Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
View on map

Avalanche danger

Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
Open full map
Out of date — this forecast expired 7 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Warming temperatures, intense snow and rain, and strong winds have resulted in HIGH avalanche danger in near and above treeline terrain and CONSIDERABLE avalanche danger in below treeline terrain. The backcountry will hold a complex mix of wind slab, storm slab, and loose wet avalanche problems today.

Dangerous avalanche activity is very likely today. Travel in, near, or below avalanche terrain is not recommended.   

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2

    Strong SSW and S winds and heavy snow have built new slabs of drifted snow on traditional leeward aspects and in some unusual places. These wind slabs rest on top of lighter snow that will not support them and they will continue to grow in size and extent as more snow and wind impact the forecast area today. Natural and human triggered wind slab avalanches will be very likely today. Wind slab avalanches could be large and destructive (D2-D3). In addition to entraining enough snow to have serious consequences for anyone one caught in an avalanche, the numerous obstacles present in the early season snowpack would make matters even worse. 

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    A warming storm means the snow gets heavier on the surface than below. The new heavy snow is also accumulating on top of lighter old snow. Heavy snow on top of lighter weaker snow represents a great recipe for a storm slab avalanche problem. Slabs of new snow may fail within the storm snow or at the old snow / new snow interface. Human triggered storm slab avalanches will be likely today. These avalanches could involve enough snow to bury or injure a person (D2). Rain falling on snow could also trigger storm slab avalanches and they could entrain wet snow at elevations near or below snow line.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    At lower elevations where rain falls on existing snow, expect to see loose wet avalanches. Most of these should remain small but any avalanche could have consequences since collisions with barely covered or exposed rocks, stumps, and other obstacles would be inevitable. Rain could also trigger the storm slabs or wind slabs mentioned above especially if snow level climbs higher than forecasted. 

Avalanche Discussion

* Observers reported that the snow remained light and cold prior to the onset of this storm. The snowpack had a high degree of variability in coverage and many shallowly buried and exposed obstacles still existed.  

* Some cracking occurred in wind-loaded areas near Carson Pass yesterday. 

* In areas where a thin layer of snow existed from Nov. 20, a thin weak layer now exists at the base of the snowpack. While this layer is not very widespread or continuous in most places, some signs of instability like whumpfing in sheltered areas in the Mt. Rose backcounrty and an isolated unstable test result on Carson Pass were noted yesterday. 

Regions covered