Continental

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1.5–3

  A prolonged period of dry weather has allowed the snowpack to settle, lowering the likelihood of triggering an avalanche. At the same time, six weeks of cold weather has continued to promote faceting, meaning weak snow remains in the snowpack and the potential for a human-triggered avalanche still lingers in places where a slab overlies facets.

  Unfortunately, recent strong wind events have created a highly variable upper snowpack, making it difficult to describe one setup that users will encounter. Expect to find multiple layers of wind slab with faceted snow in between, with conditions varying significantly by aspect and location.

  In addition to this generally weak and faceted snowpack, we continue to track the 1/26 facet layer. This layer is becoming harder to identify and has shown decreasing sensitivity in recent stability tests. At this point, triggering an avalanche on this layer appears unlikely, but the consequences would be significant if it were triggered. This layer can still be found on all aspects above 1000 feet and is generally buried 2 to 4 feet deep, depending on how much wind slab overlies it. On many windward slopes in Thompson Pass, the overlying slab has been stripped away by strong winds, and this problem no longer exists.

  The 1/26 layer could become reactive again later in the season as temperatures rise or if the snowpack receives a significant new load. Predicting exactly where and when that may happen remains difficult.

  Snowpack assessment should be done on a slope-by-slope basis due to the high degree of spatial variability. Users can reduce their risk by choosing simple terrain and avoiding terrain traps.

   

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Wet loose and other solar-triggered avalanche activity has remained limited so far, but is expected to become more of a concern as temperatures slowly return to seasonal norms. Calmer winds and a slight increase in temperatures this afternoon may allow sunny slopes, especially south- to west-facing terrain, to warm enough for small loose avalanches and other signs of instability to develop. Solar warming may also increase sensitivity at older weak interfaces in the upper snowpack, adding a new form of stress to a snowpack that has seen very little change in recent weeks.

  Watch for moistening surface snow, rollerballs, small loose avalanches, and failing cornices as slopes heat up through the day. If you begin to observe any of these signs, expect hazard to increase with additional sun exposure.

  Please share any observed avalanche activity to help us track how this problem is developing.

   

  

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  2–3

  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.