Bollettino valanghe

Eastside Region

Eastern Sierra Avalanche Center
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Pericolo valanghe

Sun
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
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In sintesi

Wind loading and periods of heavy snowfall will keep avalanche danger elevated. Very large natural avalanches are likely today. Travel in and below avalanche terrain is not recommended. Avoid the runouts of large avalanche paths with leeward start zones.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Certain
    Dimensione
    2–3.5

    Strong to extreme SW winds, combined with abundant dry snow at higher elevations, are forming cohesive layers of wind-deposited snow in leeward terrain features. Wind-deposited snow accumulates more quickly than direct snowfall alone meaning that wind slabs in large start zones below ridgelines, or in cross-loaded terrain features may be many times larger than the amount of snowfall measured at weather stations. Wind slabs in leeward avalanche paths may run farther than expected due to better-than-usual coverage in tracks, especially at lower elevations.

    A very large explosive triggered wind slab avalanche from 2017. With today's snowfall and wind avalanches like this may release naturally.

    Photo: Matt Irons

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1.5–2.5

    Storm slabs form during periods of intense precipitation when a cohesive layer of dense snow does not bond well to the layer below. Storm slabs can release at the interface between the new and old snow, or on a layer within the storm snow. With up to 30" of new snow in the past 24 hours, and snowfall rates over 3" per hour, these avalanches could be large today. In mountain towns, be aware of small steep slopes like road cuts, snowbanks, and roofs especially when they end in confined areas where snow can pile up.

    (3/10/2023)

    Slab avalanche in the Town of Mammoth Lakes

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2.5–4

    Deep persistent slabs are a difficult problem to assess, predict and manage. Deep slab instability likely peaked yesterday during periods of rapid loading and warming, however, continued wind loading today and the high likelihood of wind slab avalanches means that large triggers are still present and avalanches could break on weak layers deeper in the snowpack. With good coverage in the tracks of avalanche paths at all elevations, these avalanches could reach maximum runouts and impact areas like mature forests and flat terrain usually considered to be safe zones.

Avalanche Discussion

Widespread natural avalanche activity was observed yesterday where visibility permitted. Multiple storm slabs and roof avalanches were reported in mountain communities yesterday.

Snow levels are forecasted to remain below 8000' today, so rain on snow should be less than yesterday. If snow levels rise higher than expected, wet slab and wet loose activity may result. Rising temperatures and rain on snow may increase the likelihood of roof avalanches in mountain communities.

This storm continues to have major impacts on roadways. Flooding, washouts, avalanche hazard, and debris piles on roadways are restricting access in and out of mountain communities.   Road crews have been working around the clock to provide clear travel routes. Blocking snowdrifts, travel routes, and snow piles makes it impossible for crews to complete their work and could interfere with the operations of emergency services.

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