Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

MODERATE avalanche danger exists both near treeline and above treeline on NW-N-NE-E-SE aspects on slopes 35 degrees and steeper due to ongoing wind slab development. For all other areas, LOW avalanche danger exists. Persistent slab avalanches are unlikely but not impossible in open areas below treeline and near treeline on NW-N-NE aspects.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    With SW ridgetop winds in the light to moderate speed range for much of the day yesterday, significant amounts of snow on the ground remain available for wind transport. As ridgetop winds increase today, expect to see areas of blowing snow and new wind slab development in directly wind loaded and cross loaded areas near treeline and above treeline on NW-N-NE-E-SE aspects. Uses clues such as blowing snow, cornice formations, wind pillows, and cracking along ridgeline edges to determine where wind slabs exist. Unlike other avalanche problems, wind slabs are constrained by terrain and often have well defined visual boundaries, making them easier to avoid.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    Persistent slab avalanches remain a lingering concern where a weak layer of collapsed surface hoar capped by thin crust exists around 12 to 24 inches deep in the snowpack. This weak layer is most often found along the Sierra Crest in open areas below treeline and near treeline on NW-N-NE aspects. Human triggered avalanches are unlikely to occur on this weak layer today. That said, in the locations where this weak layer is found, day after day snowpit tests continue to indicate that the right set of slab over weak layer ingredients are in place for avalanche activity to occur. Avoid complacency and pay attention to slope angle at all times, on the fly, both uphill and downhill. Question the placement of uphill tracks by others and set a new track if the placement is poor, exposes more than one person at a time to avalanche terrain, or has high consequences if a avalanche were to occur. Previous tracks on a slope are not a sign of intelligent life. They often just give a false sense that a poor decision was somehow okay.

Avalanche Discussion

Observations made yesterday on Silver Peak (Pole Creek area) revealed small wind slabs 4 to 8 inches thick in areas of direct wind loading both near treeline and above treeline. Skier triggered cracks up to 6 feet long was observed when weighting the edge of ridgline wind pillows. The persistent weak layer of collapsed surface hoar capped by thin crust was absent in this area. Reports were received from Andesite Ridge (Donner Summit area), Rubicon Peak (West Shore Tahoe area), and from above treeline terrain on the west side of Carson Pass. On Andesite Ridge little wind affect was observed with generally good bonding reported at the old/new snow interface. On Rubicon Peak continued unstable snowpit results were reported occurring on the persistent weak layer of collapsed surface hoar and thin crust on a N aspect in near to below treeline terrain. West of Carson Pass unstable wind slabs up to 3 feet thick were reported above treeline with snowpack failure occurring within the recent storm snow.

Regions covered