Avalanche forecast

Eastside Region

Eastern Sierra Avalanche Center
View on map

Avalanche danger

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Out of date — this forecast expired 3 years ago.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

Highlights

New snow and strong winds will increase avalanche hazard throughout the day today. Weak snow at the base of the snowpack continues to show the potential for large and deadly avalanches. When in doubt choosing travel routes with lower slope angles in more sheltered areas will limit your exposure.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–3

    Weak faceted grains within the old snow continue to show the potential for persistent slab activity. If triggered, a resulting avalanche could break with little warning, involving the full depth of the snowpack. It will be possible to trigger a persistent slab avalanche from adjacent slopes today. Avalanches may propagate long distances and beyond terrain features that typically contain surface instabilities such as storm or wind slabs. Recent observations have shown that the sensitivity of this problem ranges from stubborn in areas with deeper snow coverage to reactive in areas with more shallow coverage. Managing this problem is made more difficult because shallow and inconsistent snow coverage means that the few areas attractive for riding are generally the same slopes where the avalanche problem exists. Persistent slab problems require persistent patience and extensive evaluation. Cautious route selection remains the most important strategy to manage this problem. Choosing travel routes with lower slope angles and no overhead hazard will limit your exposure.

    Large remotely triggered avalanche. North side of Dunderberg - N/NE Aspect 10400'

    Photo: High Sierra Snowcat

  • Wind Slabs

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

    Winds have already shifted to the southwest and increased in speed. Add some new snow to the mix and you should expect fresh wind slab development near and above treeline today. Blowing snow, recent drifting, and hollow drum-like snow surfaces are all signs that can clue you into nearby wind deposits. Be suspect of terrain features that encourage drifting, such as the leeward sides of ridgelines, alpine couloirs, gully features, and cross-loaded depressions. It is critical to remember that the distribution of wind slabs overlaps with our persistent slab problem. This means that even a relatively small avalanche breaking in the upper snowpack has the potential to step down into older snow, creating a much larger and more destructive avalanche.

    (1/5/2024)

    Northeast aspect, 10,000 ft. Sherwin Ridge

    Photo: Clancy Nelson

Avalanche Discussion

Recent Avalanche activity.

Significant natural activity that likely occurred during our recent loading event on 1/22 was observed yesterday, including widespread soft slabs and loose dry sluffs up to D2 and several persistent slab avalanches up to D3 in size. Mitigation efforts on Mammoth Mountain resulted in several large soft slab avalanches and a couple of avalanches breaking down near the ground on basal facets. A remotely triggered avalanche near treeline in the Virginia Lakes area initially broke as a wind slab but quickly stepped down to depth hoar on the ground, resulting in a D2.5 avalanche with a 6’ crown.

Thoughts on our persistent slab problem.

Describing the distribution of this problem has been tough. When looking at our forecast area from the 30,000’ foot view, coverage is generally specific or even isolated in the southern part of the range. However, where we do have adequate coverage, the problem feels more widespread, making it hard to avoid. Further complicating the situation has been the incremental loading of our snowpack. Our winter season has been marked by small storms that have had little impact on the coverage but have been having an “outsized” impact on stability. Recent observations have indicated that our persistent weak layers have been becoming more stubborn in areas with deeper snowpacks. We suspect this is not because the basal facets have "healed" but rather that they have become harder to trigger. The slab has taken longer to form in areas with more shallow coverage (outside of the mammoth area), and connected slopes are more isolated in nature. Following our most recent storm, these persistent weak layers are more reactive to human trigger, and this problem is starting to show its teeth.

The Big Picture.

This season is far from “typical,” and the problems we are dealing with are not what we are used to. When trying to navigate the unknown or atypical, it’s important to remember the basics. Avalanches are weird and unpredictable. New snow and wind will lead to increasing hazard.  And most importantly, terrain choice is the only thing we can control. Choosing travel routes on lower slope angles without overhead hazards is never a bad idea.

Regions covered