Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

Wed
Alpine
4 · High
Treeline
4 · High
Below
4 · High
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Highlights

Very dangerous avalanche conditions exist as a result of continued heavy snow and wind loading.  A buried persistent weak layer has added complexity to a dangerous situation. It will be extremely difficult to maintain adequate safety margins today. Travel in, near, and below avalanche terrain is not recommended.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2–3.5

    Heavy snowfall and strong southwest winds continue to load leeward terrain features at all elevations. Wind-transported snow can accumulate and overload the snowpack much more quickly than storm snow alone. Large and very large natural avalanches are expected to release today in leeward avalanche paths that sit just below ridgelines. With good coverage at lower elevations, very large natural avalanches could run down to valley floors and into lower-angle below treeline terrain.  It's important to be wary of overhead hazards and avoid the runouts of large avalanche paths today.

    (12/28/2022)

    Crown line and bed surface of size 2 human-triggered wind slab in Redcone Bowl

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2.5–3.5

    90" of snow and over 7” of water equivalent have been recorded in the mammoth area over the past 8 days. Heavy snowfall and strong winds today will continue to add stress to persistent weak layers in the upper snowpack. While the sheer weight of our new load may be enough to overwhelm these weak layers in some areas, in others, things may be hanging in the balance. Continued loading by new snow and strong winds will increase the likelihood of large and destructive persistent slab avalanches. While concerning persistent weak layers have been most commonly found on northerly and easterly aspects, a very large remotely triggered avalanche reported on 2/26 occurred on a west aspect. This event is a good reminder of the subtle changes that can occur in the mountains and indicates the importance of conducting your own localized assessments.  Remember that persistent slab avalanches often propagate across and beyond terrain features that would otherwise confine surface instabilities such as wind or storm slabs and persistent slab avalanches can be remotely triggered from adjacent slopes. The best management strategy is to put a wide margin between yourself and the terrain where the problem may exist. When in doubt, avoid being on or underneath slopes greater than 30° in steepness.

  • Storm Slabs

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

    Heavy snowfall rates are expected to continue throughout the day today. Storm instabilities, both slabs, and sluffs may continue to grow in size, becoming more sensitive as the day progresses. Avoid being on or under steep terrain over 30° today and be cognizant of your exposure to terrain features that increase the consequences of avalanches. This includes road cuts, gully features, cliff bands, and mid-slope depressions.

    (12/4/2022)

    20221204 on a NE aspect BTL in the Mammoth Lakes Basin

Avalanche Discussion

As we close out the month of February we are on the cusp of breaking our all-time precip records here in the Eastern Sierra. This week’s storm event continues to be extraordinary. Snow events like this one, especially when paired with an active persistent weak layer, are notorious for producing avalanches that surprise even professionals. Usual "safe routes" should be carefully re-evaluated for exposure to overhead hazards. Better than usual snow coverage at lower elevations means that some avalanche paths may exceed typical max run-outs.  

In addition, there may be unexpected areas with increased avalanche hazards. Lager drifts on exposed roof lines in town or large and steep snowbanks are areas to keep an eye on. Furthermore, very deep and unconsolidated snow will make for difficult travel conditions and has increased the risk of deep snow immersion. Travel in pairs if you venture outside today. Be mindful of unusual and unexpected hazards and keep an eye on pets and small children.

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