Continental

Problèmes avalancheux

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Likely

  Taille

  1–2.5

  Northeast winds quickly ramped up yesterday morning and redistributed soft snow at the surface into wind slabs in specific terrain.  This wind event was brief, with a decrease in strength and distribution observed by the late afternoon.  The depth, hardness, and distribution of fesh wind slabs will vary depending upon location.  In terrain that is close to the Thompson Pass Gap, expect to find deeper wind slabs(1-2') that are stiffer and have a wider distribution across the terrain.  Stiffer and deeper slabs may be more stubborn to triggers but will have the ability to propagate greater distances if initiated.

  In more protected terrain, wind slabs will be thinner(~6-12 inches), softer and confined to pockets in cross loaded gullies, lee sides of terrain features, and just below high elevation ridge lines.  These softer slabs may be easier to trigger than the harder slabs but could be more pockety in nature, depending on the terrain involved.

   North wind is expected to continue through wind channeled terrain, but is expected to be significantly lower in strength and distribution. Pay attention to what direction the wind was blowing previously and which slopes would be loaded.  Jumping on small inconsequential test slopes that were previously loaded by wind can help get an idea of depth and sensitivity of wind slabs in the area you choose to travel. Watch for shooting cracks or collapses, indicating the snowpack has the energy required to produce an avalanche.

  Better stability and riding quality can be found in areas protected from the most recent wind.

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Likely

  Taille

  1–2

  Wet loose avalanches will become likely today on solar aspects that are receiving direct solar input.  6-12 inches of new snow arrived on 3/5-6, that will likely produce wet loose activity on steep sunny slopes, especially in areas that were not affected by yesterdays wind.

  Pay attention to aspect and keep in mind that wet loose activity will often peak when the sun is perpindicular to a slope.  Low elevations will be the most affected by this problem, but this is the time of year when high elevations will become reactive on the steep rocky terrain that funnels into a lot of our upper elevation North facing ramp terrain.  Keep in mind this is our first day of sun after a moderate precipitation event and the sun has some power this time of year.  

  The size of wet loose avalanches is directly correlated with the size of the slope, its shape (does it funnel or fan out?), and how warm the snow is.  Think about the combination of all of these factors when moving through terrain exposed to steep solar aspects.

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Possible

  Taille

  1.5–2

   

  There are currently 2 persistent weak layers on our radar, both are believed to be limited to terrain below 3000'.   There is a layer of buried surface hoar from Valentine's Day as well as weak snow below a decomposing rain crust from late January.  Additional snow and wind loading are slowly adding stress to these layers where they exist.

   Buried surface hoar from 2/14 exists in previously wind-protected areas from 1500 -2500 feet.  This layer is difficult to identify as it has only been found in a narrow elevation band and exists in terrain that was protected from the strong outflow (North) wind event that occurred in late January.  This layer has been found on average between 12-20 inches in depth.  Where this layer is well defined, propagation in ECT tests has been observed as recently as 3/6.

  Below 1500 feet, a rain crust is buried 16-20 inches and has shown propagation beneath the crust in snow pits as recently as 3/5.  Due to the low elevation, this is only a concern in a limited amount of terrain.  This layer could be a concern in steep low elevation canyons, or on steep unsupported slopes below 1500'.  Use caution when traveling through low elevations with poor snowpack structure. 

   To limit exposure to both of these layers avoid terrain traps and consider using conservative terrain while moving through low elevations..  There is uncertainty about the current and future reactivity of these two layers.  There have not yet been any observed or reported avalanches on either of these layers.  We are keeping these on our list, as current weather conditions will continue to stress these layers.