Continental

Avalanche problems

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Our area received 8–12 inches of new low-density snow. Yesterday, this new snow was found to have a sensitive density change near the old snow interface. Hand shears repeatedly produced failures on isolation, and numerous small avalanches and cracks were observed on convex terrain features steeper than 30°. Despite this clear instability, the slab still had relatively little cohesion.

  We expect this problem to become more sensitive today as the new snow settles, gains cohesion, and is affected by rising temperatures.  Any areas that have been stiffened by wind will be especially sensitive.  Watch for signs of instability such as shooting cracks and collapsing, and move to lower angle terrain when they are present.  Test slopes will be a useful tool for assessing the sensitivity of the new snow, but they will not effectively provide information about weak layers buried deeper in the snowpack (see Problem 2).

   

   

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3

  The 1/26 layer of faceted snow that we have been tracking for the last month and a half continues to show energetic results in stability tests, with high propagation potential and clean shears (Q1). The likelihood of triggering this layer has decreased as knife-hard wind slabs now cap the weak snow in many areas, and make it more difficult to trigger.

  Users should be aware that new snow has added stress to this setup, and it is still possible to trigger a hard slab avalanche 2–4 feet deep. New snow has also masked older wind textures, making it harder to tell which slopes were previously wind loaded and which were stripped. This is a difficult avalanche problem to assess. Obvious signs of instability may be absent, and the 1/26 layer can be missed in snowpits or misinterpreted by both casual users and experienced professionals.

  The best way to reduce risk is to avoid complex terrain, including large connected alpine faces. Traveling one at a time through avalanche terrain, watching your partners, and maintaining clear communication are always important, but they matter even more when a persistent slab problem exists.

  

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  2.5–3.5

  Weak snow near the ground is increasingly common as you move North through our forecast zones, with the Continental zone being the most concerning. Although it still remains unlikely to trigger this layer, areas that have been scoured from strong northeast winds now have a shallower snowpack making this layer closer to the surface and potentially easier for a rider to trigger.

  This is a low-likelihood, high-consequence problem—especially in steep, rocky terrain and areas where the snowpack is thin or scoured. Triggering this layer directly is unlikely at this time, but avalanches that start in the upper snowpack could step down to the basal weak layer.  There is a high degree of uncertainty regarding the poor structure at the base of the snowpack.  What we can be sure about is that this layer is less of a concern in the Maritime zone and more of a concern as you move towards the Continental zone where the snowpack is thinner and the weak layer is more developed. 

  Watch for thin spots near rock outcrops, scoured features, and along ridge tops. Wind loading adds stress to these shallow areas, and we don’t know where the tipping point is.