Maritime

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1.5–2.5

  Our extended period of calm winds will come to an end as North winds are forecasted to increase today with gusts to 50 mph in response to an approaching front.  This increase in wind is expected to be brief as the approaching front moves onshore tonight, limiting the duration of this wind event to the daylight hours today.  Despite the short duration, the avalanche hazard is expected to increase with the onset of winds as there is an abundant amount of snow available for transport, especially in the Maritime snow climate zone.  Expect to encounter windslabs on the lee side of terrain features, cross loaded gullies and high elevation ridges 1-2 feet in depth that are reactive to human and machine triggers. Watch for signs of wind slab formation such as: active snow transport, fresh wind lips and stiffer snow at the surface.  Shooting cracks and collapsing are direct indicators that wind slabs have the potential to produce an avalanche on slopes steeper than 30°.

  In areas that are not being affected by wind there is also a storm slab concern at this point.  Incremental snowfall since 2/14 has now reached the point where instabilities within various pulses of snowfall are now a concern.  Good bonding continues to be observed at the 2/14 wind affected layer that exists above 3000'.  However, lower elevations are harboring buried surface hoar that is now under a sufficient slab to be an issue between 1500-2500' and poor structure exists below 1500' in the top meter of the snowpack (see problem 2)

  Low elevation terrain is expected to see less of a wind slab issue as winds will likely be lighter and warm temps have created denser snow that will be more resistant to redistribution.

   

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1.5–2

  There are 2 persistent weak layers of current concern.  The first is the Valentine's buried surface hoar.  This layer only exists in a narrow elevation band ~1500-2500' and is now sufficiently buried to be an issue in steep terrain that falls within this elevation band.  Even within this band, the distribution of this layer is spotty, which will make assessment challenging.  This BSH layer has been identified as recently as 2/25 in the Port of Valdez at 2500', down 20 inches.  Slabs overlying this weak layer are closer to 12-16 inches deep on Thompson Pass.  We have not yet seen this layer produce any avalanche activity, but with continued incremental loading of snowfall forecasted in the future, it will be important to remember this layer when traveling between 1500-2500'.  Choosing conservative routes through this elevation band will be the best way to avoid this problem, as the threshold strength of this layer is unclear.  Wind loading on this layer is a concern. However, the formation of this grain was most pronounced in wind protected areas, making it less likely for wind loading to occur in areas where BSH is the most pronounced since this wind event is expected to be short and relatively mild.

  The second persistent weak layer of concern is faceted snow that exists below a decomposing rain crust from late January down 12-16 inches in the snowpack.  This poor structure exists below 1500' and was producing large collapses across connected terrain as recently as 2/25 in the Maritime zone with moderate ECT scores producing propagation in multiple locations over the last week.  Same with the Valentines BSH this layer exists in a specific elevation band.  Steep low elevation canyons are the most likely areas to see this layer be reactive.  Continued snowfall this week will put additional stress on this weak layer.  Natural avalanche activity will become possible if we receive a heavy load of new snowfall later this week.  Once again the best travel advice is to recognize where this layer exists and choose conservative terrain to move through.

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  A fresh round of new snow has fallen over the last couple of days that will quickly react to solar input if the sun is able to break through the clouds as predicted.  This period of wet loose is expected to be short lived today as a front will push clouds and additional precipitation on shore this evening.

  When assessing wet loose hazards, it is essential to take the hazard in relation to the terrain you are exposing yourself to.  Are there terrain traps? Are there consequences if I were to be swept off my feet by even a small avalanche? 

  The size and shape of the terrain above you along with the amount of loose snow available to slide, directly correlates to the size of the wet loose activity that can occur. Terrain traps and exposure below you compound consequences.