Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Lots of avalanches were triggered yesterday by backcountry travelers.  New snow and wind will further fuel the instability today. Conditions are tricky right now. Consider avoiding avalanche terrain altogether or at least avoiding NW-N-NE aspects at the present time.

Avalanche problems

  • Wind Slabs

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

    There are instability concerns ongoing for unstable wind slabs that were triggered as avalanches yesterday as well as for new wind slabs that are formed today. The wind slab avalanches that occurred yesterday were formed under SW wind conditions. New wind slabs that form today will do so under E to SE wind conditions. This leads to the potential of encountering an unstable wind slab on any aspect today in near treeline or above treeline terrain. Some of the wind slabs on NW-N-NE aspect terrain may sit on top of buried surface hoar allowing for wider than usual propagation as a persistent slab avalanche.

    Due to the complexity of the current avalanche situation, simply identifying where the most recent wind drifting snow is depositing will not identify all of the slopes of concern. All avalanche terrain in near treeline and above treeline terrain are currently suspect or will become suspect as today's storm progresses. If you are determined to travel in avalanche terrain today, choosing E-SE-S-SW-W aspect terrain in wind protected areas below treeline has the lowest chance of triggering an avalanche today.

    (3/20/2023)

    An unintentional skier triggered wind slab avalanche with wide propagation on a NE aspect, Stevens Peak, Carson Pass area, CA.

    Photo: Public

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    A layer of surface hoar exists on top of the prominent March 14 rain crust in some locations on NW-N-NE aspect terrain. Two of the avalanches that occurred Monday were confirmed to have failed on this weak layer. Additional snowfall today will increase the slab depth and increase the stress on this weak layer. It is not clear exactly how widespread this avalanche problem is, which makes it more likely to catch someone by surprise. Any persistent slab avalanches will have wider than usual propagation.

    Uncertainty around a persistent weak layer means that now is not a good time for aggressive terrain selection. Opting for non-avalanche terrain if traveling NW-N-NE aspects is highly recommended. Due to the potential spotty distribution of buried surface hoar, it will be difficult to determine exactly which slopes or specific sections of larger slopes do or do not hold this weak layer. Consider avoiding NW-N-NE aspect avalanche terrain, especially if you see any signs of wide propagating avalanches, unstable snowpit test results, snow surface cracking, collapse, or whumpfing.

    (3/20/2023)

    An unintentional snowboarder triggered avalanche on the N side of Castle Peak. Buried surface hoar confirmed as the failure layer. Donner Summit area, CA

Avalanche Discussion

  • Numerous avalanches in the size D1 to D2 range were triggered yesterday by backcountry travelers on N to NE aspects in the Donner Summit, West Shore Tahoe, and Carson Pass areas. Most were wind slabs. At least two involved buried surface hoar.
  • An incomplete report was received of a solo skier who managed the unlikely survival of full burial in an avalanche yesterday on Round Top Peak in the Carson Pass area.
  • Unstable snowpit test results were noted yesterday in wind loaded areas both with and without buried surface hoar.

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