Continental

Avalanche problems

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Light to moderate snowfall has started to fall across the entire forecast area.  3 inches have accumulated at the Sugarloaf Snotel and a trace at 46 mile as of 6am.  The report from Thompson Pass was not available.  Snowfall totals are expected to add up to 6-8 inches in the Maritime upper elevations with lower amounts on Thompson Pass.  Only light winds are expected to accompany this new snow so shallow storm slabs are not expected to be a major hazard today.  

  New snow is acccumulating atop old powder, surface hoar in some areas at low and mid elevations and old wind slabs formed on 3/7 and 3/10.  The most sensitive areas will be where surface hoar exists as this has the potential to become a weak layer in our snowpack in the future once more snow accumulates.  Old wind slabs have mostly locked up and gained strength, but may remain possible to trigger in isolated areas.

  Pay attention to new snowfall amounts and the amount of associated wind redistribution.  Use hand shear tests and test slopes to gauge how well new snow is bonding to older surfaces.

  The hazard will be higher if snowfall amounts are higher than forecasted.

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1.5–2

   

  There are currently 2 persistent weak layers on our radar, both are believed to be limited to terrain below 3000' and are not widespread issues even in the elevation band where they exist   There is a layer of buried surface hoar from Valentine's Day as well as weak snow below a decomposing rain crust from late January.  Additional snow and wind loading are slowly adding stress to these layers where they exist.

   Buried surface hoar from 2/14 exists in previously wind-protected areas from 1500 -2500 feet.  This layer is difficult to identify as it has only been found in a narrow elevation band and exists in terrain that was protected from the strong outflow (North) wind event that occurred in late January.  This layer has been found on average between 12-20 inches in depth.  This layer has been observed to be well defined in isolated areas.   Propagation in ECT tests has been observed in one location as recently as 3/6.  

  Below 1500 feet, a rain crust is buried 16-20 inches and has shown propagation beneath the crust in snow pits as recently as 3/5.  Due to the low elevation, this is only a concern in a limited amount of terrain.  This layer could be a concern in steep low elevation canyons, or on steep unsupported slopes below 1500'.  Use caution when traveling through low elevations with poor snowpack structure. 

   To limit exposure to both of these layers avoid terrain traps and consider using conservative terrain while moving through low elevations..  There is uncertainty about the current and future reactivity of these two layers.  There have not yet been any observed or reported avalanches on either of these layers.  We are keeping these on our list, as current weather conditions will continue to stress these layers.