Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Avalanche conditions are dangerous. Triggering a large, 3-4 foot thick avalanche is possible on most steep slopes—these slides may be unsurvivable. Stick to lower-angled terrain to reduce your risk. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    While the storm has ended and the Avalanche Warning expired, conditions are still dangerous. Triggering a destructive, 3-4' thick avalanche is possible on many steep slopes. The recent storm did not hit the Banner Summit zone as hard as further south, but it still received a decent thump of snow. This storm added significant weight to a persistent weak layer. In this zone yesterday, I found this layer on all aspects and elevations. Snowmobiling off trail, I watched snow shake out of trees 50' ahead of me as the snowpack collapsed. Snowpack tests produced poor results (photo above/right). These are clear indicators that triggering an avalanche is possible, if not likely. 

    The 3-4' thick slab sitting atop the November persistent weak layer is harder and denser than the rest of our forecast area. This dense slab makes it more difficult for our weight to affect the weak layer. But if we do trigger an avalanche, it would be a very dangerous, if not unsurvivable, slide. Conservative terrain choices are essential, and sticking to gentler terrain is the only way to avoid this avalanche problem. Given the possibility of remote triggering, pay close attention to the terrain above you.

    ADDITIONAL DISCUSSIONThe recent storm was accompanied by S-SE winds that blew strongly at times. Drifts and slabs that formed in wind-exposed terrain during the storm may remain sensitive. This problem pales in comparison to the persistent slab problem described above. If you trigger a wind slab, it could "step down" into more deeply buried weak layers and produce a much larger avalanche.

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

Avalanche Discussion

To keep track of all the avalanche activity produced by the weekend storm, the SAC forecast staff were all wishing we had the latest Intel Core i5 5GHz processor instead of our measly brains. I'm fairly certain all of us saw spinning beach balls and/or crashed and rebooted several times. If you're not a computer nerd, what I'm saying is that a lot happened over the past few days, and much of it came fast and furious.

With today's clearing skies, we'll start to get a better view of the avalanche activity produced by the recent storm. But even with the poor visibility the last few days, an impressive array of avalanches were reported. Many of these reached valley floors and impacted the urban interface. Here's a quick rundown of some of the observed activity: 

  • Yesterday, 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. 
  • 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. 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.
  • 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 near Galena Summit was blocked by an avalanche, but finally re-opened yesterday.
  • 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 ended, but the persistent slab problem isn't going away any time soon. The stakes are high—triggering an avalanche is likely, and it could be large enough to be unsurvivable. For the time being, conservative choices are essential and avalanche terrain avoidance is the name of the game.

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