Continental

Avalanche problems

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Shallow storm slabs are expected to develop today.  Coastal mountains are expected to see the highest amounts of precipitation with 10 inches of new snow possible at upper elevations before the current storm dissipates.  The northern end of our forecast area is only expecting a trace of snowfall with Thompson Pass falling somewhere in between.  Southerly winds this morning are moderate at upper elevations and are forecasted to decrease through the day.

  The presence of surface instabilities today will depend upon new snowfall amounts and the effect of moderate southerly winds have on redistribution.  The most likely places to trigger an avalanche today will be areas that receive more than 6 inches of snow and where wind has created deeper stiffer storm slabs.  

  New snow will add a slight amount of stress to faceted snow near the surface.  The effect of this is expected to be minimal with this storm.  Areas near that coast that  receive higher snowfall totals are also those where buried near surface facets are less significant.  Whereas the continental zone, where faceting is more significant beneath the surface snowfall amounts are not expected to amount to more than a couple of inches.

   

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  1–2

  Faceted snow exists near the surface in all three forecast zones that was created by the mostly dry and cold weather since Christmas.  As is typical, facet development is more significant as you move away from the coast.  

  In many places near surface facets have been buried by wind slabs formed by north winds.  This north wind has disrupted the distribution of facets in wind exposed areas with windward slopes being wiped clean and lee slopes forming wind slabs over facets.  Protected areas will have a more continous distribution of faceted snow.  If this sounds complicated,  its because it is.  A significant amount of spatial variability now exists in our forecast area with persistent wind slab concerns existing in some places and stable snow existing in others, often in close proximity.

  There is a moderate degree of uncertainty with the sensitivity of persistent slabs currently.  Although, an observation from 1/13 of shooting cracks through old very hard wind slabs at Cracked Ice yesterday indicates faceted snow still has the propagation energy required to create avalanches in some locations.

  The current storm is not forecasted to produce the amount of snowfall that would be required to overload faceted snow beneath the surface and make human triggered avalanches likely.  This avalanche problem is difficult to assess.  It is reccomended to perform snowpack stability assesment on more of a slope by slope basis moving forward.

  

• 

  Glide Cracks

  • All elevations

  Likelihood

  Unlikely

  Size

  2.5–3

   Glide avalanches are a strange beast that act differntly than other avalanche problems.  Full depth failure can occur independent of snowpack stability.  Or in other words, they can release even when a stable snowpack is in place.

  Since it is not possible to time their sensitivity the only way to mitigate this hazard is by avoidance.  First identify where glide cracks exist and avoid spending time beneath them.  Glide cracks are easy to identify.  They look like crevasses, but exist in non glaciated terrain.

  These do not produce small avalanches,  but rather failure will include the entire snowpack.