Continental

Avalanche problems

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Temperatures have been on the increase, moving towards more seasonal norms as a weak low is bringing light to moderate snowfall to all three forecast zones.  As of 6 am Valdez had received 4 inches of new snow with upper Tsaina valley snotel showing similar amounts.  An additional 2-6 inches is forecasted today along with moderate winds out of the E-NE.  Wind direction will likely vary depending upon terrain influence today.

  New snow will be low density and is once again falling on a variety of surfaces ranging from various wind affected snow, exposed rain crusts, and protected powder that has undergone some faceting during the recent cold weather.  The dry snow we are receiving today is not expected to form widespread slabs.  Cohesive storm slabs may form where wind redistribution creates deeper and more cohesive (stiff) pockets of storm snow.  Human triggered avalanches are possible in wind loaded areas up to 1 foot in depth.

  Pay attention to new snowfall amounts and the direction the wind is blowing in the area you choose to travel.  Use test slopes to determine the sensitivity of new snow especially where wind has created deeper pockets.  Watch for signs of instability including: shooting cracks, collapsing, and avalanche activity.  If any of these are present stick to more moderate terrain to lower your exposure.

  New snow will mask old wind slabs, making them more difficult to identify.  Old wind slabs have been reported to show signs of instability as recently as 1/3 (see problem 2)

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1.5–2.5

  Wind slabs that began to form on 1/31 with moderate outflows have gained strength and are stubborn to unreactive to triggers in most locations.  In isolated places, instability has been observed and reported as recently as 2/3.  It remains possible to trigger pockets of old wind slabs ~ 1 foot in depth in isolated locations.  

  On the south side of the pass, wind slabs overlie a rain crust up to 1700', although this number has been found to vary significantly from place to place.  Above rain line wind slabs were deposited on a deep top heavy storm slab.  A density change near the top of this storm slab is likely why instabilities continue to exist above the rain line.  Below the rain line, the 1/29 rain crust is beginning to break down and may be acting as a weak layer as well.

  In areas where wind slabs continue to show instability, they have existed in small pockets and around 1 foot in depth.  Larger more extensive areas of wind slab have been observed to be locked up and unreactive.  Yesterday these pockets of wind slab were easy to visually identify as they have a rounded smooth appearance.  Today, new snow will hide this distinction making these areas much more difficult to detect and avoid.

  

• 

  Glide Cracks

  • All elevations

  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.