Bulletin d’avalanche

Eastside Region

Eastern Sierra Avalanche Center
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Danger d’avalanche

Wed
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

New, dense, wind slabs exist at all elevations and in sheltered terrain features. Watch out for stiff drifted snow over weaker snow. Use extra caution around steep wind-loaded slopes as hard slabs may break in unpredictable ways.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Southwest flow battered windward fetches yesterday and overnight last night. The winds were strong enough to erode hard snowlayers, crusts, and faceted surfaces. The material was re-deposited as hard slabs and wind-board in leeward terrain features at all elevations. Some of these slabs are layered over the weaker snow and may be slow to gain strength. Recent drifting, hollow drum-like snow surfaces, textured surface snow, and shooting cracks are all signs that may indicate unstable wind slabs. 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 strong winds can redistribute snow in surprising ways. It may be possible to find unstable slabs of wind-stiffened snow at lower elevations and in relatively sheltered terrain. These slabs may be triggered from center, bottom or sides of the slope making them less predictable than softer slabs, and harder to escape if caught.

Avalanche Discussion

Recent avalanche activity: As winds picked up over the past 48 hours a series of small human-triggered wind slab avalanches have been reported. On Sunday a skier was caught and carried a short distance in a small wind slab on a steep north-facing slope below a cliff bands at 11,600'. Yesterday at least three small human-triggered wind slab avalanches occurred. These included hard slabs up to 1 foot thick. With increasing mid-slope winds avalanche activity occured at all elevations and in some cases in relatively wind-protected terrain. Two of these slabs were reported as having failed on a layer of soft small near-surface facets at the new/old interface.

Snowpack summary: Mid-snowpack crusts and drought interfaces from the past month have become less concerning and signs of instability within the old snow have decreased. During our most recent period of clear weather melt-freeze crusts developed at the snow surface on all aspects below 8000' and on most aspects except north, northest and northwest at all elevations. Steep northerly terrain developed a 10 to 20cm layer of soft small grained near-surface facets. Below treeline surface hoar was observed at the snow surface in some areas. These surface layers were either damaged/eroded by the past 24 hours of extreme wind or were buried intact by hard wind slabs.

Uncertainty today surrounds the average size and sensitivity of new wind slabs. While there were small to moderate amounts of snow available for transport yesterday, variations in local terrain will contribute to a range of slab thickness. Yesterday, reported slabs did not exceed 25cm thick, or D1.5, but continued to build overnight. Today large (D2) human-triggered hard slab avalanches are possible in isolated areas. Slab sensitivity will be affected by grain types at the new/old interface from 2/26/24. Where slabs overlay persistent grains, they may be reactive and will be slow to gain strength in the coming days.

 

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