Sawtooth & Western Smoky Mtns

Lawinenprobleme

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  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  2–3

  Wednesday, 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.  Today's storm will build wind slabs on many slopes, stressing weak layers throughout the snowpack:

  • Periods of sun, warm temperatures, and rain created a variable mix of crusts and facets near the snow surface. These crust + facet layers along with small facets beneath the current storm snow may produce smaller but touchy slab avalanches as snow accumulates.  
  • 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). 
  • 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

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Very Likely

  Größe

  1–2

  The Sawtooths and western Smokys will pick up 8-12" of new snow by 5 PM, adding to last night's 2-6". This storm is producing low-density snowfall of about 4-5%.  Wind will blow moderate to strong from the west, and it won't take much wind to get this snow moving. Expect whiteout conditions at upper elevations and any middle elevation terrain exposed to the wind. 

  Yesterday professionals on Copper Mtn (near Banner Summit) found that thin fresh wind deposits and cornices were sensitive to their weight. Expect these drifts to grow in size and extent today. Wind slabs are most commonly found near exposed ridgelines, 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. Some slabs may sit atop temperature or rain crusts that formed Monday; making them particularly touchy.

  Recognize that active wind-loading also adds 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.