Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

New snow is expected to drift and deposit into fresh, cohesive slabs today along the downwind side of ridgetop areas. Lingering, isolated instability in the lower half of the snowpack is still a concern, especially along the eastern side of the forecast area. Identify and move cautiously around areas of drifting snow. Maintain wide safety margins to help minimize the consequences of encountering isolated deeper instability.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    New snow is expected to drift and deposit into cohesive slabs today along the downwind side of ridgetop areas. New wind slabs are expected at 1 foot deep or less. Fresh surface hoar was reported yesterday around the forecast area. Anyplace new wind slabs deposit on top of this surface hoar could be fairly reactive today, even if the slab isn't very thick.

    Identify areas where blowing and drifting snow is depositing. Use clues such as cornice features, wind drifts, and snow surface texture to highlight areas of concern. Move around these areas with caution. Surface hoar at the old/new snow interface could allow for wider than usual wind slab avalanches.

    (1/22/2024)

    An obvious spot below cornice for a wind slab avalanche to occur.

    Photo: Sierra Avalanche Center

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2.5–3

    We are close to being done with this avalanche problem but we are not....quite....there....yet. The isolated collapse/whumpf and mixed snowpit test results are good reminders of spatial variability and that the snowpack does not gain strength at the same rate in all locations. Areas along the eastern side of the forecast area show the greatest amount of lingering weakness. Isolated failure of weak layers in the lower half of the snowpack could still lead to a large avalanche.

    Most backcountry travelers will not encounter any signs of persistent instability today. On the flip side, if your group triggers an isolated large avalanche things could go bad in a hurry. If you are presented with the luxury of obvious signs of instability such as snowpack collapsing/whumpfing or snow surface cracking, back off of avalanche terrain in the immediate area. The more likely scenario is that things seem stable right up until a surprisingly large avalanche is triggered. Keep your margins of safety wide and precise to minimize the consequences if a large and probably unexpected avalanche is triggered.

Avalanche Discussion

New surface hoar growth was reported to persist upright yesterday across W-NW-N-NE-E aspects in many locations around the forecast area. Today's new snow may bury and preserve this surface hoar as a new weak layer, especially on open slopes. We are not expecting much in the way of problematic instability in wind protected areas on this surface hoar today. This is due to an expected soft and thin overlying slab of just a few inches of new snow despite the upside-down characteristics of today's snowfall. We will then have a few days to determine the extent of potential weak layer burial around the forecast area before future storms further bury/load any newly formed weak layers. As stated above, this surface hoar may contribute to more reactive wind slabs today.

Regions covered