Bollettino valanghe

Eastside Region

Eastern Sierra Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Slabs of drifted snow may be sensitive to human triggers in leeward terrain. Buried weak layers have been challenging to assess. They have caused some avalanches to break widely and caught people off guard mid-slope. You can hedge your bets against unwanted surprises by giving yourself a wider margin for error and having options that include simple, sheltered terrain with low slope angles.

Problemi valanghivi

  • Wind Slabs

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

    In areas with moderate to strong winds and enough snow available for transport, fresh sensitive drifts could develop in leeward terrain. In isolated areas, you could still trigger older, harder, and larger drifts. Specific features of concern include steep slopes below ridgelines, the sidewalls of gullies, and cross-loaded depressions. Recent avalanche activity, cracking within the surface snow, recent cornice growth, and hollow upside-down feeling snow, are all clues that wind slabs may be unstable in your area. If triggered, avalanches could propagate widely, breaking above or around your skis, board, or machine. Sheltered terrain with lower slope angles may hold softer snow and safer riding.

    (3/19/2023)

    Triggered wind slab in June

  • Persistent Slabs

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

    In isolated areas, a reactive crust/facet combination is buried up to two feet deep under snow from the past week's storms. Yesterday, forecasters got shooting cracks and collapses on this layer in the Bishop area. It has also been the prime suspect in several natural and human-triggered avalanches from south of the forecast zone, the Sherwins, and the June backcountry over the past several days. Use caution in areas that had firm snow surfaces before the March 19th storm. Track weaker snow throughout your day by digging and probing. The most common signs of instability are shooting cracks, collapsing, and remotely-triggered avalanches. That feedback may not be consistent and avalanches have caught people by surprise. Be careful around wind-loaded terrain and convexities. You can build a wider safety margin into your tour plan to limit your exposure to a problem that is difficult to assess.

Avalanche Discussion

We saw a period of avalanche activity through 3/24. Many natural and human-triggered slabs to size 2 released on north, east, and southeast aspects. In some of these avalanches, observers identified persistent grains at the failure plane. Forecasters in Bishop Creek yesterday (3/25) continued to see signs of instability, like shooting cracks and collapses, on those small facets at all elevations up to about 10,000 feet.

The layer of concern consists of fragmented grains mixed with near-surface facets that formed atop crusts and firm wind-packed layers between 3/16-3/18. This layer was subsequently buried by two significant storms, one on 3/19 and one on 3/21, which added up to 1-2 feet of snow over that interface.

Another weak faceted layer buried on Valentine’s day sits around 2 meters deep and avalanches on this layer are now unlikely. In isolated pieces of terrain, a large natural trigger could still produce an avalanche breaking within old snow layers. For example, a very large deep slab avalanche released on the east aspect of Mt. Wood on March 21st. 

Considerate travel choices and strategic parking will be appreciated as road crews continue to manage the extraordinary snow load this season. With good coverage at lower elevations this winter, recent avalanches have been running further, impacting roadways and buildings in the communities of Mammoth, Virginia lakes, Mono City, June Lake, and Aspendell. It is important to practice good run-out awareness. Triggering an avalanche above infrastructure could have devastating consequences.  Remember that it often takes multiple passes to clear roadways and trailhead parking. Road crews are working overtime to allow access to communities that have been stranded by heavy snow, avalanche activity, and flood damage. Blocking snow drifts, travel routes, and snow piles makes it impossible for road crews to continue their work.

Regioni coperte