Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Wind slabs will grow in size and sensitivity today making for dangerous avalanche conditions in leeward terrain. Buried weak layers make it possible for avalanches to break deeper in the snowpack and propagate widely. Look for new wind loading, natural avalanches, shooting cracks, and collapsing as signs of increasing danger. Stick to simple, low-angled, sheltered slopes to avoid the potential for very large avalanches.

Avalanche problems

  • Wind Slabs

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

    Wind slabs will grow in size and sensitivity today as strong southwest winds redistribute new snow that began falling early this morning. Be particularly cautious in areas that get the most snow out of this morning’s storm. Snowfall looks concentrated around the Mammoth area. You may also find higher snow totals in the northern half of the forecast zone, higher elevations, and closer to the crest. You will find dense, deep, rippled drifts on the leeward side of ridgelines and on the sidewalls of gullies near and above treeline. Don’t be surprised to find smaller wind deposits at lower elevations and further down slopes than you may expect. Blowing snow, shooting cracks, and recent natural avalanches are all red flags pointing to unstable wind slabs. Travel in simple, sheltered terrain with limited exposure to wind-loaded slopes above you to avoid dangerous wind slab avalanche conditions. 

    (3/7/2023)

    Intentionally triggered wind slab

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2.5–3.5

    Persistent weak layers have been buried deeply after a series of strong winter storms and triggering them will be more difficult. But, if you find just the wrong spot the resulting avalanche will be very large. In the southern half of the forecast zone, and areas further from the crest, weak facets are closer to the surface and human triggering is a greater concern. The weight of a relatively small wind slab avalanche or a rider moving through terrain may be enough to trigger a large and destructive avalanche. Remember that persistent slab avalanches often propagate across and beyond terrain features and can be triggered from a distance. The best management strategy is to put a wide margin between yourself and the terrain where the problem may exist. Avoid steep convexities, shallow rocky areas, and complex terrain. When in doubt avoid being on or underneath slopes greater than 30° in steepness.

    (3/2/2023)

Avalanche Discussion

Several size 1 wind slab avalanches were reported on northeast aspects near treeline yesterday. One of these was intentionally triggered by a forecaster on a test slope. The other two on Punta Bardini may have been natural or human-triggered. Strong ridgetop winds drifted snow onto leeward terrain throughout the day. New snow and continued strong winds will increase the size, sensitivity, and distribution of wind slabs today. The most hazardous areas will be those that see the highest snow totals this morning. 

Persistent weak layers rest under hard slabs of early March storm snow. From Convict Creek south, these concerning faceted grains are 80 to 110 cm below the surface. They are much deeper between Mammoth and June. Signs of instability from these layers may not be obvious, though triggering an avalanche today has the potential to be devastating. Reevaluate typical “safe zones” and think critically about your exposure to large avalanches. Using conservative terrain choice to put a wide margin between yourself and concerning areas is the best strategy.

Very cold wind chills and decreased visibility could complicate your terrain evaluation, communication, or a potential rescue scenario today.

Keep in mind that the recent run of high-intensity storms has had serious impacts on communities, infrastructure, and road crews. Considerate travel choices and strategic parking will be appreciated if you decide to venture out today. With such good coverage at lower elevations this winter, recent avalanches have been running further, impacting roadways and buildings in the communities of Mono City, June Lake, and Aspendell. Triggering an avalanche above infrastructure could have devastating consequences. Road crews are working overtime to prepare communities for our next round of heavy snow. Blocking snow drifts, travel routes, and snow piles makes it impossible for road crews to finish the job. Be aware that CalTrans and Inyo County will put road restrictions in place in the Bishop Creek drainage today.  With an intense atmospheric river storm rolling into our area Thursday afternoon, we can expect potential flooding impacts, limited plowing, and restricted parking in other areas as well.

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