Hatcher Pass

Avalanche problems

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3

  This problem is a double-edged sword. The deeper the weak layers, the harder it will be to trigger an avalanche but if you do trigger an avalanche the consequences will be huge.

  After last week's significant storm on Jan 22-27th that deposited more than 56" of new snow with 11" of SWE at 3550' and 38" of new snow with 7" of SWE at 2700' the snowpack has changed in many ways.  Strong wind, rain below 3000', and warm temperatures throughout the forecast area created havoc in the snowpack, building new slabs and stressing old weak layers, which resulted in a widespread natural avalanche cycle. Since the storm, temperatures took a dramatic dip into sub-zero and single digits.  We expect this recent freeze to have stabilized short-lived instabilities like wind slabs and storm slabs.  However, we still expect to see poor structure and the potential for propagation on deeper, weaker layers that formed early season. These will be hard to find and trigger because of the depth of the weak layer. Riding a snowmachine will have more force and affect deeper weak layers, increasing the potential for triggering an avalanche. 

  Although trending more unlikely, it remains possible to trigger a deep persistent slab 3-6' in depth on leeward aspects and locations with a deeper snowpack. Human triggering or remotely triggering a large slab will be possible on 30 degree and steeper terrain at mid and upper elevations where hard slabs are sitting over weak, sugary facets. With cold clear calm conditions the latter half of this week and forecasted for several more days, expect this problem to linger and become more stubborn and harder to trigger. 

  Remember that deep persistent slabs (DPS) are unpredictable and often give infrequent feedback. Human triggering can happen days or weeks after a storm. These avalanches can be remotely triggered in isolated locations from flat terrain and have unusually wide propagation.

  PERSISTENT SLABS:  At low elevation and on shallower windward aspects, less snow depth exists. Expect it to be possible to trigger persistent slab avalanches 1-3' deep in terrain 30 degrees and steeper in these locations. 

  Due to the road closure, we have not gathered a lot of information above 3000'.  Our confidence remains moderate with this avalanche problem. Considering the potential high consequences of this avalanche problem, we recommend a conservative approach to terrain management.

  When the avalanche problems are complex and some uncertainty exists, it’s time to focus on safe travel protocol. In avalanche terrain, only expose one person to steep slopes at a time, choose safe zones out of the reach of avalanches for grouping up and expect avalanches to run further than you think, always have a spotter in a safe location, everyone carries a beacon, shovel, and probe, and are prepared and practiced for companion rescue.

  ****For more photos from the recent avalanche cycle, check out this observation and video.