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

Avalanche danger is rising rapidly as another atmospheric river impacts the Eastern Sierra. Deep accumulations and wet heavy snow at lower elevations combined with wind loading will test buried weak layers. Travel in avalanche terrain is not recommended. Avoid the runouts of large avalanche paths.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Certain
    Size
    2–3.5

    Increasing heavy snowfall and extreme winds will build cohesive layers of wind-deposited snow in leeward terrain features today. Wind-deposited snow accumulates more quickly than direct snowfall alone meaning that wind slabs in start zones below ridgelines, or in cross-loaded terrain features may be many times larger than the amount of snowfall measured at weather stations. Wind slabs may run farther than expected due to better-than-usual coverage in tracks, especially at lower elevations. Stay well away from the runouts of large avalanche paths with leeward start zones.

    A large natural Wind Slab avalanche in the June Lake area. 2/14/13.

  • Storm Slabs

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

    Storm slabs form during periods of intense precipitation when a cohesive layer of dense snow does not bond well to the layer below. Storm slabs can release at the interface between the new and old snow, or on a layer within the storm snow.  Be aware of small steep slopes like road cuts, snowbanks, and roofs especially when they end in confined areas where snow can pile up. Avoid travel on or below slopes greater than 30 degrees. Today and tonight, snow levels are expected to rise to between 7,500' and 8,000'. On low-elevation slopes and in mountain communities below 8,000,' less accumulation and heavier wet snow may lead to wet slab and wet loose activity.

    (3/10/2023)

    Slab avalanche 18 inches deep on a snow bank in Mammoth Lakes. 3/10/23.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2.5–4

    A persistent weak layer of faceted snow buried in late February is now approximately 5-9 ft. below the snow surface. Rapid loading from new snow, rain, and wind transport will test these layers yet again and may be enough to trigger deep persistent slab avalanches today. In addition to rapid loading, potential deep slab triggers may include other avalanches such as wind slabs or cornice falls. Deep Slabs can propagate widely, connecting multiple start zones and terrain features resulting in larger-than-expected avalanches. With good coverage in the tracks of avalanche paths at all elevations, these avalanches could reach maximum runouts and impact areas like mature forests and flat terrain usually considered safe zones. Far-running avalanches are likely to entrain the wet low elevation snow, increasing their destructive potential.

    (3/13/2023)

    Crown of a Deep Persistent Slab avalanche. NE, 10000' on McGee. 3/13/23

Avalanche Discussion

Snow levels are once again a source of uncertainty. For snow-covered terrain below about 7500' there will likely be a mix of avalanche problems including wet loose  Today's atmospheric river will favor the northern part of the forecast area, but significant snowfall and wind loading are expected region-wide in the next 24 hours.

Depending on the timing of snowfall we should reach HIGH avalanche danger at all elevations by mid-day today. Conditions will continue to deteriorate overnight as significant weight is added over the deep slab problem.

Explosive triggered deep slab avalanches in the past 48 hours indicate that the deep persistent slab problem is still sensitive to larger triggers. The expected size for deep slabs is increasing and there is potential to reach historic runouts in some paths overnight tonight.

 

Regions covered