Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Additional wide propagating avalanches occurring in below treeline areas remain a concern today. Ongoing blowing and drifting snow will keep areas of unstable snow near ridgetops and gully features ongoing. Consider avoiding avalanche terrain and opting for lower angle slopes in areas where signs of instability such as drifting snow, snow surface cracking, or recent avalanches are present.

Avalanche problems

  • Wind Slabs

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

    Several wind slab avalanches were reported yesterday, some natural, most triggered by backcountry travelers. Ridgetop winds shifted from SW to out of the NE around 8 pm last night. NE winds have been strong enough to cause blowing and drifting snow since about 1:30 am. These winds will have redistributed snow on the ground and created areas of new wind slabs in near and above treeline terrain. In cross-loaded areas, today's wind slabs will have deposited on top of yesterday's wind slabs. Today's winds slabs will be most widespread on SE-S-SW-W-NW-N aspects, but could also linger as leftovers from yesterday on other aspects and below treeline.

    Use clues such as drifting snow, smoother snow surfaces in wind exposed areas near ridgetops and gullies, snow surface cracking, and recent avalanches to identify areas where unstable wind slabs might exist. Consider avoiding avalanche terrain and opting for lower angle, conservative terrain choices any time snowpack stability is in question.

    (2/5/2023)

    One of two wind slab avalanches triggered from adjacent low and angle terrain on the E aspect of Mt. Lincoln around 7,800', Donner Summit, CA.

    Photo: Public

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–2.5

    Concern continues today for wide propagating avalanches that are triggered by backcountry travelers in below treeline areas. There is a buried layer of surface hoar a few inches below the recent storm snow and a new layer of graupel from the start of the recent storm snow. Failure of either of these weak layers could produce similar type avalanches today. Wind protected, open slopes in below treeline terrain across NW-N-NE aspects are the most suspect, but this type of avalanche could occur on other aspects today.

    Any avalanches that occur on this weak layer are expected to have wide propagation. Persistent slab avalanches could be triggered from very low on the slope or from connected terrain to the side. Adjust your terrain selection and route finding today to match the avalanche potential. The combination of a persistent slab avalanche problem and steeper terrain above has contributed to many avalanche accidents in the past. This is different than the typical post storm stabilization, please adjust accordingly.

    Looks for signs of persistent instability below treeline such as snow surface cracking and recent avalanches. Use low angle, non-avalanche terrain without connected steeper above or to the side if signs of instability are present or snowpack stability is in question.

    (2/5/2023)

    One foot crown of an approx 200' wide avalanche that was unintentionally triggered in below treeline, NE aspect terrain on Hidden Peak, West Shore Tahoe, CA.

    Photo: Public

Avalanche Discussion

  • At least 7 avalanches were reported yesterday. Some were natural, most were triggered by backcountry travelers. Poor visibility yesterday has kept the extent of the natural avalanche cycle largely unknown.
  • Signs of unstable wind slabs, persistent slabs, and storm slabs were observed yesterday in a variety of locations.
  • The layer of surface hoar that was buried on Jan 29 varies widely by location in both crystal size and weakness.

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