Continental

Avalanche problems

• 

  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 but high-consequence problem most likely to be triggered 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.  

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  North winds have ramped up once again in response to a low pressure system in the Gulf, which brought a trace to 6 inches of new snow across the forecast area over the last 48 hours. Fresh wind slabs are expected to be forming today, and it will be possible for a person or machine to trigger them on recently loaded slopes. These slabs will likely be up to 1 foot deep.

  Prior to this latest round of snowfall, the snowpack was already heavily wind damaged, with stripped and scoured surfaces on windward slopes and older, stubborn wind slabs on lee slopes and in cross-loaded gullies. Today, new deposits of wind-drifted snow will be building on top of these older wind-affected surfaces, creating fresh slabs that may be more sensitive to triggers than the snow beneath them.

  The most likely places to find unstable wind slabs will be on lee slopes, cross-loaded gullies, below ridgelines, and around convex terrain features. The best way to manage this problem is to anticipate where snow is actively being deposited and avoid those slopes. Small, low-consequence test slopes can provide useful feedback, but they should not be used as proof that bigger terrain is safe.

  In isolated areas, a wind slab avalanche could step down into deeper weak layers in the snowpack, particularly north of Thompson Pass (see Problem 2).

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  1.5–3

  We have been in a period of low stress and little avalanche activity involving our persistent weak layers. This is becoming a low-likelihood problem, but it may still be possible to trigger an avalanche in isolated areas where the snowpack is thinner and weaker, especially in the northern end of the forecast area.

  These weak layers remain buried 1–3 feet deep in many locations and have not gone away. While they have been quiet recently, they could become active again with additional loading from new snow, wind, or warming temperatures.

  In the meantime, careful terrain management remains important. Pay extra attention to thinner snowpack areas and consequences of being wrong, as persistent slab avalanches can remain dangerous even during quiet periods.