Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
Voir sur la carte

Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
Open full map
Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

You could trigger a wide, 3 foot thick avalanche. These slides are most likely in steep, rocky, alpine terrain that is affected by the wind. Avalanches may be triggered remotely—from below, above, and to the sides of steep slopes. 

Problèmes avalancheux

  • Deep Persistent Slabs

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

    The same layer of weak faceted snow that exists in our other zones also exists in the Banner Summit Area. The storm track this season has favored the Banner Summit Zone burying this layer under a dense 3' thick slab of snow. 

    The dense slab is making it more difficult for skiers and riders to trigger slides. However, if you are unlucky enough to trigger one, the resulting avalanche will be unsurvivable—large enough to snap trees and leave piles of debris many feet deep. Ben explains this situation here (video). 

    Deep slabs are unpredictable. You can trigger them from well down in the avalanche path, and after dozens of tracks have crossed the slope. You are most likely to trigger one of these monsters in steep, rocky terrain at upper elevations. In these areas, thin spots in the snowpack created by wind scouring and/or uneven ground cover bring the weak layer closer to the surface.

    The only way to manage a deep persistent slab problem is to avoid where it exists. Stick to lower-angled terrain and steer clear of slopes with runout zones that have trees, rocks, or terrain traps. Given the possibility of remote-triggering slides, avoid playing directly beneath rocky avalanche start zones.

    (1/18/2021) This very large avalanche occurred in our Banner Summit Zone, likely during last week's storm. Based on the depth and appearance of the crown it probably failed on facets buried deep in the snowpack.

Avalanche Discussion

Just about everywhere we look we see avalanches that failed during our last storm. In the last couple of days, we've observed avalanches in the southern tip of the Smokys (in the Soldier and Wood River Valley Zone) and in 4th of July Creek in the White Clouds.

In all corners of the zone (that hold enough snow), it's the same story; weak facets buried in mid-December.  The variable, and what's at the root of different problems and danger levels between zones is the thickness of the slab.

Banner Summit "Low Probability, High Consequence"This zone has the deepest snow. The Banner Summit Snotel station shows a snow depth of 4' at just 7,100' of elevation. In this area, the December facets are buried under 3' of heavy snow. The dense slab is "protecting" the weak layer, making it more difficult for skiers and riders to trigger slides. However, the outcome of triggering one of these beasts is grim at best. 

Sawtooths & Western Smoky Mountains, Galena Summit & Eastern Mountains "The Sweet Spot"With less snowfall than Banner Summit, these two zones have a snowpack structure that remains ripe for human-triggered avalanches. The slab over the December facets is about 1.5-3' thick. Thin enough in many areas to be likely to trigger, but thick enough to produce large and dangerous avalanches. 

Soldier & Wood River Valley Mountains "A Fine Line"This zone shows large variability in snow cover and problem distribution. Snow depth in the Soldiers sits at about 3', Dollarhide Summit in the Smokys is pushing 4', and Baldy along with many of the mountainous areas to the east of the Wood River Valley hover around 2'. This video from Croy Canyon on Tuesday shows a weak but generally stable snowpack that lacks a slab. Contrast that with this video of a healthier slab, poor snowpack structure, and unstable snowpack test scores from near Dollarhide Summit yesterday. 

Wherever you travel, it's important to keep the big picture in mind. At any location where you're finding snow deep enough to ride or ski, you'll find a slightly different flavor of this same problem. The most effective way to deal with this poor snowpack structure is to stick to lower angled, low consequence terrain. Before committing to a slope, look for terrain traps like cliffs, trees, and gullies that will increase the consequences of being caught. Don't let your guard down. This uniquely well-developed and widespread weak layer should be at the front of your mind.  

Régions couvertes