Avalanche forecast

Central Sierra Nevada

Sierra Avalanche Center
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Avalanche danger

Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

CONSIDERABLE avalanche danger exists near treeline and above treeline today. MODERATE avalanche danger exists below treeline. Today's wind slab and storm slab avalanche problems have the potential to be exacerbated by rapid warming. Loose wet avalanches are unlikely today, but could become an issue if the sun comes out from behind the clouds. The avalanche situation could be fairly complex in the backcountry today. If in doubt, seek low angle terrain without steeper terrain above.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1

    New snow combined with strong to gale force SW winds last night are expected to have created new wind slabs near treeline and above treeline on NW-N-NE-E-SE-S aspects. Avalanche size up to D2 is expected (large enough to bury or injure a person). Wind slab instability may be especially problematic today due to two issues beyond the norm: 1) Graupel (pellet snow) was noted in several locations around the forecast area at the onset of yesterday's snowfall. Graupel may be sandwiched at the old/new snow interface between crust below and new wind slab above. In locations where this graupel is a problematic weak layer, it may allow for wider than normal propagation of wind slabs today. 2) Any breaks in cloud cover today will allow for rapid warming of wind slabs that could increase the likelihood of triggering. This potential rapid warming will affect all aspects given the high sun angle this time of year, but would be especially problematic on E-SE-S aspects.

    Look for and avoid areas of concern. Identify slopes similar to any in the area with recent avalanche activity. Identify slopes with signs of recently wind drifted snow including cornice or wind pillow formations across the upper portion of the slope. Look for snow surface cracking. Use these clues to identify the slopes most likely to hold unstable snow and choose different terrain.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    New snow deposited in wind protected areas below treeline may allow for problematic storm slabs on all aspects today. Avalanche size up to D2 is possible (large enough to bury or injure a person). The potential graupel layer and rapid warming issues outlined in the wind slab section may also exacerbate storm slab instability today. Look for signs of recent avalanche activity below treeline and snow surface cracking. Pay attention to sun breaks and associated rapid warming. Avoid avalanche terrain in any locations where signs of unstable storm slabs exist.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1

    Loose wet is an unlikely avalanche problem today, but could be an issue if cloud cover is less than forecast and more sunshine occurs than expected. Pay attention to cloud cover and sun breaks. The more the sun comes out from behind the clouds, the more this will be a problem. Natural or human triggered roller balls will be an indication of a developing loose wet avalanche problem today. If this avalanche problem materializes today, avalanche size up to D2 could occur on any aspect at any elevation (D2 = large enough to bury or injure a person).

Avalanche Discussion

* New snow last night will have been deposited on top of either melt-freeze crust or wet snow on all aspects throughout the forecast area. Graupel was noted at the start of the storm in several locations. At this time there are no weak layers of concern below the old/new snow interface.

* The high sun angle this time of year allows for significant amounts of incoming solar radiation on NW-N-NE aspect terrain that is otherwise well shaded from November through February.

* Snow cover below 7,200' to 7,500' is becoming very thin to nonexistent in many portions of the forecast area. In some locations, snow cover is notably patchy below 8,000'. There area some areas of exception where better snow cover exists at these elevations.

Regions covered