Eastside Region

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  New snow and extreme winds have created fresh wind slabs near and above treeline. Watch for blowing snow and signs of instability, such as recent avalanche activity and cracks shooting out from your skis or board through dense, textured, or hollow-sounding snow. Be wary of terrain features that promote drifting, such as the leeward side of ridgelines, alpine couloirs, mid-slope convex rollovers, and cross-loaded depressions.  Expect the size and distribution of unstable slabs to increase as you move towards the Sierra crest and gain elevation.

  

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Soft, cohesive slabs of recent snow are likely in steep, sheltered terrain. Convex rollovers and confined terrain features like chutes and gullies are most concerning. Be cautious on or under steep terrain over 30° today and be cognizant of your exposure to terrain features that increase the consequences of avalanches. This includes road cuts, gully features, cliff bands, and mid-slope depressions. Snowfall will taper off this morning, and the recent snow will become less sensitive throughout the day.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Old, weak, faceted grains that formed on the surface during our dry period in January have been buried by several storm systems over the last couple of weeks. Recent field observations have noted poor structure at this interface and signs of instability, such as shooting cracks and audible collapsing in the snowpack. While no avalanches breaking in the old snow have been reported, we have just added a significant load of heavy, wet snow.  A relatively small wind or storm slab avalanche or the weight of a skier might be all that is needed to trigger a larger and more destructive avalanche breaking in old snow layers. These will most likely be on sheltered northerly aspects near the treeline. Remember that Persistent slab avalanches can be remotely triggered from adjacent slopes and flat terrain below a steep slope and, if triggered, can propagate across and around terrain features that would otherwise confine new snow instabilities. Build wide safety margins into your tour plan and use conservative terrain choices and careful route finding to limit exposure.