Bulletin d’avalanche

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Danger d’avalanche

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

Points saillants

Avalanche conditions are dangerous, especially in the western portion of this zone (Dollarhide Summit to the Soldier Mountains). New snow + wind + weak layers in the snowpack = increased likelihood of triggering a large avalanche. Similar conditions over the past few weeks have produced several human-triggered and natural avalanches. Reduce your risk by sticking to gentler slopes, especially those sheltered from the wind.

Problèmes avalancheux

  • Persistent Slabs

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

    Over the past month, new weak layers (facets and/or crusts, and occasionally surface hoar) have formed in the upper portion of the snowpack. In response to seemingly continuous new snow and wind, these layers have produced several avalanches over the past two weeks (Dollarhide, Galena Summit, Smiley Creek, Beaver Creek, Sawtooths, Banner Summit). With yesterday's storm adding yet more weight, triggering an avalanche breaking in the top 3' of the snowpack will be more likely today—and don't forget that we still have weak snow near the base of the snowpack.

    What you shouldn't do: attempt to overthink/outsmart the problem. These weak layers present a complicated scenario, and even professionals are struggling to identify patterns. Some of the new weak layers have already produced avalanches, but others have yet to show their hand. 

    What you should do: take a step back and take a more holistic view. Recent loading due to new snow and wind? Check. Weak layers in the snowpack? Check. Recent avalanches? Check. When you look at it that way, the situation becomes more clear. Adopt the K.I.S.S. principle when choosing the terrain to play in: Keep It Simple & Safe. Triggering an avalanche will be most likely on upper elevation slopes steeper than about 35 degrees. Excellent skiing and riding conditions exist, and you can enjoy the new snow in a relatively safe manner on moderate slope angles on mid-elevation slopes sheltered from the wind. 

    The top 3' of the snowpack contains a number of weak layers that have formed over the past month.

  • Wind Slabs

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

    This zone has picked up 4-10" of low-density fluff since Thursday afternoon, with significantly more snow falling in the western portion of this zone. Not surprisingly, yesterday observers reported that the wind was easily transporting the new snow at upper elevations, and Soldier Mountain cat ski guides reported sensitive wind slabs. When low-density snow is blown into wind slabs and drifts, the difference in texture may be subtle. Drifted areas may still feel like powder, but may have just enough added cohesion that you could trigger a wind slab avalanche. Wind slabs may be forming atop weak old snow surfaces (facets and/or crusts) making them more reactive to your weight.

    Recognize that wind-loading also adds stress to the weak layers buried in the snowpack (described in Problem 1 above). Any wind slab you trigger could step down to these deeper layers, producing a much larger, more dangerous avalanche. 

    (2/20/2021) Ski guides remotely-triggered this wind slab avalanche on Peak 2 in the Soldiers while doing mitigation work. It broke 1.5' deep. Photo: Soldier Mountain Cat Ski.

Avalanche Discussion

Remember back to the first half of the winter when we had one exceptionally nasty facet layer, and we knew that each loading event would produce widespread avalanches and very dangerous conditions? Yeah...those were the days. Dangerous, but simple and predictable. 

Times have changed. On the whole, our snowpack isn't as hair-trigger, and dangerous conditions are less widespread. Unfortunately, the snowpack has become more complex and a much less predictable animal. Even though it's been a very snowy February, there have been sufficient intervals between the storms to create a number of new weak layers. The higher sun angle of late-winter has easily formed crusts, brief periods of clear and cold weather have created near-surface facets and surface hoar, and we've even had a few high-elevation rain events. 

As we move towards spring, these fast-forming weak layers usually heal quickly. But—as Scott points out in his Weekend Update—since late-January, portions of our area have received new loading from snow or wind 28 out of 31 days. This steady trickle of light to moderate loading continues to keep weak layers on edge. While avalanche activity has been less widespread than the massive cycles during the early-winter, there have been enough natural and triggered avalanches to know that several weak layers remain in play. There have even been a few slides where we've struggled to identify which weak layer was the culprit—and we do this for a living!

Realizing that snowpack conditions are exceedingly complex can be a relief in a way. It requires a shift in our approach to the problem—we can simplify the situation by going back to the basics. When I head into the backcountry today, this is what will be in the forefront of my mind: new snow + wind + weak layers + recent avalanches = dangerous conditions. 

Be sure to check out Scott's latest edition of our Weekend Update.

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