Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

Human triggered avalanches are possible today at all elevations. Some of these could involve enough snow to bury a person in areas where the most new snow accumulates. Today's avalanche problems include wind slabs, storm slabs, and loose dry avalanches. MODERATE avalanche danger will exist at all elevations. Evaluate snow and terrain carefully; identify areas where avalanche problems exist; and avoid those areas.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Strong winds and new snow will combine to form wind slabs on wind-loaded N-NE-E aspects and cross-loaded NW and SE aspects. As the winds shift to the NW this afternoon wind slabs may also form on the wind-loaded E-SE-S aspects and cross-loaded NE and SW aspects. These wind slabs will quickly grow in size and depth this morning as snowfall rates increase. These wind slabs will form on top of smooth icy surfaces and weak surface snow. They will form too fast for the wind slabs to bond to the old snow surfaces. The additional weight of a person may be enough to break them loose and cause a wind slab avalanche in some areas. Some of these wind slabs may remain small in areas that do not receive much new snow, but in wind-loaded areas where the most new snow accumulates, avalanches resulting from these wind slabs could involve enough snow to bury a person. 

    Use clues like blowing snow, cornices above slopes, drifted snow, and other wind created textures to identify where wind slabs may exist and avoid traveling on or under steep slopes in those areas in favor of less exposed, less steep, more sheltered slopes where softer snow may reside.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    In many areas, the new snow will accumulate on top of weak old snow (near surface facets). Intense snowfall rates during the peak of the storm mean that the new snow may accumulate too fast for this old weak surface snow to support it. With this weak layer underneath the new snow, the new snow could act as a slab layer even in more sheltered areas resulting in a storm slab avalanche problem. Human-triggered storm slab avalanches will be possible today. Steep NW-N-NE aspects in near and below treeline terrain where the most new snow accumulates represent the most likely places to find fragile storm slabs. 

    Shooting cracks, whumphing, and collapsing can all indicate that human-triggered storm slab avalanches may be possible. Digging into the snow to see if the new snow has fallen on top of old weak snow can also provide a clue that storm slabs may be an issue. Pay attention to your surroundings and look out for clues that storm slabs may exist. If you find those clues move to lower angle terrain where avalanches are unlikely. 

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    In areas where the cold new snow does not form a slab layer, loose dry sluffs could also occur today. Loose dry avalanches should be most prevalent in steep terrain where the new snow accumulates on top of smooth icy old snow surfaces. These sluffs could involve enough snow to knock a person off balance but may not involve enough snow to bury a person. With the current early season conditions, getting knocked off balance could result in getting pushed into a rock, tree, stump or other hard immovable objects. These sluffs would could also have more serious consequences in areas near cliffs or other terrain traps. 

Avalanche Discussion

* Firm, wind scoured snow surfaces and exposed rain crusts exist on most aspects in near and above treeline terrain prior to the storm.

* Variable old snow surfaces ranging from softer weaker snow to breakable crusts to firm scoured surfaces exist in near and below treeline areas.

* Snowpack tests this week have continued to indicate that the old surface snow and the snow just below the surface above the old rain crusts remains weak.

* Decent snow coverage still exists in areas north of Emerald Bay above 8,000'. Below 8,000' snow coverage remains patchy and shallow. South of Emerald Bay, less snow exists with areas below 8,500' holding very little snow.  Snow coverage on southerly aspects has become intermittent and highly variable depending on location.

Regions covered