Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

It may be possible to trigger an avalanche at all elevations today. Minimal amounts of new snow this afternoon, strong winds, and our weak snowpack structure are all worth evaluation. Thin coverage will increase the consequences of any avalanche involvement today. When in doubt choosing travel routes with lower slope angles in more sheltered areas will limit your exposure.

Avalanche problems

  • Wind Slabs

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

    Strong winds continue to move around the compass rose. Today’s gale-force winds are expected to shift to the West. It will be possible to find wind slabs ranging in size and distribution on all aspects today. Expect fresh windslab formation this afternoon if snow totals exceed the forecast. Shifting winds following our recent loading event mean that surface clues may be an unreliable indicator of distribution. Do your own localized assessments and be suspect of terrain features that encourage drifting, such as the leeward sides of ridgelines, alpine couloirs, gully features, and cross-loaded depressions. Weak and faceted grains exist throughout the old snow. Keep in mind that even a relatively small avalanche breaking in the upper snowpack has the potential to step down into older snow, creating a larger and more destructive avalanche.

    Shooting crack within fresh windload

    Photo: Steve Mace

  • Persistent Slabs

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

    Weak faceted grains within the old snow continue to show the potential for persistent slab activity. Incremental loading of new snow has not yet been enough to initiate a widespread avalanche cycle. However, recent avalanche activity in the Mammoth area has expanded our distribution to include below-treeline areas. Renewed signs of instability, such as shooting cracks and collapsing in the snowpack following our recent loading event, indicate the continued potential for a large and destructive avalanche. If triggered, a resulting avalanche could break with little warning, involving the full depth of the snowpack. It may be possible to trigger a persistent slab avalanche from adjacent slopes, and avalanches may propagate long distances beyond terrain features that typically contain direct action avalanches such as storm or wind slabs.  Careful route selection and evaluation remain important strategies to manage this problem. When in doubt, choose travel routes with lower slope angles and no overhead hazards to limit your exposure.

    (1/7/2024)

    Remote triggered small Size 1 avalanche on a steep convex slope on NE aspect, 8500’ elevation. Slope scale collapse from skin track with shooting crack travelled to 40 deg rollover. 5 meter wide crown. Failed on 2mm FCs over 1cm crust. 35 cm crown on average. 

    Photo: Ryan Huetter

Avalanche Discussion

The big change today is the expansion of the distribution of our persistent slab problem to include terrain below treeline. Over the past two days, two remotely triggered avalanches were observed in the Mammoth area. Both avalanches were small in size. However, they broke on different weak layers within the old snow. The first failed on a weak layer in the midpack on a feature susceptible to wind loading, while the second broke on basal facets near the ground in a more sheltered area. When dealing with such a shallow and weak snowpack, small changes can often have a significant effect on stability. Recent extreme winds and a couple of days of settlement have added some cohesion to recent snow accumulations, and our run of relatively small storms with long, cold, and dry periods has created several layers of weak faceted snow within the old snow. Remember that recent avalanche activity, shooting cracks, and collapsing in the snowpack are all signs of an unstable snowpack. All of these signs have been observed over the past few days. While today’s minimal snowfall is unlikely to impact our current situation significantly, this could change tomorrow when a more potent storm system impacts the region.

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