Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

Avalanches with serious consequences remain possible today. Slabs of wind-drifted snow could fail in places where wind-blown snow has piled up, and buried weak layers could break and produce surprising avalanches in more sheltered areas. Give this complex snowpack time to adjust, and enjoy the soft winter-like snow on lower-angle slopes not connected to avalanche terrain. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Wind slabs formed on leeward facing NW-N-NE-E-SE aspects during the storm. Triggering a wind slab avalanche will remain possible today, especially on slopes below cornices, in gullies, and on open slopes where wind-drifted snow has piled up. Most of this terrain exists in near and above treeline areas, but a few wind slabs may exist in wind-exposed areas below treeline. The light NE winds overnight may have made some of these wind slabs more cohesive. In areas where the wind slabs rest on top of old weak layers mentioned below, more destructive avalanches with wider propagation could occur.

    Cornices above a slope, snow drifts, and wind-created surface textures can provide clues about where wind slabs may exist, and recent avalanches or cracking in wind-blown snow represent sure signs that those wind slabs remain unstable. If you venture into exposed areas today, gather as much information as possible from small slopes without consequences before even considering larger terrain. Still, unstable wind slabs that fail on the weak layers mentioned below could surprise you by avalanching on a slope with no other signs of instability. 

    (3/29/2023)

    Skier triggered shooting cracks on a wind-loaded slope on Silver Peak.

    Photo: SAC

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Multiple layers of concern ranging from crusts and weak snow at the base of the storm snow to old graupel layers to buried surface hoar exist in the snowpack. Triggering an avalanche remains possible on these layers, especially on NW-N-NE aspects. If one of these layers does break, 2 to 4+ft deep avalanches could occur.  Any steep slopes where these layers exist remain suspect today especially slopes with trigger points like convex rollovers.

    Correctly identifying which slopes may avalanche or which weak layers may fail is difficult. These kinds of avalanches catch people by surprise on slopes they thought seemed stable. Trying to outsmart this problem often results in triggering an avalanche that breaks wider than expected and has serious consequences. Patience and avoidance represent the best tools for dealing with persistent slabs. Give them time, and enjoy the soft winter-like snow on lower-angle slopes not connected to avalanche terrain. 

    (3/27/2023)

    Unstable snowpit test results on a graupel layer 2 feet below the snow surface and adjacent to an avalanche that occurred on March 24. The Nipple, South of Carson Pass, CA

    Photo: SAC

Avalanche Discussion

  • Observers reported recent avalanches in the Blue Lakes area, on Stevens Peak, and along the Sierra Crest at the head of the Pole Creek drainage yesterday. People also triggered shooting cracks on wind-loaded test slopes in these areas yesterday.
  • Snowmobile observations around Blue Lakes found multiple buried weak layers, and tests on those layers produced unstable results. Skiers in the Pole Creek drainage triggered whumps and collapses that failed on crust/facet layers at the base of the storm snow. They also found other buried weak layers, but their snowpit tests did not produce unstable results. Weak layers are now buried at least 1.5 to 3 ft deep in the snowpack and could be deeper in some areas. 
  • While some small rollerballs or pinwheels may form on sunny slopes today, unseasonably cold weather and increased cloud cover this afternoon should prevent widespread wet snow from forming despite the intense spring sun. Sun crusts may exist on sun-exposed E-SE-S-SW-W aspects.

Regions covered