Bollettino valanghe

Eastside Region

Eastern Sierra Avalanche Center
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Pericolo valanghe

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

In sintesi

Heavy snowfall, extreme winds, and low-elevation rain are overloading an uncertain snowpack. Very large avalanches are expected and in some cases may reach historic runouts. Travel in and below avalanche terrain is not recommended.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Certain
    Dimensione
    1.5–3.5

    Over the past twenty-four hours, strong to extreme SW winds have formed 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 on 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 winds, avalanches like this one may release naturally.

    Photo: Matt Irons

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Certain
    Dimensione
    1–2.5

    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 13" of new snow in the past 24 hours, and snowfall rates over 2" 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.

    A large storm slab avalanche on a convex roll below treeline.

  • Persistent Slabs

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

    A persistent weak layer of faceted snow buried in late February is now 3-4ft below the snow surface. Rapid loading from new snow, rain, and wind transport may cause very large persistent slab avalanches to release naturally. Persistent slab avalanches can propagate widely, connecting multiple start zones and terrain features resulting in larger-than-expected avalanches. 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 safe zones.

Avalanche Discussion

Snowfall overnight did not reach forecasted values. Uncertainty today is focused on precipitation amount and type. Storm slab and wind slab avalanche size depend on the amount of snow available for slab formation. Today's total snowfall will determine whether avalanche activity meets expectations. Snow levels are forecasted to remain below 8500' on Friday, so rain on snow should be limited to lower elevation start zones for a short duration. If snow levels are significantly higher, widespread wet slab and wet loose activity below treeline may result. Even with freezing levels remaining relatively low, there is a chance to see some wet snow instability. Rising temperatures and rain on snow may increase the likelihood of roof avalanches in mountain communities.

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