Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

Sat
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

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.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    A storm earlier this week rapidly loaded a proven weak layer of facets buried in the lower third of the snowpack. With a deeper snowpack, avalanches in the Banner Summit area are less likely than in shallower areas to the south and east, but the resulting slides will be larger and more dangerous. For a great overview of what this problem looks like, check out Chris's video. A highlight reel of the recent natural activity, as well as triggered avalanches and signs of instability from across the forecast area, can be found in the discussion below.

    Continued 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. 

Avalanche Discussion

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. Since the storm, reports of remotely triggered avalanches, large collapses, and poor snowpack test scores continue to pile up. Here are some highlights from the last couple of days:

Yesterday

  • Skiers near Galena Summit remotely triggered this small persistent slab. All three observations from the Galena Summit area yesterday reported large collapses.
  • Scott and Ben found concerning snowpack structure and poor snowpack test scores while skiing the Boulder Mountains (video, observation). Similar results were found by another experienced group just to their south. 
  • Near Pole Creek Summit, Mitch and I experienced numerous large collapses including one that traveled well over 300' upslope. Signs of the recent natural avalanche cycle were everywhere. One public observer put it best "It seemed like no matter what direction you looked you could always see an avalanche" (video, observation). 

Wednesday

  • 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. 
  • 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. Another round of light snowfall and periods of moderate wind are expected this afternoon. Small storms are all it takes to "reset the clock" and keep the snowpack on edge as we wait for stability to slowly improve. 

Régions couvertes