Continental

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  The forecast remains largely unchanged from yesterday.  Wind slabs that were created by the outflow event at the beginning of February, have been observed to show signs of instability in small pockets in isolated places.  Wind slabs were deposited on top of a 3 foot deep upside down storm slab from 1/28-29.  The poor structure near the top of this storm snow is what has made these wind slabs persistent.  Where instabilities have been noted failure is occurring ~ 4 inches below wind slabs where a density change exists.  

  This instability has been noted where wind slabs are thinner (1 foot or less) and smaller in size spatially.  The larger and thicker wind slabs have been set up more thoroughly and are unlikely to be affected by a person or machine due to their strength.  If one of these larger wind slabs were to be triggered it would likely occur near the periphery where the slab is thinner and produce a destructive hard slab.  

  The last couple of days of benign weather has allowed the sensitivity and likelihood of this avalanche problem to slowly decrease.  The 1/28 storm snow is settling, this process has been slow as temperatures have been very cold up until yesterday.  The settling process is making the drier snow near the bottom of the slab more dense and the heavier snow at the top is losing moisture and becoming drier.  The result has been slowly improving structure within storm snow that will lower the likelihood of persistent wind slabs.

  4 to 10 inches of new snow has covered these old wind slabs making them difficult to visually identify.  Pay attention to signs of instability such as shooting cracks or collapsing that would indicate this problem still exists in the area you are traveling.  

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–1.5

  Small wet loose activity is beginning to occur at low elevations on southerly aspects.  Coastal locations will have the greatest effect initially as temperatures are the warmest.    On the north side of Thompson Pass on 2/7 the sun's energy was able to warm the top couple inches of snow, and roller balls began to occur on slopes steeper than 35° originating from bushes or rocks.  These were shallow although could pose a hazard if traveling in steep exposed/ consequential terrain or above terrain traps like creek bottoms.

  The weather forecast is calling for one more day of clear and calm before clouds and precipitation move in.  Small to moderate wet loose activity is expected today on southerly aspects at low elevation.

• 

  Glide Cracks

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  2.5–3

  Glide cracks exist in a few places in all three of our forecast zones.  Town Mountain and Mile High hold the highest concentration of these.  A few glide cracks have released over the last month creating large destructive avalanches.

  The sensitivity of Glide avalanches is not possible to predict.  These release independent of snowpack stability.  Instead of being affected by changes in the surface snow (loading, warming, etc) like all other avalanche problems, glide avalanches are tied to a more complicated relationship between the underside of the snowpack and the friction at the ground.  This interaction is not well understood.  What is well understood is that this avalanche problem produces deadly avalanches that include the entire snowpack and can release spontaneously.

  Travel advice is very simple: avoid spending time under glide cracks.  Glide cracks are generally easy to identify as they look like crevasses, but exist in non-glaciated terrain.  New snow and wind will make identifying these more difficult, as they may have been covered.