Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
View on map

Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
Open full map
Out of date — this forecast expired 9 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

While avalanche activity is unlikely in most areas, the snowpack continues to weaken and human-triggered persistent slab avalanches remain possible in isolated areas where a slab layer exists above loose weak sugary snow (facets). As a result, the avalanche danger remains at MODERATE at all elevations. Identify and avoid areas where a slab layer exists on top of the persistent weak layer of faceted snow. 

Avalanche problems

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    The prolonged dry period combined with a shallow snowpack have caused the existing snowpack to lose strength. A layer of loose weak sugary snow (facets) now exists on northerly aspects across the forecast area. In most areas this persistent weak layer only represents a future concern because no slab layer sits on top of it. However, slab layers do exist on some isolated NW-N-NE aspects in the form of hard wind slabs in near and above treeline terrain and some softer slabs in isolated below treeline terrain. Observations over the last week have indicated that in those isolated areas where the combination of persistent weak layer with a slab on top of it exists, the weak layer has weakened to the point that it can barely support the snow above and the added weight of a person can break that persistent weak layer.  

    Look for cracking as a person weights the snowpack, whumpfing sounds, 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 signs that a slab may exist above weak faceted snow. Clues to instability may be difficult to find unless just the right conditions are present 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.

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.

* 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