Continental

Avalanche problems

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2.5

  After multiple rounds of heavy snowfall skies will finally clear today.  Over the last week we received a storm on the 13-14th that deposited 12-18 inches on Thompson Pass.  Clear weather on the 15th saw numerous human triggered avalanches as users immedietly began to travel in steep terrain.  The 16th-18th saw an additional 18-24+ inches above 3000 feet that was more dense than the previous storm.  It is unknown at this point how well the new heavier load of snow will bond with the drier snow beneath, but the top heavy setup is not ideal.  The new snow will need time to settle and bond with the underlying layers.  

  Today, expect for the new snow to be reactive to human triggers in steep terrain.  We are expected to see some sun today, which helps the snowpack to settle in the medium-long term.  In the short term the sun will be increasing the avalanche hazard through the day as the surface snow heats up and becomes more dense (slabby).  We have not seen the sun much this April.  Instead, snowfall has slowly been accumulating since the 4th and became heavy over the last week with two major storms described above.  The sun will be a major change for the upper snowpack as the strong mid April sun comes out.   Major changes create stress in the snowpack, as that stress builds human triggered avalanches become more likely.

  Storm slab and wet loose(see problem 3) are the most likely problems to encounter today.  The most dangerous problem is deep persistent slab concern (see problem 2).  storm slab avalanches have the potential to step down to a weak layer in the snowpack that is buried 3-6 feet deep creating very large avalanches.

   

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  2.5–3

  A weak layer of snow that formed during the extended sunny weather in March is at the breaking point.  This layer does not exist everywhere but has been found above 4000 feet on shaded aspects.  Terrain that is commonly wind-protected will be areas where this layer is most likely to persist.  Where this layer exists VERY DANGEROUS AVALANCHE CONDITIONS EXIST.    Slopes that have this weak layer could be triggered by a skier or snowmachiner and produce avalanches 3-6 plus feet in depth.

  Our last clear day of clear weather on Tuesday 4/15, saw avalanches triggered at this layer by snowmachines, skiers, hikers, and helicopters.  Multiple close calls were reported, including this report from Billy Mitchell (see  avalanche observation here), which we are grateful this person was humble enough to report and document well so others can avoid triggering one of these deep slabs.

  An additional 2 feet of snow since the 15th has further increased the stress on this weak layer.  Users could be lulled into complacency as they see tracks from other users that do not trigger an avalanche.  Tracks are not a sign of stability with this avalanche problem.   A slope could fail after multiple tracks have been laid down.  

  On 4/15 the upper snowpack showed  good structure and strength despite a dangerous weak layer being in place.  The structure of the upper snowpack and the depth of this layer will make assessment misleading and challenging for novice and professional users.  

  It is strongly encouraged to keep terrain choices moderate and simple.  If a person were to trigger one of these avalanches today, it would very likely be an unsurvivable event.

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Very Likely

  Size

  1–2

  Even though Wet loose is listed as the third avalanche problem, it will pose a significant hazard today in specific areas.  There is a lot of new snow that has accumulated over the last week.  This new snow has not yet seen much sun to allow it to settle.  Expect for the new snow to rapidly destabilize as the sun comes out today.  The first aspects to  be affected will be East moving around to South and then finally West.  Slopes that are perpindicular to the sun will be the most prone to natural and human triggered wet loose activity.  Steep rocky areas will be the first to be affected  as the suns energy is more efficiently absorbed by the dark color of rocks and then transmitted into the surrounding snow.  The solar facing rocky terrain that hangs above a lot of our steep ramp terrain will be active during the heat of the day.   Wet loose avalanches may be able to create enough force to step down to deeper layers in the snowpack.

  Low elevations are expected to become isothermal on all aspects.  Avoid travel in steep terrain at low elevations and slopes that are heating up.  Pay attention to the terrain above you as well as the terrain that you are travelling through.