Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
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Avalanche danger

Thu
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Out of date — this forecast expired 4 years ago.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

Avalanche conditions remain scary. You could trigger a large, 3-4 foot thick avalanche—even in lower elevation terrain near the valley floors—on steep slopes. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes. Be careful. 

Avalanche problems

  • Persistent Slabs

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

    What is it?  A 3-4 foot thick slab overlies persistent weak layers (sugary facets, surface hoar, or crusts) on most slopes The slab is harder and denser near Banner Summit than in our other zones, making it a little less sensitive to triggering by skiers and snowmobilers. Slopes sheltered from the wind are suspect, and recently wind-loaded slopes are more dangerous. 

    Where is it?  The recent storm added to the slab everywhere, and the weak layers are widespread. Conditions are unusually dangerous in lower elevation terrain.  

    How can you recognize it?  This persistent slab problem is about as widespread as it gets; assume it exists on all slopes until proven otherwise. You're likely to experience snowpack collapsing and/or cracking while traveling. These red flags are obvious signs of instability. Wind-loaded areas feel stiffer under your skis or sled and keep you from easily sinking into the snowpack; these areas are especially dangerous.         

    How can you manage it?  Avoiding slopes steep enough to slide is the only surefire way to manage this problem.Persistent slab avalanches are tricky. If you're playing near steep slopes, you could trigger slides remotely (from gentler terrain above, below, and to the sides of steep slopes—explanatory video here). These avalanches may break wider than expected or higher on the slope above you. 

    (12/12/2022) In the Banner Summit zone, the weak November snow is buried beneath a 3' thick dense slab. 

Avalanche Discussion

While snowmobiling off trail on Monday, Chris watched snow shake out of trees 50' ahead of him as the snowpack collapsed. Snowpack tests produced poor results (photo above in Avalanche Problem section). These are clear indicators that triggering an avalanche is possible, if not likely. 

Yesterday's visibility window allowed all of us to check out the recent avalanche carnage in the zones south of Banner Summit (observation 1, observation 2). Of the countless slides we observed, many looked quite fresh (from Monday or Tuesday, after snowfall ceased). Undoubtedly, hundreds of avalanches released earlier in the storm but were hidden by additional snowfall and wind-loading. Dozens of slides reached valley floors, and several impacted the urban interface. Here's a rundown of some of the observed activity: 

  • Skiers and snowmobilers triggered or remotely triggered several avalanches in the past 3 days. Other parties reported large, loud snowpack collapsing in gentle terrain.
  • Monday, a skier was caught and carried by an avalanche on Scorpion, an out-of-bounds run near the Warm Springs base of Bald Mountain. Nearby skiers helped extricate him, and he was transported to the hospital to treat unknown injuries. Another group remotely triggered a large slide in the Trail Ck drainage near Ketchum.
  • A very large avalanche occurred in the Warm Springs drainage near Frenchman's Hot Spring (photo). This slide reportedly damaged a vehicle and a structure. Warm Springs Road was blocked by another large avalanche from a path that hasn't slid in recent memory. 
  • Della Mountain west of Hailey avalanched in many locations, with multiple slides running to the valley bottom. Debris blocked and temporarily diverted the Big Wood River, causing minor flooding and slush flows (photos and more details here).
  • At least three houses were hit by avalanches around the city of Ketchum.
  • A large natural avalanche was observed in the sidecountry or out-of-bounds terrain known as "The Burn" just outside the Bald Mountain ski area boundary. The crown of this avalanche was 3-4 feet thick (photo).
  • Dozens and dozens of roof avalanches were observed. Though relatively small, these can easily be deadly. 
  • Highway 75 near Galena Summit was blocked by an avalanche, reopening Monday afternoon
  • Multiple large natural avalanches (D3 in size) failed above the East Fork of the Big Wood River on Sunday, running over 2000 vertical feet to the valley floor.

The storm has ended, but the persistent slab problem has not. The stakes are high—triggering an avalanche large enough to bury you is possible. For the time being, conservative choices are essential and avalanche terrain avoidance is the name of the game.

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