Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Today's snow and wind will deposit new slabs of wind-blown snow on exposed slopes near ridges and gullies. Layers of storm snow could also still break loose on steep slopes in more sheltered areas. Cautious route finding and conservative decision-making are essential while traveling in the backcountry to avoid these avalanche concerns.

The avalanche danger will increase tomorrow, as a stronger winter storm impacts the area. 

Avalanche problems

  • Wind Slabs

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

    New snow and SW winds will build new wind slabs on open slopes in near and above treeline terrain today. These will start small but will grow in size and extent as new snow accumulates. They accumulate faster than they can bond to the snow below them. People would likely trigger wind slab avalanches on steep slopes where wind-blown snow piles up today, and natural avalanches may be possible in areas with the most intense wind loading. The most fragile wind slabs will form on NW-N-NE-E-SE aspects near ridges, on open wind-exposed slopes, and in gullies. Stiffer, more difficult-to-trigger wind slabs may linger on slopes loaded by yesterday's NE winds. 

    Recent avalanches, blowing snow, cornices above a slope, wind pillows, and wind-created snow surface textures indicate the presence of wind slabs. Since they can exist on almost any aspect and there are several layers of overlapping wind deposits, assume that most open areas could have wind slabs on them. Focusing on terrain sheltered from the winds can help avoid the wind slabs and this sheltered terrain should also hold better snow quality.

    (2/25/2023)

    Human-triggered wind slab avalanche on Trimmer.

    Photo: Public

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2.5

    Many people reported finding more dense snow on top of lighter snow yesterday. Storm slab avalanches were also reported yesterday. This upside-down layering in the storm snow and other storm snow weaknesses could still break under person's weight and produce storm slab avalanches today. Today's additional snow will add more storm snow on top of the 3 to 4.5 feet of new snow that fell this week. The prevalence of storm slabs could vary greatly across the forecast area due to variable snow totals, winds, and temperatures. 

    Get out of existing tracks to look for cracking in the storm snow and feel for light snow below heavier layers of snow as you travel through terrain today.  If you see any signs of storm snow weakness or have any doubts about a slope's stability, move to lower angle non-avalanche terrain.

    (2/25/2023)

    Storm slab avalanche on lower Trestle Peak.

    Photo: SAC

Avalanche Discussion

Recent Observations:

  • Human-triggered storm slab and wind slab avalanches were reported yesterday. 
  • Many people reported heavy snow on top of lighter snow across the forecast area yesterday. Other potential storm snow weaknesses like graupel, density changes, and potentially some weakness at the new snow/old snow interface below a surface crust have all been found within the recent storm snow.
  • A thin crust formed on some SE-S-SW slopes during yesterday's warm-up. 
  • Some layers of old graupel, facets, and/or buried surface hoar can be found about one to two feet below the recent storm snow on some NW-N-NE aspects. No avalanche activity or signs of instability has been reported on these old layers during this storm cycle. 

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