Continental

Problemas de aludes

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta montaña
  • Límite del bosque
  • Bajo el límite del bosque

  Probabilidad

  Likely

  Tamaño

  1.5–2.5

  North winds ramped overnight into the mid 50's with gusts to 78 mph recorded at Thompson Pass.  This outflow event is expected to be short lived with strength alredady showing a weakening trend among multiple weather stations.  With the significant amount of snow available for transport, expect to find wind loaded slopes to be sensitive to human triggers up to 2 feet in depth.

  Wind slabs are the most sensitive while they are forming and directly after, which will be the case today.  Being able to identify wind slabs visually and by feel, and anticipate what slopes are loaded is important in avoidance of this avalanche problem.  Pay attention to the wind direction that is/has occurred in the area you are traveling.  Clues like fresh wind lip formation that points towards loaded slopes and eroded snow faces that point towards where the wind is coming from can help with anticipating what slopes are loaded.  The general direction forecasted is North, althogh the direction of valleys and terrain has a big influence on wind direction.  Visual clues will also be present, wind loaded slopes may have a fat pillowed look to them or a rippled texture.  Finally the feel of a wind slab will vary by how old it is.  Today they will be fresh and probably still fairly soft, but still stiffer at the surface than the snow beneath.

  Pay attention to the degree of wind loading in the area you choose to travel as well as the depth and sensitivity.  Small test slopes are a great way to test this.  Watch out for signs of instability such as shooting cracks, collapsing and active wind loading.  

  Wind slabs that are triggered will have the potential to step-down to the interface of the storm snow and old snow and produce deeper more destructive avalanches (see problem 2).

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta montaña
  • Límite del bosque
  • Bajo el límite del bosque

  Probabilidad

  Possible

  Tamaño

  1.5–3

  The 2/20-22 storm cycle left us with 2-3 feet of settled snow and a widespread natural avalanche cycle on 2/22.  This cycle was triggered by intense snowfall rates and strong southerly winds at the tail end of the storm.  Some naturals had very wide propagations associated, which indicate surface hoar that formed during the clear weather of 2/14-16 were buried intact in isolated locations and acted as a weak layer.  Other naturals were simple overloading of the upper snowpack by snow and south wind (direct action avalanches).  Surface Hoar is expected to be varied in its distribution which will make stability assessment challenging moving forward.

  The 2/20-22 storm has now had 2 1/2 days of settlement time decreasing the chances of triggering the ~2 feet of settled storm snow in most areas.  Human triggered avalanches remain likely in isolated areas where surface hoar that was buried on 2/17 exists in the upper snowpack.  This problem is much more difficult to assess than wind slab or storm slab as the distribution of the layer is spotty and may not give signs of instability until you hop on the slope and trigger an avalanche.  

  This weak layer will exist in wind protected basins above 2500'.  Below 2500' rain on snow at the beginning of the storm will have removed this layer.  Better stability has been observed and reported below 2500' as storm slabs are shallower and well bonded to the rain crust below.

  Digging snowpits and having an understanding of what areas are typically wind protected are the best ways to identify this problem.  Realize that digging snowpits can often give confusing or misleading results.  These should be used to tell you where not to go.  A lack of results in one pit is not sufficient information to expose you or your group to consequential avalanche terrain.  This type of avalanche problem takes much longer to heal than a typical storm slab.  More information will need to be gathered to better understand distribution and sensitivity.