Central Sierra Nevada

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1.5–3

  Wind slabs formed during the storm will remain fragile today. Venturing onto steep wind-loaded slopes would likely trigger an avalanche. The largest wind slabs lurk near and above treeline on NW-N-NE-E-SE aspects, but some wind slabs may exist in open areas below treeline due to the strength of the winds. Moderate amounts of blowing snow today will keep adding to these wind slabs. Large wind slab avalanches remain likely. 

  Watch out for areas near ridges, open wind-exposed slopes, and gullies where wind-blown snow piles up. Cornices and blowing snow along a ridge indicate that the slope below is wind-loaded. Recent avalanches and cracking in the snow represent sure signs that wind slabs remain unstable. It makes sense to step back and give wind-loaded areas a wide berth today. Traveling in terrain sheltered from the winds should also provide better snow quality.

  

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2.5

  Storm slab avalanches and sluffs of dry loose snow occurred yesterday and remain possible today. Cold weather means light snow but slower consolidation in the storm snow. Soft slabs of storm snow could fail on lingering storm snow weaknesses like graupel layers, especially where the storm snow has stiffened or been touched by below-treeline winds. These could involve more than enough snow to bury or injure a person since they could entrain all the storm snow. Some of the sluffs of storm snow could also entrain enough snow to cause problems. Unstable storm slabs could exist on any steep slope. 

  Assess the potential for storm slabs before committing to a slope. Identify where unstable storm snow lingers by getting out of existing tracks to look for cracking in the storm snow and feeling for different layers of snow as you travel through the terrain.  If you see any signs of storm snow weakness or doubt a slope's stability, bypass that area for somewhere without signs of instability. 

  

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3.5

  This storm has added another large load to the facet/crust layer (Feb 21 weak layer) buried 6 to 8+ feet deep in the snowpack on NW-N-NE aspects. The new load had the potential to overload this layer and cause wide, deep avalanches. The most likely time for this layer to fail was yesterday during the storm's peak. Still, an isolated deep avalanche may remain possible today as the snowpack adjusts to the added weight of this storm's snow. The possibility exists that other large triggers like avalanches or massive cornice failures may break this layer. The resulting avalanches would be wide, deep, and likely unsurvivable if this layer fails. As the new snow consolidates, these avalanches will become more isolated and difficult to trigger. 

  Patience and avoidance are the only good ways to deal with this avalanche problem. Give those steeper lines some time and choose lower-angle terrain that cannot produce deep avalanches to reduce exposure to this problem. Remember, avalanches that fail deeper and wider than expected have a greater chance of catching more than one person.