Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Cohesive slabs of wind-deposited snow continue to build on a variety of aspects. Use wide safety margins around avalanche paths near and above treeline.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5

    Wind slabs formed by strong shifting winds over the past 48 hours are the main concern today. Plumes of blowing snow over summits and along ridges are signs that wind slab hazard is increasing. Watch for changes in the texture and cohesion of surface snow around terrain features that block or redirect winds. Shooting cracks and hollow-sounding styrofoam snow may mean unstable wind slabs exist under your feet. 

    The hardness of wind-deposited snow means that wind slabs may be triggered from low on the slope or from areas you might consider "safe spots". If triggered, expect these avalanches to propagate across start zones. Recently formed slabs may be thinner and react easily to human triggers, giving a false sense that the problem is "manageable". In other areas, you may encounter older slabs from the last 48 hours that may break suddenly and propagate deeper and wider than anticipated.

     

    Blowing snow reloading start zones ATL on East Peak, Lee Vining, CA.

  • Persistent Slabs

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

    Multiple large and very large natural avalanches were visible on the mountains from Mammoth north to Lee Vining on Monday morning. These avalanches likely released during the night on 12/31 or in the early hours of New Year's Day. While not confirmed, it is probable that these were persistent slab avalanches that failed on the 12/01 facet layer.

    June Mountain Ski Patrol explosive triggered a very large (D3) wet slab avalanche on a NNW aspect at 8500' on 1/1.  This avalanche failed on the 12/01 facets and ran on the ground. Below treeline crown lines were also visible on East Peak above Lee Vining canyon at a similar elevation and may have released on the same layer. The New Year's Eve storm started as rain and observers reported that the lower snowpack became saturated with water below ~9000' and may have caused the onset of avalanche activity at lower elevations.

    The likelihood of human-triggered persistent slab avalanches has decreased since the peak of the storm three days ago. However, a large cornice fall or wind slab avalanche could be enough to initiate a failure at the base of the snowpack causing a very large and destructive avalanche. This situation is most likely to be found in complex terrain near and above treeline where wind loading will continue to develop these potential triggers today. Keep in mind the bigger picture of patterns in natural avalanche activity and current weather red flags such as wind loading. These indicators point towards more conservative terrain choices.

     

    (1/2/2023)

    D3 avalanche triggered with explosives by the June Mountain Ski Patrol on 20230101. The slab failed on wet facets at the base of the snowpack.

Avalanche Discussion

The main uncertainty in the forecast today surrounds actual vs. forecasted winds. With light snow showers overnight last night and ~35 inches of soft snow from the previous storm, there is plenty of slab-building material available in the terrain. If winds maintain at current speeds through the day then natural avalanches will be possible in leeward start zones below ridges. Snow plumes and visible blowing snow obscuring mountainsides are good indications that the forecasted wind slab problem is "on track". Human triggering of wind slabs from the past 48 hours will remain a possibility even if winds drop.

Another factor to consider while tour planning is that an accident, or other problem, that causes you to be out in the mountains after sunset may have higher consequences with another storm approaching tomorrow.  

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