Continental

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Northeast winds were still transporting significant amounts of snow and wind slabs were touchy on lee terrain yesterday. With gusts up to 70 mph overnight on Thompson Pass and strong winds in town, expect wind slabs to remain sensitive. Identifying and avoiding lee terrain and cross loaded features while riding or snowmachining today will be the best method for mitigating the hazard.

  Wind slabs could step down to deeper layers in the snowpack creating a larger more dangerous hard slab avalanche. (See problem 2, Persistent Slab)

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3

  A layer of weak (faceted) snow is still being found in protected terrain and areas that have been loaded by recent winds rather than scoured. The distribution and depth of this 1/26 weak layer is extremely variable due to recent winds stripping certain parts of the snowpack and loading others, but if you have identified the lee terrain where the wind slab problem exists, you have also identified where this persistent slab problem exists. 

  This weak  layer is becoming more of a low likelihood, high consequence problem because of layers of stiff wind slabs that have built up on top of it bridging the weight of users. Staying off large connected faces, using safe travel protocols like spacing out, and riding one at a time are the best ways to mitigate the problem.

  

• 

  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.