Continental

Lawinenprobleme

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  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  1–2

  Light to moderate south winds have been occurring over the last couple days as skies have cleared.  During last weekends storm loading patterns show signs of stronger southeast-east winds.  The degree and duration is unknown though as multiple wx stations at and near Thompson Pass were not working during the event.

  Slightly wind affected snow has been reported and observed above 3000' with a few natural avalanches observed below ridgelines on NE-NW aspects.  Today it will be possible to trigger wind slabs 1-2 feet in depth on northerly aspects below ridgelines and in wind channeled terrain.  Watch for signs of recent wind slab development such as pillowed slopes and hard snow over soft at the surface.  On 2/14 wind affected snow did not show signs of instability, however, human triggered avalanches are expected to be possible in specific locations such as in steep terrain below high elevation ridgelines where mild active wind transport was continuing to occur yesterday.  

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  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  2–3

  On 2/14 new snowfall from last weekend was reported and observed to lack signs of instability with snowpits pointing to good bonding with stable results and good structure in multiple locations on the north side of Thompson Pass.  This is all positive information but more data needs to be gathered from other locations before we can begin to list this problem as unlikely.  New snow was deposited on facets (weak snow) in most locations and the depth of new snow is a cause for concern, due to the size of avalanches that would occur if a person were to trigger a slide.

   In some locations, the 2/9 facets existed above a hard bed surface of old windblown snow created by the outflow winds at the beginning of the month.  In other areas that were previously protected this hard bed surface does not exist. We may be in a situation where signs of instability are not present due to the depth of the new snow, even though a potentially weak layer may exist.  A lack of  avalanche activity in the Thompson Pass area indicates that this weak layer did not cycle naturally and is now buried in our upper snowpack.  

  Further assessment of this situation is necessary.  Use terrain progression today along with ECT tests to assess snowpack stability.   Terrain progression is a process of starting on smaller slopes with low consequences to assess stability and slowly moving towards steeper terrain only once good stability can be confirmed.  At this point, human triggered avalanches that do occur would probably be initiated from steep terrain (>35°) and/or unsupported slopes.  

   

  

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  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  1–2

  Temperatures above freezing are once again forecasted for coastal locations.  Wet loose natural activity is expected during the heat of the day below 4000' on southerly aspects.  This activity will begin where rocks or vegetation exist as the sun's heat is more readily absorbed in these areas and transferred into the surrounding snowpack.  If you choose to travel on southerly aspects today pay attention to the effect the sun is having on the surface snow.  Is the surface becoming moist?  Is this wet snow more than a few inches deep?   If the answer is yes, then avoid traveling on and exposing yourself to steep solar aspects.  Even small avalanches can have the power to knock you off your feet or bury you if you are in a terrain trap.