Bollettino valanghe

Eastside Region

Eastern Sierra Avalanche Center
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Pericolo valanghe

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Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Recent human-triggered avalanches and concerning snowpack observations from the past 24 hours highlight the importance of carefully choosing terrain. Be on the lookout for pockets of wind-deposited snow at upper elevations, and continue to track the presence and depth of buried weak layers. Avoiding avalanche terrain in areas where the persistent slab problem exists continues to be the best way to reduce risk.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    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. While triggering a large persistent slab avalanche will be more likely in areas with a generally shallow snowpack, 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 and may propagate long distances and beyond terrain features that typically contain surface instabilities like storm or wind slabs. If triggered the resulting avalanche may involve the full depth and weight of the snowpack. Traveling on slopes less than 30º without overhead hazards can help you manage this problem.

    (2/3/2024)

    A very large persistent slab avalanche on Mt. Laurel. This released naturally with the last 48 hours.

    Photo: Everett Phillips

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Unstable wind slabs may be present on all aspects. Recent drifting, hollow drum-like snow surfaces, and shooting cracks in surface snow are all signs that indicate nearby wind deposits. Low-density surface snow may obscure previously formed wind-slabs in steep north-facing terrain. 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 base of the snowpack and may result in a much larger and more destructive avalanche.

    (2/5/2024)

    Small explosive triggered storm slabs on Wilson Butte above hwy 395.

Avalanche Discussion

Recent avalanche activity: A small human-triggered wind slab avalanche was reported in steep north-facing terrain in the Tuolomne Meadows area yesterday.

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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