Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 4 years ago.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

Highlights

Dangerous avalanche conditions exist. Avalanches failing in the new snow are likely and will be large enough to bury you. Much larger avalanches failing on weak snow buried 3 to 4 feet down may run down into low elevation terrain and will be unsurvivable. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes.

Avalanche problems

  • Persistent Slabs

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

    A layer of weak snow is buried 3 to 4 feet beneath the snow surface. This layer has produced countless large avalanches in the past two weeks. 18-24" of snow fell in the past 4 days, adding significant stress to this weak layer. Human-triggered avalanches failing on this weak snow are likely. These slides will be very large, and likely unsurvivable. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes. Sluffing, cornice breaks, and wind and storm slabs can act as very effective triggers for deeper weak layers, "stepping down" to release a very large and dangerous slide.

    (12/11/2022) This large avalanche occurred just outside of the ski area boundary on Bald Mountain. The human pictured is 6 feet tall. The crown was 3-4 feet thick. It failed on the layer of weak, faceted snow that is widespread in our forecast area. This slope faces NW at 8,800'.

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5

    18-24" of snow fell in this zone in the past 4 days. Moderate to strong winds have blown from a variety of directions and have built thick slabs in exposed terrain. These slabs will be reactive to your weight today. In sheltered terrain, enough snow has fallen that slabs failing on surface hoar and weak facets are possible, and may be touchier than you might expect. This zone has a lot of small but deceptively dangerous avalanche terrain at lower and middle elevations. Creek beds and road cuts create terrain traps where avalanche debris can pile up deeply, even from a small slide. Be alert to clear signs of instability in the storm snow today—cracking and collapsing in the snowpack are red flags that you've found unstable snow.

Avalanche Discussion

Yesterday's storm caused an impressive array of avalanches. Visibility was very poor throughout much of the day, and our observations of avalanches in the mountains are non-existent. But we didn't need to go into big terrain to find avalanches, they were coming down to the valley floor to meet us. Here's a quick rundown of some of the observed activity: 

  • Della Mountain west of Hailey avalanched in many locations, with multiple slides running to the valley bottom. One slide blocked and temporarily diverted the Big Wood River (photos and more details here).
  • At least three houses were hit by avalanches around the city of Ketchum.
  • Warm Springs Road was hit by a large avalanche and blocked by a slide path that hasn't slid in recent memory. 
  • A large natural avalanche was observed just outside of the ski area boundary at Bald Mountain. The crown of this avalanche was 3-4 feet thick (photo).
  • Dozens and dozens of roof-alanches were observed. Though relatively small, these can easily be deadly. 
  • Highway 75 was hit by numerous avalanches. The road was blocked by avalanche debris and remains closed as of this writing at 4 AM.
  • A large natural avalanche failed above the East Fork of the Big Wood River around 1 PM on Sunday. The powder cloud came down to the valley floor.

The storm has largely drawn to a close but very dangerous avalanche conditions remain. Think of the snowpack like a house of cards. Over the past few days, heavy snowfall and winds added cards to our house. In many places the house collapsed and was quickly rebuilt by the ongoing storm. Today, our snowpack house is teetering on the edge. An intense spit of snowfall, an uptick in wind speeds, or a trigger (you), will be all it takes to make it come crashing down. Please, continue to be safe and make good choices. Today is not the day for avalanche terrain.

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