Bollettino valanghe

Eastside Region

Eastern Sierra Avalanche Center
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Pericolo valanghe

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

New snow and extreme winds increased avalanche danger overnight. Rapid loading will test the snowpack today and very large avalanches may result. Travel in avalanche terrain is not recommended.

Problemi valanghivi

  • Wind Slabs

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

    Heavy snowfall and strong winds are building reactive slabs in leeward terrain at all elevations today. With extreme wind speeds, you may find slabs lower down slopes and in atypical locations. Even below treeline, watch out for changes in snow surface texture and hardness around terrain features that block or re-direct winds. Shooting cracks and firm hollow-sounding snow are signs that new wind slabs may be unstable in your area. Natural wind slab avalanches are likely and may run full path. Give steep wind-loaded terrain a wide berth, and avoid the runouts of avalanche paths in terrain above you.

    (2/26/2023)

    Large natural wind slab avalanche on a below treeline feature that promotes wind loading.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2.5–3.5

    Recent avalanche activity, collapsing in low-angle terrain, and stability tests continue to raise concerns about faceted weak layers buried under the late February snow.  Persistent slabs can be difficult to assess, predict, and manage. Rapid loading with new snow and wind drifting will likely increase the sensitivity of persistent slabs today.  Persistent slabs may be triggered remotely from flatter terrain below, above, and to the sides of steep slopes, or they might be triggered by a smaller wind slab avalanche.  They can propagate widely and fail in surprising ways that result in larger-than-expected avalanches.  As such, persistent slabs require a wide margin for error. Patience and disciplined terrain choices are the keys to managing risk with persistent slabs. Play it safe by avoiding travel on or below steep terrain where the problem may exist. 

  • Storm Slabs

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

    In areas with over a foot of new snow, storm slabs and loose snow instabilities may be a concern in sheltered areas near and below treeline. Today, storm slabs may be most dangerous on steep slopes with terrain traps, such as trees, gullies, and cliffs, below them. Storm instabilities are most likely triggered at convexities. To avoid these avalanches, steer clear of terrain steeper than 30 degrees until after the storm and then step out cautiously, beginning with smaller test slopes.

    Storm slab triggered at a convexity on a steep slope below treeline.

Avalanche Discussion

An important factor to consider today is the variation in amounts of new snow and water equivalent across the forecast region over the past twenty-four hours. Drainages at the headwaters of the San Joaquin canyon, with Mammoth Lakes as the prime example, received more than twice as much precipitation as elsewhere. Storm slab is dependent on storm snow totals and may be more concerning in areas that have accumulated more snow. 

The threshold for increasing loading on deeper layers in the snowpack may have been reached in the northern part of the forecast area, but rising persistent slab sensitivity may be delayed until this afternoon in areas that have yet to receive an inch of SWE. In the southern part of the forecast area from Rock Creek to Bishop Creek, the snowpack is weaker, and loading from this storm is increasing incrementally. In these areas, storm instabilities may seem comparatively less, but a subtle tip in the balance could suddenly increase the likelihood of a very large natural or human-triggered persistent slab avalanche.

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