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 at all elevations due to lingering wind slab and deep slab avalanche problems. Large destructive slab avalanches remain possible in isolated areas. Small loose wet avalanches may occur today in steep terrain.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Lingering instability of wind slabs continues near treeline and above treeline on NW-N-NE-E-SE aspects. Large triggers such as natural or human triggered cornice collapse are the most likely way for avalanches to occur today. Large overhanging cornices were fairly weak yesterday and may remain so today. Avalanche size up to D2 is possible (large enough to bury or injure a person).

    Keep a wide margin of safety on slopes below or adjacent to cornice features or wind pillows. Stay well back from overhung cornice edges along ridgelines.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    Lingering avalanche concerns associated with deeply buried surface hoar and crust/facet layers have now been combined into a single deep slab avalanche problem as the travel management has become the same. In most areas, these weak layers exist 4 to 6+ feet deep in the snowpack but can be found a shallow as 2 feet deep in some areas. Weak layers associated with this avalanche problem are found both above and below treeline on NW-N-NE-E aspects. Triggering is difficult but consequences are big with large destructive avalanches up to size D4 possible (large enough to destroy a railway car or several buildings).

    Conservative terrain choices are the way to go here in order to manage deep slab uncertainty. Slope scale stability evaluation is difficult as the weak layers are hard to assess so deep in the snowpack. Snowpit tests can give false positive results on deep layers. Previous tracks give no stability indications when dealing with deep slabs. Deep slab avalanches often occur on slopes with numerous previous tracks on them. Choose simple terrain that is not capable of producing large avalanches. Avoid complex terrain around rocks and cliffs and slopes with adjacent avalanche paths that share a runout zone.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Small loose wet avalanches may occur today in steep terrain on any aspect at any elevation. Use roller balls as a clue for the presence of this instability. Avalanche size is expected to be too small to bury a person (size D1).

Avalanche Discussion

* Foggy conditions yesterday morning turning to light rain below 9,000' to 9,500' will have wetted the snow surface in most locations.

* Wind slabs less than one foot deep were noted in several locations yesterday. Triggering was stubborn with small avalanches triggered by cornice collapse.

* Buried surface hoar was noted 2 feet below the snow surface on Carson Pass and 4.5 feet below the snow surface on Incline Lake Peak (Mount Rose area). In both locations, snowpit tests indicated that this layer was difficult to collapse, but still capable of propagation.

Regions covered