Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Dangerous avalanche conditions exist. You are likely to trigger large, 2-3 foot thick avalanches in both sheltered terrain and in windier areas. Avalanches may be triggered remotely—from below, above, and to the sides of steep slopes.

Problemi valanghivi

  • Persistent Slabs

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

    We're only two days out from a storm that rapidly loaded a proven weak layer of facets buried in the lower third of the snowpack. A highlight reel of the recent natural activity, as well as yesterday's triggered avalanches and signs of instability, can be found in the discussion below. In summary, avalanche conditions are dangerous. For a great overview of what this problem looks like, check out Chris's video. 

    Last night's light snowfall and periods of moderate wind will keep an already stressed snowpack teetering on edge. Persistent slab problems are slow to heal. Large avalanches may be triggered in many areas, including terrain that's more sheltered from the wind. Remotely triggering slides from below, above, and to the sides of steep slopes remains a very real possibility. 

    Yesterday I observed a recent natural avalanche in the Soldier Mountains. It was a good example of how small, thin wind slab avalanches you trigger near ridgelines could "step down", failing on layers deeper in the snowpack. This scenario is a likely outcome across much of the forecast area.

Avalanche Discussion

Ah, where to begin! There's a strange mix of excitement and fear that occurs when my phone starts dinging rapidly as I get back to service after a day in the field. The fear, of course, is that something tragic has happened. This feeling of dread is slowly replaced by excitement, as I realize folks are okay and we've received some great observations to share in the next day's forecast. 

Numerous natural avalanches occurred during the storm Monday and Tuesday. Check out Scott's observation and the Avalanche Occurrences database to get caught up. The weak snow in the lower portion of our snowpack is well documented and a proven offender. With each storm, this stack of facets buried in mid-December produces natural activity followed by touchy (and frankly scary) avalanche conditions. 

Here are some highlights from yesterday:

  • Sun Valley Heli Ski staff remotely released three separate 3-6 ft deep avalanches when landing the aircraft in standard, safe landing zones. The slides released up to a quarter-mile away from the helicopter. They also observed dozens of natural avalanches in both wind-loaded and sheltered terrain. One notable trend was the collection of slides that failed in shallower, mid-elevation snowpacks on south and west aspects. 
  • Snowmobilers in the western Smokys remotely triggered this persistent slab from over 100' away. 
  • A public observer reported numerous slides in Pole Creek at the southern extent of the White Cloud Mountains.
  • Chris and Ben experienced a "huge collapse that sounded like a gunshot" (video, observation) and observed spooky snowpack structure in the Banner Summit Zone.
  • Ski guides near Galena Summit reported large collapses, some traveling up to 300', cracking in areas with previous ski traffic. 
  • Mitch and I observed a handful of avalanches on Peak 2 in the Soldier Mountains (video, observation).

Phew, that's a lot of bullseye data. The picture is clear–now is not the time to let your guard down. If you're used to dealing with persistent weak layers you know that this problem won't heal quickly. Last night's snowfall and periods of moderate wind are all it takes to keep the snowpack teetering on the brink of failure. Another round of snow tomorrow afternoon will continue to keep the snowpack on edge. Each of these small storms "resets the clock" as we wait for stability to slowly improve. 

Regioni coperte