Central Sierra Nevada

Problèmes avalancheux

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Very Likely

  Taille

  2–3

  High intensity snowfall and gale force winds will continue to drift and deposit snow into cohesive slabs. Rapid formation of these winds slabs is expected to lead to natural avalanches. The vast majority are expected along the down wind side of ridgetops, in gully features, and on cross-loaded slopes, mainly in above treeline and near treeline terrain. Unstable wind slabs may also exist in some areas below treeline areas today due to the strength of the winds.

  There are a variety of weak layers at all heights in the snowpack, some of which have been dormant over the past couple of weeks. Rapid new snow loading today could reactivate these old snow weak layers and contribute to very large (size D3) avalanches.

  Even if you are traveling in non-avalanche terrain today, natural avalanches that initiate from above could run down into low angle, treed areas. Plan routes carefully with the ability to avoid avalanche run out zones, even when you cannot see them due to poor visibility.

  

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Very Likely

  Taille

  1.5–2.5

  Natural avalanches may also occur today in wind protected areas, including below treeline. The largest storm slab avalanches are expected in locations where the accumulating storm snow has deposit on top of older, weak sugary snow. This old snow weak layer (sugary facets) is weakest on shaded, wind protected N aspects. It has been observed to varying extent across many NW-N-NE aspects at a variety of elevations throughout the forecast area. In some areas it extends to the ridgetops, in other areas the most well-developed weak layer exists in mid-slope avalanche terrain or near the bottom of drainages. Additional weak layers may also form within the new snow as it accumulates.

  Snow surface cracking, snowpack collapse, whumpfing, or recent avalanches in wind protected areas are clues to the presence of this avalanche problem. Keep in mind that if you are triggering collapsing or whumpfing in low angle terrain, it could trigger an avalanche from connected steeper terrain above or to the side that runs down onto you or another party.