Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Sat
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Very dangerous avalanche conditions exist. Human-triggered avalanches large enough to bury people are likely to occur. These slides are likely on all steep slopes but will be larger and more dangerous as you climb into terrain that's been exposed to the wind. Yesterday, multiple large avalanches were triggered from gentle terrain hundreds of feet away from the slope that slid. Expect the same again today.

Avalanche problems

  • Persistent Slabs

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

    Triggering a large to very large 1-4 foot thick Persistent Slab avalanche is likely on both sheltered and wind-loaded slopes. The size of these slides will increase as you climb into areas that are affected by the wind. Many natural and human-triggered avalanches were reported yesterday. Most of these involved the two prominent weak layers described below:

    1. Over the last two weeks, storms built a hefty slab that rests atop a mix of crusts, facets, and surface hoar. This weak snow layer exists on all upper and middle elevation slopes and on shadier, lower elevation aspects. 
    2. An older and deeper layer of weak snow exists on all upper and most shaded middle-elevation slopes (W-N-E). Any triggered avalanche has the potential to "step down" to this weak snow near the ground, producing a huge and unsurvivable avalanche.

    Many slopes are primed and ready to be triggered. Consider your proximity to overhead hazards. These slides can be triggered from a distance, including flat terrain near the base of steep slopes. 

    (1/15/2024) This large avalanche broke over 2,000' wide on E-SE-S facing slopes around 8,500' on the south end of Copper Mtn. It failed on a weak snow layer that developed during the long drought in December.

  • Wind Slabs

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

    While the Persistent Slabs described above are by far the biggest concern, human-triggered Wind Slab avalanches big enough to bury people are likely. These slides and relatively small loose snow sluffs can trigger the much larger Persistent Slabs described above. 

Avalanche Discussion

By all accounts, yesterday was a spooky day in the mountains, and today will be much the same. 

Highway 75 at Galena Summit was blocked by a natural, Persistent Slab avalanche (photo). Sledders in the western Smokys triggered a huge Persistent Slab avalanche from a safe location hundreds of feet away (photos). Scott remote triggered three avalanches in Baker Ck (photos, videos) and Brooke described booming collapses in the Northern Sawtooths that sounded like "a muffled cannon." A local guide summed it up well: "One of those days where you pulled out the inclinometer and measured the slope not just once, twice, but maybe three times to confirm that you weren't in avalanche terrain." 

Today's mild temperatures will continue to consolidate the hefty slab built during the storms of the last two weeks. This slab thickens as you climb due to higher snow totals and wind and rests atop multiple fragile, buried weak layers. Signs of instability are everywhere. Observers report collapses that travel thousands of feet before finding a steep slope to release a slide. Recent avalanches have pulled back into low-angle terrain near ridgetop, making safe mountain travel difficult. 

Triggering an avalanche is likely today on all steep slopes. As you head into the mountains, recognize that avalanches can be triggered from flat terrain a long distance from the slope. This means they may break well above you while descending or at the bottom of a slope. Enjoy the fresh snow, but widen those safety margins. Re-think your "safe" routes. Ask yourself, how far will that path run? How close am I to the edge?

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