Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

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

MODERATE avalanche danger exists on slopes steeper than 35 degrees at all elevations on the NW-N-NE aspects and on near and above treeline E-SE aspects. A combination of wind slabs resting on weak snow, old persistent slabs, and loose snow sluffs represent the main avalanche problems today. Human triggered avalanches could be possible today.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    New snow and moderate to strong southwest winds will form new wind slabs on the near and above treeline NW-N-NE-E-SE aspects today. Wind loading will also add depth and size to the small wind slabs that already existed in those places. A layer of cold, soft, and weak snow resides below these wind slabs. The combination of a weak layer underneath a wind slab will make human triggered avalanche activity possible today. Some wind slabs could reach 1 to 3 ft. in depth in heavily wind loaded areas.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    In areas above 9,500 ft. on near treeline and below treeline NW-N-NE aspects, human triggered persistent slab avalanches could be possible today. Weak layers of well developed facets and depth hoar still remain buried in the snowpack in these areas. With the additional snow and wind expected today the load above these layers will increase and make them more fragile. Since there are very few areas in the forecast area with terrain above this elevation where these conditions exist, this problem remains isolated in distribution.

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Human triggered loose dry sluffs could occur in non-wind affected areas below 9500 ft. on near and below treeline NW-N-NE slopes where cold unconsolidated snow rests on top of a frozen rain crust. These sluffs could entrain enough snow to knock a person over or push them off course into obstacles. 

Avalanche Discussion

Yesterday observations on Red Lake Peak below 9500 ft, in Deep Creek below 8500 ft, and on Freel below 9300 ft, showed up to 16 inches of soft, cold snow resting on top of a thick supportable rain crust. Below this thick refrozen layer some moist unconsolidated snow still remained in the Red Lake Peak area. Above 9300 ft on Freel and on Chickadee Ridge in the Mt. Rose backcountry the rain crust became much thinner, and dry, weak facetted snow grains remained in the bottom part of the snowpack. Data and observations from all of these locations at all elevations showed the cold soft surface snow on the NW-N-NE aspects has very little strength and that it may not support a new snow load very well. Even though some surface hoar existed on the surface in some areas yesterday, no data indicated intact buried surface hoar yesterday.

Some wind transport did occur yesterday, and some small and isolated wind slabs did exist near ridgelines in areas prone to wind loading in Deep Creek, on Red Lake Peak, and on Freel. Some sluffing also occurred on steep slopes in Deep Creek as the soft snow slid downslope on the rain crust. 

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