Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Human triggered avalanches remain possible today. Above 8,000 ft, MODERATE avalanche danger exists on NW-N-NE-E-SE aspects on slopes 35 degrees and steeper due to the presence of dense wind slabs and persistent slabs. If any avalanches do occur today, they could break above the person who triggers them and result involve a large amount of heavy dense snow that could easily bury or injure a person. Don't let the new snow lead to careless decision making.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Wind slabs still exist on wind loaded and cross loaded NW-N-NE-E-SE aspects. The largest of these wind slabs will exist above 8500 ft. in near and above treeline terrain where more new snow has accumulated, but smaller wind slabs may still exist on lower elevation wind loaded slopes. While these slabs should have become more difficult to trigger, human triggered avalanches involving these winds slabs remain possible. Most of these wind slabs would break on layers within the storm snow, some of these slabs could fail on or just below the old snow surfaces and behave like the persistent slabs mentioned below. Above 8500 ft. wind loaded slopes 38 degrees and steeper, couliors, unsupported slopes above cliffs, or slopes in complex or extreme terrain represent the best places to find unstable wind slabs today, but they could still linger on any wind loaded slopes steeper than 35 degrees.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    The slabs formed by the new snow resting above an old crust with layers of softer snow around it now represent a persistent slab problem. Even though this kind of avalanche has become more difficult to trigger, this kind of avalanche problem warrants extra caution. So far two human-triggered avalanches have failed at the base of the new snow and propagated along the crust or layers around it. Characteristic of persistent slabs these slides broke above the person who triggered them. Typical obvious clues of instability and other tests may not provide reliable data as to whether or not these persistent slabs will break and when they do break they can break well above the trigger and involve a large amount of dense heavy snow. Often these kind of avalanches don't occur until a person hits the right trigger point on a slope even if several other tracks already exist on the slope. NW-N-NE aspects above 8500 ft. where the new snow rests above an old crust with soft weak snow around it represent the most likely places to find these persistent slabs. Areas where a more shallow snowpack exists or trigger points such as shallowly buried rocks or areas near exposed rocks represent the best places to trigger these slabs from.

Avalanche Discussion

Yesterday a 200 ft. wide avalanche with a 2-3 ft crown occurred on a N-NE facing slope at 9300 ft. on the side of a gully on Relay Peak. This slide only ran downhill for about 100 ft, but it deposited debris 3-5 ft. deep in the gully. It involved all of the new snow that has fallen since Friday and failed on the old crust below the new snow. A snowmobiler riding on the side of the gully appeared to have triggered this slide from below when he or she crossed a more shallow area of the slab above some buried rocks. From this trigger point, it appears that the slide propagated up the hillside. Tests near the crown of this avalanche indicated that the interface between the old crust and the new snow remained weak and that a graupel layer buried about 15 inches from the surface also remained weak. A wind slab avalanche also occurred on the east ridge of Relay Peak on a NE facing slope at about 9500 ft. Other snowpit tests on wind loaded test slopes in the Relay Peak area also showed a weak layer of graupel 1-2 ft deep that fractures could travel along. On the other hand, ski cuts and snowmobile cuts did not yield any results on test slopes in the Relay Peak area.

On Tamarack Peak parties reported no signs of instability. On Andesite Peak up to 8200 ft, observations indicated that the new snow continues to consolidate and bond with itself and the layers below it, and observers reported no signs of instability. Farther south on Red Lake Peak, strong winds continued to transport snow and add snow to the wind slabs throughout the day.

Regions covered