Continental

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  2–3

  Skies are forecasted to be clearing today along with an increase in north wind.  Thompson Pass weather station showed north winds increasing immediately after a wind direction change from south to north.

  There is significant dry snow available for transport.  Dangerous avalanche conditions are expected today as north winds build fresh wind slabs up to five+ feet in depth.  Storm snow was already found to be upside down with signs of instability present on Thompson Pass.  Wind loading will make lee sides of ridges and terrain features more top heavy and sensitive to human and machine triggers.  Cross loaded terrain will be especially dangerous today.

  Pay attention to wind direction and avoid areas that are being actively loaded.  Hard snow over soft will indicate wind loaded snow and shooting cracks are a bullseye indicator of instability.  Wind chill is going to be a serious concern as well over the next couple of days with temperatures currently plummeting and winds ramping.

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1.5–2.5

  Instabilities still exist in areas that are protected from north wind today.  The 1/28 snowstorm delivered 3+ feet of new snow from the coast to 46 mile.  Thompson Pass probably received the highest amounts.  Exact snow totals are unclear, but 40 inches of settled storm snow was observed on 1/30 at Thompson Pass.    This new snow fell on a variety of wind damaged surfaces.  

  The significant amount of snow we just received will need time to bond to old wind affect.  Bonding is beginning to occur at this interface, although some sensitivity was still observed on 1/30.  In addition to the new/old interface, storm snow is upside down and  instability was found within storm snow down 1 and 2 feet.  The 1/28 storm slab will likely need more time to settle than what is typical.

  Hand shear tests are nearly impossible to perform due to the depth of new snow.  Be careful using test slopes as failure on even small slopes could be dangerous due to the mass involved.  Extended column tests and propagation saw tests are probably the best way to assess upper snowpack stability.  Although these can provide false stable results.

• 

  Glide Cracks

  • All elevations

  Likelihood

  Unlikely

  Size

  2.5–3

  The sensitivity of Glide avalanches is not possible to predict.  These release independent of snowpack stability and are tied more to a 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.