Maritime

Problemi valanghivi

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Likely

  Dimensione

  2–3

  Dangerous avalanche conditions continue to exist.  Human triggered avalanches are likely that could be large enough to injure, bury, or kill a person.  DOT has recorded an estimated 56 inches of snow since 1/4 at road level, with 6 inches in the last 24 hours.  During this time period the freezing line has been dynamic with rain occurring up to 3500' on the 6th.  Since then the rain line has settled around 1000' with Keystone Canyon being the transition zone.  However, mixed precipitation was reported overnight all the way to DOT camp.

  This dynamic freezing line has created storm slabs with varying characteristics depending upon elevation.  

  Below 1500' storm slabs are not a concern as mostly rain has occurred at low elevations.

  Between 1500-3000'- There is a stout rain crust that is in the bottom 1/3rd of nearly 3 feet of settled storm snow.    The snow beneath the rain crust is being insulated by the snow above and remains moist.  Propagation was observed at the interface of new/old snow and below the mid storm rain crust on 1/8.  

  Above 3000'- The 1/6 rain crust gradually disappears, with greater storm slab depths.  The effect of a fluctuating freezing line can be seen in density changes within the storm snow, which can act as failure planes.

  Light snowfall and light wind is expected to continue today before increasing in intensity tonight.  There is a lot of powder to enjoy safely, the key will be paying attention to terrain and keeping slope angles low.  

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Likely

  Dimensione

  1–2

  Rain on snow continues to occur at low elevations of the Maritime snow climate zone.  The entire snowpack is saturated with water at low elevations at this point.  A lot of wet loose natural activity has already occurred.    Human triggered wet loose avalanches will be likely today.  The potential danger of wet loose avalanches is directly correlated with how wet the snow surface is, how much snow is available, and the vertical fall and steepness of the slope in question.  The larger the slope, the more entrainment that can occur.  Terrain traps will significantly increase the consequences of wet loose avalanches as even small slides can pile up deep debris.

  It is recommended to avoid traveling on or below terrain steeper than 30° where the surface of the snow is unfrozen. 

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Likely

  Dimensione

  2–3

  Multiple potential weak layers exist in the mid snowpack.  These weak layers are being put under significant stress by heavy snowfall over the last week.  These layers are of most concern in the mid elevation band, but some may exist at upper elevations as well in isolated areas.  

  First and most concerning is the 12/5-10 rain crust sandwich. This layer consists of 2 rain crusts that are separated by about 4 inches with faceted snow in between.  The upper rain crust has lost most of its strength and propagation in stability tests has been observed multiple times this week failing between the crusts.  This layer exists below 3500' and is on average nearly 3 feet deep in the snowpack.

  Second is a layer of surface hoar that was recently buried on 1/4.  Despite rain on snow, this layer was insulated by dry snow that fell at the beginning of the storm, and has been found intact and reactive in stability tests as recently as 1/8.  The distribution of this layer is less continuous than the rain crust sandwich as an uptick in north wind prior to the storm destroyed this layer in many locations above brush line.  This layer continues to exist below brush line and in isolated wind-protected alpine areas.

  Digging snowpits is the best way to identify persistent weak layers, and ECT and PST tests are the best way to evaluate their sensitivity.