Bulletin d’avalanche

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Sat
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

New snow and wind are creating dangerous avalanche conditions–particularly in the White Clouds. You’re most likely to trigger a slab avalanche in freshly formed wind drifts. Underneath these drifts, weak snow buried near the ground continues to pose a threat. To reduce your risk, steer clear of slopes where the wind has stiffened the snow surface. 

With less recent snowfall, the danger is lower to the south and east of Galena Pass.

Problèmes avalancheux

  • Persistent Slabs

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

    Monday's wind event produced several large, natural persistent slab avalanches in the Boulder Mountains (see observation and photos below). Similar avalanches are possible again today, particularly in the White Clouds which received more recent snowfall. Ben visited an avalanche that released Sunday in the White Cloud Mtns (photo to right). It broke over 500 feet wide, 4-6 feet deep, and wiped out the majority of the season’s snowpack, covering snowmobile tracks from the previous day.

    What are the common threads in the recent avalanche activity?

    • Steep: slopes in prime-time avalanche terrain around 35-45 degrees.
    • Wind-loaded: heavily wind-loaded by recent wind events.
    • Alpine flavor: complex terrain with rock ribs, cliff bands, or minor ridges near the avalanche crowns or flanks.

    The consequences of a triggering a destructive, 2-6 foot thick, persistent slab would be severe. Be aware that even if you aren’t in steep terrain yourself, the snow that you are traveling on may be connected to that sort of terrain above you.

  • Wind Slabs

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

    Galena Summit tallied about 8” of new snow since Wednesday. Although we don't snow depth data for the White Clouds, I’d expect this number to be closer to a foot. This snow accompanied by moderate to strong NW wind built wind slabs in exposed terrain. Yesterday, small slab avalanches were triggered in the central Sawtooths, near Galena Summit, in the Boulder Mountains and in the Wood River Valley. Expect to find touchy wind slabs again today, especially as you climb into more wind-affected terrain at upper elevation. 

    These slabs will be most sensitive where they are sitting on firm surfaces, like crusts or older hard slabs. Ripples, dunes, or wave-like patterns can help you identify freshly loaded slopes. Cracks in the snow surface are a sure sign that the slope you’re on is unstable. A shallower wind slab that begins near the surface has the potential to break into deeper weak layers of snow near the ground (see above).

Avalanche Discussion

There are two avalanche problems to contend with today: freshly forming wind slabs at the snow surface and persistent slabs that have the potential to break on weak layers in the lower half of the snowpack. 

We’ve topped a foot of new snow in areas around Banner Summit, the Sawtooths, the White Clouds and the western Smokys. The hazard posed by new snow and wind is relatively straight-forward. Fresh drifts will be sensitive to your weight, and if you venture into windier upper elevation terrain, the snow stinging your face will be a good reminder to keep wind slabs at the top of your mind. 

Less obvious are the hazards that lurk below. The weight of new-fallen and wind-blown snow will stress weak layers deeper in the snowpack. Over the weekend and earlier this week, these layers proved they weren’t quite ready to go away quietly. Persistent slab avalanches were observed in the White Clouds, the Boulders, and the Pioneer Mountains. Similar avalanches are possible again today, particularly in areas where storm snow overloads a shallow weak snowpack.

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