Continental

Avalanche problems

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Over the last 5 days, multiple weak storm systems have deposited a few inches at a time to our forecast area, with higher amounts towards the coast.  This new snow is incrementally loading a layer of surface hoar that was first buried on 3/9.  The distribution of this layer is spotty depending upon wind disruption before burial, but seems to be more concentrated on northerly aspects.  Where this layer is present multiple small (D1) skier triggered avalanches with high sensitivity have been reported over the last couple of days.  The depth of storm slabs will vary depending upon proximity to the coast with 8-16 inches in the Maritime zone and less as you move north and east in our forecast zones.

  Assessment of this layer can be tricky as stability will vary depending upon the presence of buried surface hoar.  Where this layer is absent, chances of triggering an avalanche will be much lower as snowfall over the last week has slowly accumulated atop a strong bed surface and there is minimal stress in the upper snowpack.  Areas typically affected by north wind will be unlikely to have the 3/9 BSH layer.

  Use small test slopes that are representative of the steeper terrain you may be planning to travel upon to test the sensitivity of new snow.  Keep in mind the type of avalanche problem you may be dealing with and the mass that it involves.  If traveling in protected north facing terrain avoid exposing yourself to secondary exposure like terrain traps or cliffs where even small avalanches have the potential to have serious consequences.

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  North winds kicked up on the Thompson Pass weather station overnight into the 40s.  Wind slabs have been observed in specific terrain over the last few days with low to moderate sensitivity.  Where wind slabs have been found they are generally around 6 inches deep or less and have been found to exist in small pockets.  Last night's increase in wind along with snowfall from the 12th will allow wind slabs to become a bit deeper and grow in size spatially.

  Keep an eye out for how much soft snow is available for transport in the area you choose to travel.  Identify the predominant wind direction and which aspects would be loaded.  Watch for shooting cracks or collapsing on test slopes that would indicate that human triggered wind slabs are possible on specific terrain.  Keep in mind that even shallow avalanches can be dangerous if triggered in extreme terrain or above terrain traps where debris will pile up deeper.  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Temperatures on almost all weather stations began to rise at midnight last night with sea level temps above freezing as of 6 am.  This increase in temperature will allow for human triggered and natural wet loose activity to occur earlier today than what may be typical.  The extent of this activity will depend on how long the skies stay clear.  Natural wet loose activity was observed yesterday originating from steep rocky solar aspects up to D2 in size.

  Pay attention to not just the terrain you are on but what is above you.  Avoid traveling in steep rocky terrain at low elevations where the surface snow is becoming moist.   Also, avoid travelling below steep rocky faces that are baking in the sun.  The size of potential wet loose slides directly correlates with the vertical relief of a slope and the amount of soft snow that sits on the old late Feb wind board.  It is unlikely at this point for wet loose activity to be able to step down below this old wind damaged snow.