Avalanche forecast

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 7 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Avoid wind-loaded slopes to reduce the chances of triggering large avalanches. You could trigger slides involving just the fresher drifts or very large, destructive avalanches that fail on weak layers deep in the snowpack. Sheltered slopes are less likely to slide, but do not assume they are safe. 

Possible heavy snowfall and strong winds tonight could cause the avalanche danger to spike. If you are out after dark when the next storm hits, stay off of and out from beneath steep slopes. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Expect to find multiple generations of soft and stiff wind slabs in exposed terrain. While most of the drifts have had several hours to stabilize, you will be able to trigger some of them. The size and extent of the wind slabs increase as you move up in elevation; in alpine terrain, I would expect to find 2-5 foot thick drifts.

    Winds shift more southerly and could increase this afternoon, possibly producing a new crop of wind slabs. Ben's video from a couple of days ago (click here) drives home how quickly wind can move large amounts of snow. 

    Look for smooth pillows, dunes, and wave-like features on the snow surface to identify wind-loaded areas. If you feel the snow become stiffer as you travel or see cracks shooting out from your sled or board(s), pay close attention to slope angles. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Huge, destructive avalanches remain possible as the weak layers in the snowpack adjust to the load from the multi-day storm.  Yesterday, Ben saw a monster avalanche in the mountains northwest of Stanley (video). The slide was 3-10 feet deep and almost a half-mile wide, failing in shady upper elevation terrain.  An observer reported a large avalanche put 6-10 feet of debris on the Beaver Creek road (photo). Monday, Ben found an avalanche in the White Clouds that failed on weak snow near the ground (photo at right, video here). It broke hundreds of feet wide in a heavily wind-loaded area when a large cornice collapsed and hit the slope. 

    The weak layers in the middle and bottom of the snowpack are widespread but are most sensitive to triggering where winds have added extra weight to a slope.  However, there's a chance you could trigger one of these beasts in sheltered terrain. The deeper persistent slab avalanches are difficult to trigger because the weak layers are so far below the surface, but the consequences of getting caught are severe.

    Avalanches failing on persistent weak layers can break wider than you expect, spanning terrain features and changes in aspect. These slides may be triggered remotely — from gentle terrain above, beneath, or to the sides of steeper slopes.

Avalanche Discussion

The feet of recent low-density snowfall is making it difficult to evaluate hazard on individual slopes. A few trends and points worth highlighting:

  • Elevation: Snowfall and wind-effects increase as you gain elevation. Persistent weak layers in the lower part of the snowpack are more prevalent at upper elevations than in many seasons. This makes avalanches both larger and more likely as you climb.
  • Deep slabs: Visibility has been almost non-existent, but we've seen or received reports of at least 3 avalanches that broke over a meter deep, including one crown up to 10 feet tall. In the Sawtooths, western Smokys, and Banner Summit area, we're transitioning to a deep persistent slab problem. This is a classic "low probability + high consequence" scenario. 
  • Snowpack complexity: Weak layers in the lower and middle portions of the snowpack are notably variable in appearance, strength, and distribution. SAC staff and other local professionals are struggling to keep track of exactly which weak layers exist over large areas let alone on individual slopes. 

What's the take-home point from all of this? Assume all avalanche terrain is "guilty" until proven innocent. Prove to yourself — beyond a reasonable doubt — that a given steep slope is stable before skiing or riding it. 

Regions covered