Sawtooth & Western Smoky Mtns

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  2–3

  Yesterday, Chris observed two large avalanches in the vicinity of McGown Peak (observation). Monday, an observer reported a recent, large natural avalanche that failed on a SE-facing slope in alpine terrain in the Sawtooths.  Strong winds in the past couple of days moved snow onto many slopes, stressing the weak layers near the ground and in the upper half of the snowpack:

  1. In the upper 2-4 feet of the snowpack, multiple interfaces have produced avalanches and unstable test results recently. In this zone, these layers appear to be worst on slopes that face the sun, where they are accompanied by a crust (photo, video). 
  2. Depth hoar exists near the ground on all aspects. This is the snow that we've been talking about all season long and seem destined to talk about for the remainder of the season. This layer is buried 4-6 feet deep, making it much more difficult (but not impossible) to trigger.

  Given the uncertainty surrounding these weak layers, skiing or riding in "prime-time" avalanche terrain remains risky. You are more likely to trigger an avalanche on wind-affected slopes steeper than about 35 degrees, but these weak layers exist in sheltered terrain as well.

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  In the past two days, professionals near Copper Mtn reported that small wind features were reactive to ski cuts, and they avoided very steep avalanche paths and all wind-loaded starting zones. Professionals in the mountains near Smiley Creek reported extensive wind-loading in exposed upper and middle elevation terrain. Some wind slabs may have been deposited above temperature or rain crusts that formed Monday.

  Expect to find wind slabs near ridges, on the sides of cross-loaded gullies, and lower on slopes near prominent terrain features. Owing to the near-vertical nature of the Sawtooths, the wind also tends to blow snow down cliff faces where it accumulates in spindrift slabs on the aprons below. Continued light snowfall may mask some of the obvious signs that the wind has been at work, but it's a safe bet to assume upper elevation slopes and many middle elevation slopes have been wind-loaded in the past two days. 

  Recognize that the recent wind event also added stress to the weak layers buried deeper in the snowpack (described in Problem 1 above). Any wind slab you trigger could step down to these deeper layers, producing a much larger, more dangerous avalanche.  You can greatly reduce your risk of triggering an avalanche of any variety by sticking to slopes that are sheltered from the wind.