Bollettino valanghe

Eastside Region

Eastern Sierra Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Signs of instability have become less obvious. Buried weak layers continue to show the potential for large avalanches and warrant a cautious approach to avalanche terrain. Travel routes with lower slope angles and without steep slopes overhead are good options to reduce risk.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–3

    Persistent slab avalanches can be triggered from a distance on flatter terrain adjacent to, or below steep slopes. They often propagate long distances, connecting terrain features that typically contain surface instabilities such as storm or wind slabs. If triggered, the resulting avalanche could break with little warning, involving the full depth of the snowpack.  Where weak layers are buried more than three feet below the snow surface signs of instability may be less obvious, but the possibility of human-triggered avalanches still exists. Cautious route selection remains the most important strategy to manage this problem. Choosing travel routes with lower slope angles and no overhead hazard is a good way to limit your exposure to these types of avalanches.

    Large remotely triggered avalanche. North side of Dunderberg - N/NE Aspect 10400'

    Photo: High Sierra Snowcat

  • Wind Slabs

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

    Wind slabs that formed over the past two days have gained strength but may still be sensitive to human triggers. Be suspect of terrain features that encourage drifting, such as the leeward sides of ridgelines, alpine couloirs, gully features, and cross-loaded depressions. Look out for strong wind-drifted snow layered over softer snow in the upper snowpack. Hollow feeling slabs and shooting cracks in the snow surface are signs that wind slabs may be unstable in nearby terrain. It is critical to remember that the distribution of wind slabs overlaps with our persistent slab problem. This means that even a relatively small avalanche breaking in the upper snowpack has the potential to step down into older snow, creating a much larger and more destructive avalanche. 

Avalanche Discussion

Recent avalanche activity: On Wednesday 1/24/24 a few inches of snowfall combined with blowing snow brought on a round avalanche activity involving wind-deposited snow and buried weak layers lower in the snowpack. Wind slab avalanches up to D2 were reported in the Sherwins, the Mammoth Lakes basin, and in the northern portion of the zone along 395 to Lee Vining. Persistent slab avalanches were spotted in North and Northeast facing alpine terrain on Bloody Mountain, Mt. Gibs, Mt. Wood, and in the Mount Dana area. No new natural or human-triggered avalanches were reported yesterday.

Snowpack discussion: Cohesive surface slabs a few inches to a foot thick formed on leeward slopes near and above the treeline on 1/24/24. No new wind slab avalanches were reported yesterday.  Recent observations found non-persistent grains at the interface below the surface slab, but the layer did show propagation propensity in extended column tests. On most aspects and at all elevations, a layer of depth hoar and basal facets that formed in late Nov. and early Dec. is buried between 2 and 3.5 feet below the snow surface under a strong mid-pack slab. Signs of instability have become less obvious where basal weak layers are buried more than 3 feet deep. However, variations in snow depth between drainages and within slopes continue to make the likelihood of persistent slab avalanches difficult to assess. Two snow profiles taken from the same slope in Virginia Creek (see attached media) are a good illustration of spatial variability in the snowpack structure and stability test results.

Forecasting persistent slab avalanche activity is inherently uncertain. This problem exists in most areas where there is enough snow for riding. The most effective risk management strategy for this hazard is to be patient and avoid steep terrain.

 

 

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