Continental

Lawinenprobleme

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  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  1–2

  North winds increased overnight and are expected to remain strong through the day. Expect continued gouging of the snowpack on windward slopes and ongoing wind slab development on lee aspects. Recent reports and observations show that the most recent wind slabs have not fully stabilized, and there is still some snow available for transport. This means specific lee terrain will remain sensitive to human and machine triggers, with slabs 1–2 feet deep possible today.

  After multiple rounds of strong wind with small pulses of snow in between, the upper snowpack has developed a layered, “stacked” wind slab structure. In some areas, weak faceted snow has been found beneath older wind slabs, which could allow avalanches to fail at a variety of depths and sizes.

  In addition to the fresh wind slab problem, a layer of weak snow remains buried 2–3 feet deep (see Problem 2). In isolated areas, a wind slab avalanche may step down into this layer and produce a larger, more dangerous avalanche. The distribution of this deeper weak layer has become more variable, as many windward slopes have been stripped of the overlying slab.

  

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  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  2–3

  We continue to see propagation in stability tests failing on the 1/26 facet layer. Although this weak layer is producing unstable results in snowpits, it is now capped by very hard, wind-compacted snow, making it harder for a person or machine to trigger. We have kept the likelihood at Possible today because active wind loading is adding stress to lee slopes.

  If triggered, this layer has the potential to produce large, destructive, widely propagating hard slab avalanches that would be difficult to survive.

  The best way to reduce risk is to avoid complex terrain, including large connected alpine faces. Conservative terrain choices remain important today, as persistent slab avalanches can break wider and farther than expected.

  

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  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Unlikely

  Größe

  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.