Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
View on map

Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
Open full map
Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Unstable conditions are ongoing with continued avalanche activity. Numerous avalanche problems arising from wind drifted snow, persistent instability, and snow surface warming will coexist in the backcountry today. Avalanche danger is MODERATE at all elevations.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Unstable wind slabs existed yesterday and are expected again today. Strong SW ridgetop winds have scoured most all snow on the ridgetops available for transport and created wind slabs where this drifting snow has deposited in lee areas. Areas of unstable wind slabs formed in lee areas exist above treeline and near treeline on NW-N-NE-E-SE aspects. Avalanche size is expected at D1 to D2.

    Leeward slopes below ridgetops adjacent to wind scoured areas, slopes below cornice formations, and slopes with new wind pillows are all indications of where unstable wind slabs may be encountered. Identify the areas of concern and move around them with caution. These wind slabs are dense and have increased destructive potential for their size, with smaller avalanches having increased potential for creating injury. These wind slabs may be stubborn and not respond to the first trigger.

     Wind slab avalanche from yesterday on Lincon Ridge (Yuba Pass).

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2

    This avalanche problem has become a somewhat nasty lurker. Unstable snowpack conditions on a weak layer of buried surface hoar are clearly ongoing on isolated slopes around the forecast area. Spatial variability is at play here with weak layer stabilization occurring at different rates in different locations. Isolated persistent slab avalanches failing 1 to 3 feet deep in the snowpack may occur in areas without signs of current instability and with numerous previous tracks. NW-N-NE aspects at all elevations remain suspect. Avalanche size is expected at D2 and the high density of the slab could easily create injury.

    With the variability and isolated distribution, it would be very easy to travel around all day without noticing any indications of instability right up until triggering an avalanche. Avoiding NW-N-NE aspects or using only slopes of less than 30 degrees in slope angle, not connected to steeper slopes above or to the side are the true tools for avoiding this avalanche problem. Heavily treed terrain should be without this avalanche problem, but any open areas within this heavily treed terrain are highly suspect.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    High sun angles and strong incoming solar radiation will create snow surface warming on all aspects today including N. Rollerballs and loose wet avalanches are expected today in wind protected areas on all aspects, especially around exposed rocks. Avalanche size is expected at D1 with an isolated D2 not impossible.

    With fairly clear skies this morning and fairly warm air temperatures last night this avalanche problem is expected to form quickly today. With size D1 avalanches, consequences will come from being pushed into or over downslope terrain features such as rocks, trees, cliffs, and terrain traps. These terrain features could make high consequences from an otherwise small avalanche. Rollerballs and pinwheels are indications that this avalanche problem is present.

Avalanche Discussion

* Yesterday on Lincoln Ridge (Yuba Pass area), a wind slab avalanche with a 1 foot crown was intentionally triggered by cornice collapse on a NE aspect in near treeline terrain. A crack across the bed surface went another 2 feet down to snowpack failure on the buried surface hoar layer that is a part of the persistent slab avalanche problem. Snowpit tests performed earlier in the tour had identified unstable conditions on the 10 mm+ gain size surface hoar layer 1 foot below the snow surface in wind protected areas.

* Fog, mist, and low elevation very light rain yesterday morning created very moist snow surface conditions up to at least 8,000' (and possibly much higher) on all aspects. Wet surface snow was widespread below 7,200'.

Regions covered