Sawtooth & Western Smoky Mtns

Problèmes avalancheux

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Likely

  Taille

  1–2

  Overnight, 4-6" of new snow fell, accompanied by strong, gusty winds. Winds were recorded even at weather stations that are generally sheltered from the wind. This wind is moving both the new snow that fell overnight and the snow that fell over the past week (view storm totals here). Thanks to the strong winds, expect to find slabs in middle and upper elevation terrain, both near ridgelines and adjacent to mid-slope features like ribs and gullies. 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.

  Today's wind slabs will be plenty dangerous on their own, but you're also more likely to trigger a persistent slab avalanche (Problem #2 below) on wind-loaded slopes. You can greatly reduce your risk of triggering an avalanche of any variety by sticking to slopes that are sheltered from the wind.

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Possible

  Taille

  2–3

  Layers of weak snow can be found near the ground and in the upper half of the snowpack:

  1. In the upper 2-4' of the snowpack are several interfaces that have produced avalanches and unstable test results in recent days. 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 to be destined to talk about for the remainder of the season. This layer is buried 4-6' deep in this zone, making it much more difficult (but not impossible) to trigger.

  On Friday, Chris and I visited the scene of a very large avalanche in Smiley Creek that was triggered by a snowmobiler. Unfortunately, the man was caught and killed in the avalanche (photo at right/above, more details here). This avalanche failed on a crust/facet layer buried underneath a 3' thick slab of snow. Saturday, we went to Beaver Creek to look for this layer. We found it. It took some force, but it failed cleanly during snowpack tests. We also saw a natural avalanche that likely broke on this layer. Sunday, a skier in the Alturas Creek drainage experienced a very loud collapse that likely involved this layer, and yesterday an observer reported a recent, large natural avalanche that failed on a southeast-facing slope in alpine terrain in the Sawtooths. Continuing snowfall and wind-loading are keeping these weak layers reactive.

  Given the uncertainty surrounding these weak layers, skiing or riding in "prime-time" avalanche terrain is a risky business. 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. While triggering a wind slab (Problem #1 above) is more likely, a wind slab avalanche could easily step down into these persistent weak layers, resulting in a much larger avalanche.