Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

A weak snowpack continues to exist throughout the forecast region.  Consequences of being involved in an avalanche are elevated due to the exposed rocks and early season conditions.  Look for signs of instabilities and move away from avalanche terrain if you see or experience unstable snow.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Our weak faceted snowpack continues to be the main avalanche concern.  The most recent storm snow has not been enough load to cause avalanches on this weak layer up to this point, with a high level of variability in the weak layer and overlying slab strength depending on location.  Snowpack tests continue to show weakness and unstable results on these well developed weak layers.  Any avalanche involvement with this persistent slab problem could have high consequences of trauma due to our rocky and early season conditions.

    Managing a persistent slab avalanche problem is difficult.  Our early season conditions make it that much harder as this problem exists in most of the areas with usable snow for recreation.  Signs of unstable snow would be shooting cracks, collapsing, and whumpfing sounds.  Utilizing non-avalanche terrain well under 30 degrees in steepness with no overhead hazards is a great strategy to minimize this persistent slab avalanche problem.

    Weak, sugary grains at the bottom of the snowpack .  Carson Pass area.

    Photo: SAC

Avalanche Discussion

A weak faceted (sugary) snowpack exists on most NW-N-NE aspects.  At lower elevations, faceted snow exists in between rain crusts.  Above around 8,500', rain crusts disappear, or are decomposing, and the snowpack becomes nearly all weak faceted snow. Generally speaking, the higher up you go on wind protected NW-N-NE aspects, the weaker the snowpack.  These weak layers are well developed, with depth hoar found in many areas near the base of the snowpack.  Early season NE wind events previously scoured some exposed slopes down to dirt, rock, or ice-leaving weak faceted snow mid-slope and below.  The distribution and strength of the faceted snowpack varies throughout the forecast region.

Cold temperatures, clear skies, low sun angles, and long nights will continue the faceting process in our shallow snowpack further decreasing the snowpack structure.

There is still the potential to hit many obstacles (rocks, logs, open water, bushes, etc.) that are barely covered (or not) by the shallow snowpack. Areas with a supportable mid snowpack rain crust in the 7,500’ to 8,500’ elevation range provide the most usable snowpack. Anticipate encountering a different snowpack structure and a different set of travel conditions if you are moving from one place to another around the forecast area.

Regions covered