Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

The avalanche danger will increase to CONSIDERABLE on near and above treeline NW-N-NE-E-SE aspects 35 degrees and steeper by this afternoon and evening. Human triggered avalanches will become likely as new wind slabs will form on these slopes. MODERATE avalanche danger will form on the remaining aspects and elevations where avalanches could take the form of loose dry instabilities or isolated storm slabs by later this afternoon. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    As new snow and strong southwest winds impact the forecast area today, new wind slabs will develop on the leeward aspects in near and above treeline areas. These wind slabs will accumulate above a variety of snow surfaces ranging from wind scoured surfaces to melt freeze crusts to old hard wind slabs and will likely accumulate more quickly than they can bond to themselves or some of the old snow surfaces. Human triggereing of these wind slabs will become likely today.  By this afternoon wind slabs could reach 1-3 ft in thickness in heavily wind loaded areas. The majority of avalanches resulting from the failure of these wind slabs should fail at or above the old snow surfaces; however, they could break into older snow layers in areas where the wind slabs form on top of old hard slabs left over from previous wind events and storms. The most sensitive wind slabs will exist on wind loaded N-NE-E aspects and cross loaded NW and SE aspects in near and above treeline terrain. These wind slabs may extend into more sheltered areas as well given the strength of the winds.

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Some small loose dry snow sluffs may start to occur by this afternoon and evening as cold new snow falls onto frozen melt-freeze crusts and other old snow surfaces. If more snow falls than forecasted some small storm slabs may form as well. Near and below treeline NW-N-NE-E aspects sheltered from the winds hold the best potential for these kind of instabilities since they had more previous snow coverage. These instabilities could also form on other near and below treeline aspects where previous snow cover exists, but they will be more isolated on the SE-S-SW-W because the previous snow cover has melted away from most of these aspects. As more snow accumulates tonight and tomorrow these loose dry instabilities may give way to small storm slabs. 

Avalanche Discussion

Most recent observations from around the forecast area have indicated a strengthening trend in the snowpack and a great deal of variability in snow coverage and snow surface conditions. Melt-freeze crusts exist on sun exposed aspects, scoured surfaces remain on exposed near and above treeline N-NE-E aspects, and some pockets of soft unconsolidated snow remain on sheltered and shaded northerly aspects. Yesterday on Carpenter Ridge, similar variable conditions existed. Most of the observations from this area yielded data consistent with an overall strengthening trend except in places where a hard wind slab existed on top of looser weaker snow layers. These hard slabs remained isolated in distribution and small in size, but all the data collected about them indicated that additional snow loading could cause them to fail. 

Regions covered