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

Early this morning, LOW avalanche danger exists for all elevations and aspects. Areas of MODERATE avalanche danger are exected to form at all elevations on SE-S-SW aspects on slopes 35 degrees and steeper in response to daytime warming. Isolated areas of loose wet instability may occur on W-NW-N-NE-E aspects as well.

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Despite the cloud cover, areas of loose wet instability are expected to form today mainly on SE-S-SW aspects as daytime warming progresses. Lesser amounts of snow surface melt and subsequent instability are expected on W-NW-N-NE-E aspects today. A few isolated areas have made the full transition to "corn snow" where surface wet snow will exist on top of thick melt-freeze crust during much of the day's melt cycle. However in the vast majority of areas, this full transition has yet to occur and surface wet snow will be found on top of drier remnant storm snow. In these more unstable areas, no significant crust exists at the base of the wet surface snow during the majority of the melt phase. This wet snow over drier remnant storm snow is prone to human triggered loose wet avalanche activity.

    Use clues such as human triggered roller balls and pinwheels approaching or exceeding 1 foot in diameter and/or boot top depth penetration into wet snow to determine when critical amounts of surface wet snow exist. When these clues are observed, move to lower angle slopes of less than 30 degree slope angle without steeper terrain above or change to a less sun exposed and more frozen aspect.

Avalanche Discussion

Observations made yesterday on the S-SE aspects of Mt. Judah (Donner Summit area) revealed deep wet snow and signs of loose wet instability below 8,000' by 11 am. Deep boot penetration into surface wet snow, skier triggered roller balls, and tiny skier triggered loose wet sluffs were observed in the area. Ridgetop winds were creating convective cooling that kept the snow surface frozen near ridgetop level while significant melt was rapidly occurring 100' to 200' below. Snow surface melt was significantly slower to occur on W and N aspects as is typically the case. Several creek beds at mid slope level were observed as open and flowing, indicating fairly well established free water drainage from the snowpack.

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