Maritime

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1.5–2.5

  Avalanche conditions will remain similar to yesterday. Light to moderate snowfall will continue to add load and build slab depth over weak snow. Dangerous avalanche conditions exist. Human-triggered avalanches are likely, and could be 1–2+ feet deep. In steep, rocky terrain and in areas with a thinner snowpack, avalanches may step down into deeper weak layers in the snowpack (see Problem 2).

  On the north side of Thompson Pass, 1-2 cm buried surface hoar over a rain crust continues to be found up to 3000’. In most areas we’ve observed, the buried surface hoar has been flattened/laid over, except north of our Continental zone, where it has remained more intact. As the slab above this layer stiffens and thickens, expect longer propagation and the potential for larger, more connected releases. A few small natural avalanches have recently been observed on steep rollovers in the Python Buttress area. In the Maritime zone, buried surface hoar is no longer widespread due to warm temperatures and rain.

  Above 3000’, buried surface hoar has not been identified, but a reactive interface exists. On 2/6, two separate skier-triggered avalanches at upper elevation propagated widely for the terrain and resulted in full and partial burials on different aspects. See the Observation section for details.

  Travel advice: The best way to manage this problem is to avoid complex terrain and slopes steeper than 30°. Both incidents occurred with no obvious warning signs beforehand. Snowpits are not a reliable assessment tool for this problem—small differences in slab thickness or stiffness can greatly change sensitivity.

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Temperatures are trending down, but are still expected to be above freezing with more rain possible today.   Wet loose natural and human triggered avalanches will be a concern today in steep low elevation terrain.  Pay attention to surface conditions.  If wet snow exists at the surface then wet loose avalanches are a concern in terrain steeper than 30°.  Be aware that even small wet loose slides can be powerful and can knock a traveler off their feet or machine.  Pay attention to not only the slope you are traveling on but what is above and below you.  It is reccomended to avoid terrain traps and steep terrain at low elevations today.

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  2–3

  A deeply buried weak layer near the ground remains a concern, especially in steep, rocky terrain and areas with a thinner snowpack. Triggering this layer is unlikely for most travelers right now, but if it does fail the result would be large, destructive avalanches with severe consequences.

  This problem is most likely to show itself where the snowpack is shallow or variable around rock outcrops, scoured features, convex rollovers, and ridge tops. The likelihood may increase over time with additional loading from new snow and wind, or with warming from the sun in the future.

  Travel advice: Avoid committing to big, consequential terrain where a deep release would be unsurvivable. Choose routes that minimize time spent under overhead start zones and avoid thin, rocky trigger points.