Mt Hood

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1.5–2.5

  While the snow will taper off Tuesday night, strong to extreme westerly winds will linger into Wednesday morning.  

  With winds relentlessly loading the same avalanche paths on the upper mountain, thicker slabs will have formed above treeline, increasing the chances for large and destructive avalanches that can run long distances.  Wednesday is not the day to try to nuance terrain selection around large avalanche paths.  

  At mid and upper elevations, avoid steep open slopes steeper than 35 degrees. Wind slabs may have formed further downslope than usual.  If you're traveling above treeline, stick to scoured ridges and leave a wide buffer between you and avalanche runouts. Make sure to give cornices a large buffer as they may break back further than you expect.  Blowing snow may reduce visibility, especially in the morning. 

  To travel safely below treeline Wednesday, you'll need to think about avoiding wind slabs not just in the usual areas below ridgelines but on open slopes below treeline.  While you're likely to find wind-stiffened snow in many areas, if you see shooting cracks or evidence of recent avalanches, these are clear signs to choose lower angled terrain. It's possible that new winds slabs have built over weak snow buried 12/18.  In these areas, avalanches will be easier to trigger and may break further across the slope than normal.  

  

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  1–2

  Our persistent weak layer will have received a good test Tuesday and Tuesday night, with heavy dense wind-driven snow at the same elevations we've been tracking this problem.  With few direct observations during the storm on Tuesday, we don't know if avalanches released on this layer or if it's become more or less likely to trigger a persistent slab avalanche.  Step out with caution after this storm, especially in areas where we think this avalanche problem lingers. 

  Prior to this system, observers were continuing to find this weak layer in test pits. As recently as Monday, one observer reported an isolated whumph on Vista ridge.  The persisent weak layer of interest (12/8 buried surface hoar) can be found in the upper 2' of the snowpack.  You can locate this layer by using snowpack tests and looking for a thin gray in the upper snowpack.  Since its burial, we have been tracking its distribution across the terrain closely.  Most sightings of this layer been below and near treeline, specifically on open slopes with minimal canopy.  

  It's been over a week since our last known avalanche on this layer.  As of Sunday (12/18), NWAC staff were easily able to still locate this thin gray line of surface hoar in the Vista Ridge area.  The good news is we noticed this surface hoar rounding and becoming harder and harder to fail in snowpack tests.  The bad news is we’re still receiving propagating test results when it does fail.