Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
View on map

Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
Open full map
Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Wind drifted snow and new snowfall loaded onto a weak existing snowpack have created dangerous avalanche conditions. The hazard is complicated by the potential to trigger avalanches low on the slope, well below traditional avalanche start zones. There is a high likelihood of serious trauma for anyone caught in an avalanche in the currently rocky, shallow snowpack. If in doubt or faced with uncertainty, choose not to travel in or below avalanche terrain.

Avalanche problems

  • Wind Slabs

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

    Gale force SW winds have drifted and deposited new snow into cohesive wind slabs. This avalanche problem exists mainly above treeline and near treeline across NW-N-NE-E-SE aspects. Unstable wind slabs may also have formed below treeline in some areas due to the strength of the recent winds.

    Look for clues indicating the presence of wind slabs such as visible drifting snow, cornice formations, wind drifts, wind textured snow surfaces, and scouring vs deposition patterns on the ground. Consider avoiding areas where wind drifting snow has deposited, especially if weak faceted (sugary) snow exists in the snowpack below.

    An example of wind slab clues such as cornice, wind drifts, and snow surface cracking. 12/03/2023 near Castle Peak, CA

    Photo: SAC

  • Persistent Slabs

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

    New snow has loaded on top of a weak, faceted snowpack in some portions of the forecast area on NW-N-NE aspects. The structure of the snowpack varies widely by location and by elevation. Regardless, numerous problematic weak layers exist. None of them are expected to handle new snow loading very well or to stabilize quickly post storm.

    While wind slab is the most widespread avalanche problem today, persistent slab is the more difficult problem to manage. Signs of instability such as recent avalanches, snow surface cracking, snowpack collapse, or whumpfing sounds are indications to avoid NW-N-NE aspect avalanche terrain in the area. Keep in mind that previous NE wind events may have scoured weak snow out of the upper portion of a slope, laying a trap of weak snow on the lower half of the slope that is just waiting for a trigger. Anticipate wider avalanches that are triggered lower on the slope than what commonly occurs for wind slabs.

Avalanche Discussion

 

More on the persistent slab problem: In most areas, the weak faceted (sugary) snowpack exists above about 8,000', but could be encountered as low as 7,200' in isolated locations. Look for an easy to miss thin layer of faceted snow on top of the uppermost rain crust in the snowpack (photo below). As elevation increases expect to find layers of faceted snow in between rain crusts. Above about 8,500' or so, rain crusts disappear and the snowpack becomes nearly all weak faceted snow. Generally speaking, the higher up you go on wind protected NW-N-NE aspects, the weaker the snowpack.

There is still the potential to hit many obstacles (rocks, logs, open water, bushes, etc.) that are barely covered (or not) by the shallow snowpack. Areas with a supportable rain crust in the 7500’ to 8500’ elevation range provide the most usable snowpack. Anticipate encountering a different snowpack structure and a different set of travel conditions if you are moving from one place to another around the forecast area.

Regions covered