Wet

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

    An increase in temperatures today combined with light winds and clear skies means that wet snow instability is possible on sunny low elevation slopes. Look out for progressively wetter surface snow on sunny aspects. Rollerballs and pinwheels are the most common signs that the likelihood of wet snow instability is increasing. If these signs are present then it may be a good idea to adjust route selection to avoid passing underneath steep sun baked slopes, especially in confined or cliffy terrain that limits options to escape runouts and could concentrate debris flows.

    (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

    Cold clear nights in the short windows between our most recent storms have created thin sun crusts and weak layers of near surface facets at various depths within the upper snowpack. These are most likely found on 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. Feedback may be limited and avalanches could be triggered suddenly and fail in surprising ways. Remember that persistent slab avalanches can propagate across and beyond terrain features that would otherwise confine surface instabilities and can be remotely triggered from below or adjacent to steep slopes. You can manage uncertainty by reducing exposure and maintaining good terrain margins.

    (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
    1–2

    Hard wind slabs that formed during the past storm are becoming difficult for a rider to trigger, but remain a concern today. Thinner new slabs may have formed yesterday in isolated areas. Expect these to remain reactive today. Be suspect of terrain features that encourage drifting such as the leeward sides of ridgelines, gully features, and cross-loaded depressions. Continually assess patterns in the hardness and depth of the surface snow and the layers immediately beneath. Look for shooting cracks and hollow feeling drifted snow as evidence that wind slabs may be unstable in your area.

    (3/31/2023)

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

Avalanche Discussion

Uncertainty in today's forecast surrounds the sensitivity of the persistent slab problem. As recently as three days ago stabilty tests indicated that this layer was still primed for human triggering and capable of propagating across slopes. During this week's mild weather we expect these layers to slowly gain strength, but the isolated nature of the problem means that it will be difficult to track and measure improvement in stability.

The last confirmed avalanche on the 3/19 and 3/29 near-surface facet layers was reported on 3/31 - six days ago. However, avalanches that released during the wind event on 4/2 and 4/3 broke in surprising ways. Wide propagation and remote triggers suggest these avalanches may have involved buried persistent weak layers.

Warming will be a factor in the upcoming days and wet loose avalanche activity may provide a larger trigger for weaknesses in the upper snowpack. Use caution around slopes that are becoming wet as the winter snowpack begins its transition.

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