Lawinenlagebericht

Banner Summit

Sawtooth Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 7 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Human-triggered avalanches are likely in areas of recently wind-hardened and drifted snow. Look for obvious signs of unstable snow, like cracks shooting from your boards or sled. Avalanches may be triggered remotely — from gentle terrain above, below, and to the sides of steeper slopes.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    You’re most likely to trigger a persistent slab avalanche where recently wind-drifted snow sits atop one of the buried persistent weak layers that plague the majority of the forecast area. These layers are most prevalent at upper elevations and on shadier middle elevation slopes.

    Although obvious signs of instability are becoming less common, this problem isn’t going away any time soon. When dealing with persistent weak layers there are a couple of things to keep in mind: 

    1. Triggering avalanches remotely — from above, below, and to the sides of slopes, is a real possibility. 
    2. Persistent slabs can fail in surprising ways, break wider than expected, and span multiple terrain features that may otherwise contain storm slabs or wind slabs. 

    A small storm brought 3-6” of snow to the Banner Summit Zone last night although snow totals may quickly reach near a foot closer to Deadwood Summit. If you find yourself in a windier location, this new snow may have formed small sensitive slabs on the old snow surface. In areas with efficient wind-loading, it may have also increased the sensitivity of the underlying weak layers described below.

Avalanche Discussion

The primary weak layers in our snowpack are easy to see, but obvious signs of instability are getting harder to come by. Triggering avalanches, cascading whumpfs, and zippering shooting cracks can really drive home the message that the snowpack is unstable and dangerous. Despite a decrease in these warning signs, there are two primary weak layers that warrant your respect and attention:

  1. We buried a widespread layer of surface hoar in early December. We’ve found these weak, feathery crystals from Banner Summit, down through the Sawtooths and western Smokys, across the valley into the White Clouds, south to Galena Pass, further south into the Boulders, and in the mountains east of Ketchum and Hailey. In short, we’ve found it almost everywhere we’ve been.
  2. In areas that harbor lingering snow from September and October, large, sugary depth hoar sits at the base of the snowpack. This layer is more common in the Sawtooths, Western Smokys, White Clouds, northern Boulders, and Banner Summit area.

On Wednesday, we (the forecasters) had a meeting to discuss current conditions. We talked at length about the subtle differences in weak layers with changing aspect, elevation, and location. We also discussed the uncertainty of dealing with a widespread surface hoar problem – something that is rare in this area. Personally, I deal with complexity and uncertainty by dialing back the consequence of the terrain I choose to ride. Complex problems warrant simple terrain.

As the likelihood of triggering a slide slowly decreases, it can be harder to keep your guard up. Before committing to a slope ask yourself, “are one or more of these persistent weak layers present?”, and “what will the consequences be if I roll the dice and lose?”

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