Bulletin d’avalanche

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Thu
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 7 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

You are most likely to trigger slab avalanches on slopes where the wind has formed drifts or stiffened the snow near the surface. These conditions are widespread at upper elevations but become easier to spot and avoid as you drop in elevation. Even though it hasn’t snowed in awhile, you may be able to trigger slides remotely — from gentle terrain above, below, or to the sides of steeper slopes.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    The odds of triggering an avalanche are slowly decreasing each day that we don’t receive snowfall. But, terrain with both a buried persistent weak layer (surface hoar or sugary facets)  — most upper elevation and many middle elevation slopes  — and recent wind-loading or wind-stiffened snow at the surface — many upper elevation and some middle elevation slopes — are plenty capable of producing slab avalanches. Triggering avalanches is much less likely in terrain sheltered from the wind. 

    Avalanche center, professional, and public observers have not reported any new avalanches in the past couple of days, but they continue to note obvious signs of instability (collapsing, cracking, and whumphing noises) throughout most of our Forecast area. A regular public observer playing near Pole Creek (where the White Cloud and Boulder Mountains meet) on Monday experienced widespread collapsing and whumphing noises in flat terrain, noting they “haven't seen this much activity in years.”

    If you experience red flags (collapsing and cracking) or just want to minimize the chance you’ll trigger a slide, avoid wind-loaded slopes and/or stick to gentle terrain. If the snow surface isn’t “blower powder”, you’re on a wind-affected slope. Given our widespread persistent weak layers, triggering avalanches remotely — from gentler terrain above, below, or to the sides of steeper slopes — remains a real possibility. Learn more about our snowpack and these weak layers in the Forecast Discussion section below.

Avalanche Discussion

We need three ingredients to have an avalanche: a weak layer, a slab, and a slope. 

  1. The weak layer: We have persistent weak layers, in spades. We buried a widespread layer of surface hoar in early December and have seen extensive avalanching following each storm since then. We’ve found these weak, feathery crystals buried 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. The avalanche near Miller Creek in the Soldiers likely involved this layer too. In short, we’ve found it almost everywhere we’ve been. The nature of the snowpack varies widely across our forecast zones, but this layer is an ugly constant. The surface hoar is most widespread on shady and partially shady aspects, but we have seen it regularly on sunny aspects too. We also have a depth hoar issue in the northern and western mountains, areas that harbor lingering snow from September and October storms. Many upper elevation and shady middle elevation slopes have both of these weak layers. Ouch.
  2. The slab: The northern and western Zones received a healthy dose of snow and wind with the last storm, forming widespread slabs. The Wood River Valley did not receive as much snow, so slabs (and avalanche activity) were not as widespread.
  3. The slope: This is what you control. You can assume as much or as little risk as you want; it’s your choice. Where you have both a slab (wind-loaded terrain) and a persistent weak layer (most upper elevation and many middle elevation slopes), playing it safe by avoiding avalanche terrain is prudent. Sorry to be the bearer of bad news.  

Going forward: The widespread buried surface hoar problem is a rare occurrence in this area, meaning none of us have a lot of experience dealing with it. We don’t have the “personal databases” to be able to accurately predict how individual slopes will behave when we load them during small to medium-sized storms in the coming weeks. Avalanche forecasting — and playing in avalanche terrain — is all about minimizing uncertainty, and there’s a lot of uncertainty on the horizon. Buckle up for a bumpy road ahead. 

Régions couvertes