Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 4 years ago.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

Highlights

Small, isolated pockets of wind slab are still reactive to human triggering. Look out for signs of instability above treeline where slabs are sitting on weak snow.

Avalanche problems

  • Wind Slabs

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

    Alternating wind events following the last storm created wind slabs on most aspects near and above treeline.  Slabs that formed from major wind events in the wake of our last storm (SW wind on 2/5/23 and NE wind on 2/6/23) have largely become unreactive. These slabs would likely need a large trigger like a cornice fall to release. However, there are isolated areas where the wind-deposited snow overlies soft weak snow, especially in protected terrain above treeline.  Be suspect of features that encourage drifting such as the leeward sides of corniced ridgelines, gully features, and cross-loaded depressions, especially those with textured, pillowed surface snow and a cornice looming over them. You can track the extent of this problem by periodically assessing surface snow as you move through terrain. Check for the presence and depth of cohesive layers. Look for shooting cracks around terrain features that block or re-direct winds, especially when transitioning to steeper terrain.

    (2/8/2023)

    Skier Triggereed D1.5 in Elderberry Canyon. 11,400' ENE aspect. Failed on facets under recent wind deposited snow.

Avalanche Discussion

Yesterday a small (D 1.5) skier-triggered avalanche was reported on an ENE aspect at 11,400' on Mt. Tom.

While you can find strong wind-deposited snow in many areas near and above treeline, most of these slabs are unreactive to human triggering. However, recent observations indicate that it is possible to trigger small pockets of wind slab in isolated areas, especially in the alpine. There is moderate uncertainty around size potential with these pockets. While the largest recent avalanche was small, data from the alpine are lacking, so the size range in today's forecast is up to 2 (large) at the highest elevations.

January closed with a period of mostly dry weather and a single light snowfall. The mix of sun, wind, and low-density surface snow led to the development of a variety of persistent grains (facets) and crusts in the upper snowpack. The most recent snowfall on 2/4/23 subsequently buried these layers in isolated areas. While we have seen propagating test results in recent days on non-persistent layers, it is likely that the wind slab problem is still reactive where the slab overlies the weak old snow.

Adding to the mixed bag of weather and snowpack factors is the potential for warming today.  Temperatures will reach above freezing up to ridgelines in the Mammoth area and will affect the snowpack. There has been gradual warming over the past few days with good refreezes each night. As such, the snowpack has started to adjust to sun and warmer temperatures. Wet loose avalanches are unlikely, but it is worth tracking the amount of melting in the surface snow on solar aspects. Rollerballs and pinwheels are early indications that wet snow instability may develop later in the day.

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