Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
Out of date — this forecast expired 8 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The avalanche danger will remain at MODERATE today due to the possibility of unstable storm slabs still lingering in some areas. Significant uncertainty remains concerning these storm slabs. If any doubts exist about the stability of a slope, avoid it and move on to something lower angle with less uncertainty. New snow expected tonight may allow storm slabs to become more widespread.

Avalanche problems

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Areas where storm slabs may remain possible should have become more isolated. However, continued signs of instability in near and below treeline terrain in some areas (specifically Red Lake Peak) indicate that some unstable storm slabs could still linger in a few places. Given the high degree of uncertainty as to where these storm slabs may linger and whether or not they remain unstable, they still warrant inclusion as a potential avalanche problem. Triggering one of these storm slabs may be easier in areas with numerous trigger points (like convex rollovers, shallowly buried rocks, cliffy areas, etc) or in more complex terrain. They could potentially involve enough snow to bury or injure a person especially in areas around terrain traps. Depending on the amount of new snow that accumulates tonight, storm slabs may become more widespread and reach into above treeline terrain. 

    Recent avalanches, shooting cracks or collapses, or unstable snowpit tests can all help identify where unstable storm slabs may still exist. Actively look for signs of instability and avoid areas with potential problems. In some cases, this problem could lurk in an area where most data seems to indicate stability. If in doubt, assume a slope could remain unstable and avoid it. The high degree uncertainty associated with this problem makes more conservative decision making a good strategy. Low angle slopes are holding great snow and provide less potential for hitting barely covered obstacles.

Avalanche Discussion

* Yesterday, observers on Red Lake Peak (Carson Pass) continued to see unstable test results and some skier-triggered shooting cracks in terrain similar to where the skier triggered avalanche occurred. 

* Snowpit data from Mt. Judah (Donner Summit) did find a patch of buried surface hoar about 20 cm below the surface in one N facing opening at 7900 ft. Snowpit tests targeting this layer did not reveal ongoing signs of instability yesterday.

* Observations from Red Lake Peak, Mt. Judah, Rubicon Peak (West Shore), and Slab Cliffs (Mt. Rose backcountry) all reported widespread surface hoar on all but the southerly aspects at all elevations.

* Decent snow coverage exists in many places, but it is still early season and there are still many obstacles/trigger points on or near the snow surface.  

The limited amount of new snow expected today should not be enough to create new storm slabs, but it could bury the layer of fragile feathery crystals (surface hoar) that currently exists on the snow surface. Buried surface hoar would provide a notoriously weak layer that could allow avalanches to propagate farther across slopes, travel farther down slopes, and break into some less steep terrain. It will not take much new snow to overload that weak layer. If we reach the higher end of forecasted snow totals tonight, more widespread human-triggerable avalanche activity could become possible during the night and by tomorrow morning. If we do not get enough snow to overload that layer, it could linger below the surface and serve as a buried weak layer in a future storm. Tracking where this surface hoar exists and what slopes it may get buried on will help inform where future instability may lurk. If you are out today, please send in your observations to help map this layer. 

Regions covered