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

  Two large, natural avalanches released yesterday or Monday night in wind-loaded, south-facing terrain just north of Galena Lodge (view observation). 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. 
  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 here, making it much more difficult (but not impossible) to trigger.

  On Friday, Ben and Chris visited the site of an avalanche fatality in Smiley Creek (photo to right/below, details here). This avalanche failed on a crust + facet layer buried underneath a dense, 3-foot thick slab. In Beaver Creek, the same layer failed cleanly during snowpack tests and likely produced a recent natural avalanche. Sunday, a skier in the Alturas Creek drainage experienced a very loud collapse, and an observer reported a recent, large natural avalanche that failed on a southeast-facing slope in alpine terrain in the Sawtooths on Monday. 

  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. I'm especially leery of SW-S-SE facing avalanche paths where we have the "double whammy" of a crust+facet layer about 3 feet down and recent wind-loading; think long and hard before skiing or riding those slopes.

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Expect to find wind slabs near ridgelines and lower on slopes in exposed terrain. Tuesday near Copper Mtn, professionals reported that small wind features were reactive to ski cuts, and they avoided very steep avalanche paths and all wind-loaded starting zones. Also Tuesday, professionals in the mountains near Smiley Creek reported extensive wind-loading in exposed upper and middle elevation terrain. 

  You could find the recently formed wind slabs near ridges, on the sides of cross-loaded gullies, and lower on slopes near prominent terrain features. Watch for dunes, scallops, and textured snow surfaces. While these features may not produce shooting cracks like classic drifts and slabs, they are clear signs the wind has transported snow. 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. Wind slabs should be most sensitive to triggering on slopes over about 35*.  

  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.