Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Instability within recent wind-deposited snow is the primary concern today. Large human-triggered avalanches were reported in simple terrain yesterday. Avoid steep wind-loaded avalanche paths. Use caution even around smaller terrain features.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–3

    Wind loading preceded and continued throughout yesterday's storm. Reactive wind slabs of varied depths formed on leeward terrain features, creating unpredictable and dangerous conditions. These avalanches are most likely near and above treeline, but yesterday's large human-triggered avalanche on an exposed terrain feature at 8800' is a good reminder that even low-elevation terrain can be better described as near treeline if it has attributes that promote wind-drifting. If trying to gain information on the wind slab problem in your area choose test slopes carefully. Make sure the slope is not large enough that a deeper wind slab breaking behind you would cause harm.  Avoid wind-loaded leeward avalanche terrain today, especially below ridgelines and around terrain features that block or re-direct winds.

    Human-triggered wind slab avalanche on a  low-elevation terrain feature that is better-described as near treeline. 1/14/23

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    The most recent storm began with soft low-density snow and progressed to periods of higher intensity with rates up to 3" per hour yesterday afternoon. As a result, the top 12 to 24" of the new snow is "upside down". Yesterday, the upper cohesive layer formed a slab that failed easily within the new snow. Field observations in the past 24 hours report touchy, but mostly small storm slabs. In isolated areas, with deeper new snow these avalanches could be large enough to bury a person. Terrain traps like gullies and tree wells that concentrate debris could increase the consequences of a small avalanche.  Expect this problem to become less sensitive over the course of the day.

    Debris from a small natural storm slab in dense forest. 1/14/23

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    3–4

    Heavy snowfall and wind loading will test the strength of persistent weak layers at the base of the snowpack. The November layer of faceted snow is now down 1.5 to 2m below the snow surface. At this depth, the deep persistent slab is unlikely to be triggered by a person. However, on 1/9/23 during heavy wind and snow loading a natural avalanche stepped down and released at the base of the snowpack on a NW aspect above Aspendell, Bishop Creek. If triggered, deep slabs can propagate around terrain features that would otherwise confine new snow instabilities creating larger-than-expected avalanches. The possibility of these larger avalanches is another good reason to avoid wind-loaded start zones of defined avalanche paths.

    Profile of the most recent confirmed Deep Persistent Slab avalanche.

Avalanche Discussion

Uncertainty exists surrounding the old snow surface that was buried on 1/13/23 by wind-loading preceding yesterday's storm. This layer is buried over a meter deep in areas that are favored by wind loading. Field visits by forecasters turned up evidence of instability on this layer including a large avalanche referenced in the wind slab problem text. Expect the depth of this interface to mean that it is stubborn to trigger. Typical tests for new snow instability like slope cuts and hand shears may only highlight shallower layers within the storm snow. Be careful not to gain too much confidence in your new-snow hazard assessment from data on shallower layers. It will be difficult to gather enough information to effectively "manage" the deeper wind slab problem during your tour today. The best strategy would be to not "step out" today in wind-loaded terrain.  

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