Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Copious amounts of loose surface snow and shifting winds have increased concern around fresh wind slab development on all aspects near and above treeline today.  Recent signs of instability on basal facet layers show the continued potential of triggering an avalanche involving the full depth of the snowpack. When in doubt, choosing travel routes with lower slope angles and without overhead hazards will limit your exposure.

Avalanche problems

  • Wind Slabs

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

    Wind slabs will range in size and sensitivity today and may be present on all aspects near and above treeline. Winds over the last 24 hrs outperformed the forecast and have moved around the compass rose. Fresh slab formation was noted in the field yesterday from southwesterly winds. Winds have shifted to the north and increased in speed. Blowing snow, recent drifting, hollow drum-like snow surfaces, and shooting cracks in surface snow are all signs that indicate nearby wind deposits. Be suspect of terrain features that encourage drifting, such as the leeward sides of ridgelines, alpine couloirs, gully features, and cross-loaded depressions. Keep in mind that even a relatively small avalanche breaking in the upper snowpack has the potential to step down to weak layers at the bas of the snowpack and may result in a much larger and more destructive avalanche.

    (2/9/2024)

    Small reactive windslab in the lakes basin 2/9/24

    Photo: Steve Mace

  • Persistent Slabs

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

    Managing our persistent slab problem has gotten more complicated, and the consequences of triggering an avalanche have increased following our most recent storm cycle. Signs of instability, such as shooting cracks and slope scale collapses, have been reported daily in areas with more shallow coverage, specifically in the Bishop area. In areas with a deeper snowpack (near the crest from Mammoth to June), signs of instability may be less obvious. Still, recent field observations have confirmed the continued presence of large and well-developed depth hoar.  In either scenario, a resulting avalanche will likely involve the full depth of the snowpack and may be unsurvivable. While triggering a large persistent slab avalanche will be easier in areas with a generally shallow snowpack, in areas with a deeper snowpack, shallowly buried rocks, trees, and convex rollovers will act as good trigger points. These avalanches can be triggered remotely from adjacent terrain and may propagate long distances and beyond terrain features that typically contain surface instabilities like storm or wind slabs. Traveling on slopes less than 30º without overhead hazards can help you manage this problem today. 

    (2/5/2024)

    Explosive triggered avalanche on Wilson Butte above hwy 395.

Avalanche Discussion

Up until the most recent storm, avalanche hazards in the southern portion of the forecast area were limited by below-average snow depth. The past storm has increased access and use of avalanche terrain from Rock Creek to Bishop Creek. Initial reports from these areas describe a shallow snowpack layered over early-season weak layers. Widespread signs of instability have been reported, such as slope scale collapses and long shooting cracks. Human-triggered persistent slab avalanches are more likely in these areas. Areas along the Sierra crest from Mammoth Lakes north have a more robust snowpack averaging around 2 meters in depth. Recent observations have found that Depth Hoar at the base of the snowpack continues to show a propensity for propagation in stability tests. While triggering an avalanche in these areas has become less likely due to its depth, it remains possible from shallow trigger points. The resulting avalanche may not be survivable. The likelihood of triggering an avalanche at the base of the snowpack varies across terrain from drainage to drainage and, in some cases, within the same slope. Managing persistent slab instability requires extensive snowpack evaluation and deliberate terrain choice. Be careful extrapolating observations from one area to another. Once out in the mountains, signs of instability may or may not be obvious. It may be necessary to probe and dig to check on the presence and depth of buried weak layers. It can be difficult to temper expectations and continue to make conservative choices, particularly when it feels like winter has finally arrived. But this remains the best strategy to limit your exposure. Safer travel options today include sheltered terrain with deeper uniform snow depth, slope angles under 30°, and without overhead hazards.

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