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

MODERATE avalanche danger exists at all elevations today due to isolated persistent slabs in areas where a slab layer exists above loose weak snow and rain on snow creating loose wet instabilities. Human-triggered avalanches will be possible today. While most avalanches should remain small, the shallow snowpack and numerous exposed obstacles can provide large consequences for any size avalanche. Evaluate snow and terrain carefully. Identify where instabilities may exist and avoid those areas in favor of less steep slopes.

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    A widespread layer of loose weak sugary snow (facets) exists on many northerly aspects across the forecast area. In most areas, little no slab layer exists above this persistent weak layer, but some isolated slab layers do exist above this weak layer on some NW-N-NE aspects. In near and above treeline terrain, a few hard wind slabs still linger above this layer. In below treeline terrain, some isolated softer slabs exist above the weak layer. Observations and data collected from those isolated areas where this combination of slab over weak layer exists indicate that the weak layer can barely support the snow above it. The additional weight of rain and snow from this storm may make these isolated persistent slabs easier to trigger today. Human triggered persistent slab avalanches remain possible today. Most of these persistent slabs should remain small, but they could still involve enough snow to cause problems for backcountry travelers.

    Human-triggered cracking, collapsing or whumpfing, a hollow sounding snowpack, feeling a softer weaker layer of snow below the surface with a probe or pole or hand pit, unstable snowpit tests, and any other signs that a slab may exist above weak faceted snow may indicate that a persistent slab problem exists. Clues to instability may be difficult to find unless just the right combination of slab over weak layer exists, and an isolated human-triggered avalanche may represent the first clue to an unstable slope. Use safe travel protocols when traveling in and around avalanche terrain.  A shallow snowpack with numerous barely covered and still exposed obstacles would magnify the consequences of any size avalanche.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Loose wet avalanches will be possible today. The northerly aspects below 8500 ft. where loose weak snow exists on the surface represent the most likely places for loose wet snow instabilities, but loose wet snow could form on any slopes where wet snow exists or on slopes that receive rain today. Today's wet snow instabilities could include pinwheels, roller balls, or point release avalanches. They may entrain enough snow to knock a person down or push them off course. Terrain traps and exposed obstacles could magnify the consequences of these loose wet avalanches.

Avalanche Discussion

* Observations in the Carson Pass, Desolation Wilderness, West Shore Tahoe,  Deep Creek, Pole Creek, and Donner Summit areas during the last week continue to reveal signs of persistent slab instability including snow surface cracking, whumpfing, and/or unstable snowpit test results. This instability exists on NW-N-NE aspects in some isolated areas where loose sugary snow (facets) exists below either a hard or soft slab.

* Loose weak sugary snow (near surface facets) without an overlying slab is fairly widespread across the forecast area on northerly aspects in wind protected, below treeline areas.

* Snow surface conditions range from wind scoured snow and firm ice in near and above treeline terrain to lingering areas of soft unconsolidated snow on sheltered northerly aspects below treeline.

* Some areas of wet surface snow existed up to at least 8300 ft. yesterday near Grouse Rocks. 

* Northerly aspects above 8000 ft in the Mt. Rose area and along the Sierra Crest north of Emerald Bay hold the best snow coverage at 2 to 3+ feet. Overall less snow cover exists south of Emerald Bay, but decent coverage exists above 8,500 ft. on northerly aspects in the Carson Pass area.  Coverage becomes patchy on other aspects with large areas of bare ground on many southerly aspects at all elevations.

Regions covered