Central Cascades

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Wind slabs will continue to build overnight on lee terrain features as the southwest wind moves the cold light snow. Wind slabs are most sensitive to triggering when they are fresh and we could find these to be easy to trigger on Thursday. 

  We may not see a lot of blowing snow on Thursday as the wind speeds back off, but the existing wind slabs can still be triggered. Steep convex rolls at and below ridge tops will be likely places to trigger a wind slab. As wind moves snow across open slopes, gully features in particular can become 'cross loaded' and filled in with new wind slabs. There can be a lot of variability associated with this problem; some lee slopes will have shallow windslabs while other slopes will collect a lot of blowing snow creating much deeper slabs. 

  Cracking in the wind deposited snow and recent avalanches are good indicators that you can trigger an avalanche. Wind slabs can be avoided by sticking to sheltered areas or slopes that have been scoured by the wind. 

  Wind slab avalanches have the potential to "step down" into the persistent weak layer and create much larger avalanches on west, north, and east facing slopes. 

  Use carefull evaluation in areas of sparse trees, clearings, and sections of dead forests. Open areas 'below treeline' can get enough blowing snow to create wind slabs.

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–2.5

  As the January 31 weak layer of faceted snow becomes deeper, we will will be less likely to get feedback in the form of cracking, collapses, and whumphs. Triggering an avalanche on this layer will be unpredictable and therein lies the tricky nature of a persistent slab problem. Weak faceted snow can be found 2 - 2.5 feet below the surface but that will vary across the terrain. On wind loaded slopes the weak layer will be much deeper. The "possible" rating should not be taken likely. Triggering an avalanche on the Jan. 31 weak layer will result in large avalanches. Non event feedback should not give you confidence. This is not the kind of situation where avalanches will be triggered everywhere. Specific spots in the terrain where we can impact the weak layer will be the culprit. Oh yeah....did I mention this will be unpredictable?

  Shallow rocky areas are trigger points that can bring the weak layer closer to the surface and thereby making an avalanche more easily triggered. Managing a persistent slab problem is easy.....avoid avalanche terrain. It is also worth digging into the snowpack to check for this weak snow on southwest and southeast facing slopes before riding in steep and consequential terrain.

   

• 

  Loose Dry

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–1.5

  Surface snow will remain cold and will have very little cohesion. Dry loose avalanches are possible in steep terrain. These avalanches will mostly be small but they can still be dangerous especially on long sustained steep slopes and around terrain traps. Keep an eye on the terrain below you. Getting pushed down steep slopes, over cliffs, or into rocks can make small avalanches lead to a bad outcome. Loose dry avalanches can happen anywhere the recent snow has not been stripped away by the wind.