Bulletin d’avalanche

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

Wed
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

You are most likely to encounter avalanches in areas where the wind has added weight to weak layers in the snowpack. These weak layers exist in the upper snowpack and near the ground. You can significantly reduce your risk of triggering an avalanche by choosing terrain that is sheltered from the wind.

Problèmes avalancheux

  • Wind Slabs

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

    Strong winds during last week's storm created a patchwork of scoured and drifted slopes. Where the wind was building slabs it did so on a variety of surfaces. These slabs have had a bit of time to bond to the surfaces that they were deposited on but there are still places where you can trigger them. On Sunday, on an off-duty ski day in the Sawtooths, my partner and I intentionally triggered a few small wind slabs in steep, alpine terrain. This type of terrain is unforgiving and you would not want to be caught on the wrong side of one of these slabs. 

    In this zone, these wind slabs are most concerning where they overlap with the persistent slab problems described below. Stiff slabs on top of weak layers (those in the middle of the snowpack as well as at the base) are never a good combination. 

    ADDITIONAL DISCUSSION A crust+facet combination exists underneath last week's storm snow on slopes that directly face the sun (southern half of the compass). I was in the Fishhook drainage yesterday where I observed several avalanches that appeared to have failed on this layer (photo at right/above, more photos here). Time will tell how long this layer will be problematic, but I'll be particularly leery of slopes where this layer exists for the next bit.

    (1/9/2022) Crown of a large avalanche that failed above the Fishhook drainage near the tail end of the recent storm. This slide likely failed on the crust+facet combination that was buried on sunny slopes by the recent storm.

  • Deep Persistent Slabs

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

    Weak October snow is buried 4-6+' deep on most shady middle and upper elevation slopes. Some sunnier, upper elevation aspects have this layer too. I dug down to this layer on Sunday in the Sawtooths and was not impressed by what I saw. The snow had shown some signs of healing, but I'm still a ways from writing this thing off. The recent storm event just added a huge load to this weak layer, especially on wind-loaded slopes. 

    I suspect you'd have to go looking for trouble to trigger a deep slab avalanche—but I wouldn't recommend that, since the consequences would be disastrous. Where might it still be possible to trigger a deep slab? I would still be leery of very steep (>35 degrees), rocky, wind-affected slopes at upper elevations and in alpine terrain. Large cornices collapsing and triggered wind slabs can make for very effective triggers for deeper weak layers. What does that look like? Have a look at the photo at right/above for an idea.

Avalanche Discussion

WEAK LAYER and SLAB DISTRIBUTIONAfter a wild month of nearly continual snowfall and wind we find ourselves in a period of clear skies, cold temperatures, and light winds. The calm after the storm. This is a great time to take stock of the state of the snowpack and think about the variability that we are seeing across our area. The first two rounds of storms (mid-December and near Christmas) brought a big helping of snowfall to most of our region. A bit more snow fell in our northern and western mountains (Banner Summit area, Sawtooths, Western Smokys, Soldiers) but the mountains above the Wood River Valley and those on the eastern side of the Big Wood and Salmon Rivers (Pioneers, Boulders, White Clouds) picked up their fair share. These storms buried a layer of weak snow that had stuck around after our first big snowfall of the year in late October. This October snow was preserved on shaded slopes at middle elevations and most slopes at upper elevations. The December snowfall pattern left a thicker slab of snow on top of this weak snow in the more favored areas (north and west) and a thinner slab to the south and east. Simple enough.

The most recent storm (January 3-7) heavily favored the northern mountains and left the good people of the Wood River Valley wondering, "storm, what storm"? In areas favored by this storm, we saw widespread avalanches related to the new snow (wind slabs, storm slabs, loose snow avalanches) as well as a pattern of activity that pointed to the involvement of a weak layer buried at the base of this storm snow. This layer appears to be at its worst on slopes that face the south half of the compass, where it exists as a subtle crust with facets above and below. In the areas favored by this storm, this layer is buried 2-3.5' down under a meaty slab of snow. In the areas that were missed by this storm, this weak snow is much closer to the surface. This is starting to feel a little more complex.

If we mentally zoom back out, we can see that we have patterns of weak snow and slabs that vary widely by aspect and elevation, and between forecast zones. If you want to completely avoid areas where either of these weak layers exists you will have to do quite a bit of thinking and planning. As the likelihood of triggering avalanches on these weak layers slowly decreases and the Avalanche Danger slowly comes down, we find ourselves in a tricky place. Avoiding avalanche terrain is pretty simple, but deciding when and where to engage with avalanche terrain is very complex. When you are out in the mountains today, think about these patterns and whether or not these weak layers exist in the terrain you are playing in. The danger may be MODERATE in all of our zones, but the snowpack is different everywhere you go. Whether or not you choose to enter avalanche terrain is up to you, just be sure you know what sort of dragons you are choosing to engage with.

Régions couvertes