Lawinenlagebericht

Soldier & Wood River Valley Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Dangerous avalanche conditions exist. Triggering an avalanche that fails on weak snow buried 1-2' deep remains likely on most slopes—especially in wind-drifted terrain. Avalanches may be triggered remotely—from below, above, and to the sides of steep slopes. Skiers and riders remotely triggered avalanches in neighboring zones both days this weekend.

Lawinenprobleme

  • Persistent Slabs

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

    Snowpack depths vary significantly across this zone. Unfortunatley, a disturbing constant exists on all snowy slopes: the weak snow buried in December forms the base of the snowpack. Snowfall over the past month has favored the western side of this zone (Soldier Mountains, Dollarhide Summit, S Fk Boise River). Here, the weak snow that developed in December is buried by a 1.5-2.5' thick slab of snow. On Friday, Soldier Mountain Cat Ski guides remotely-triggered an avalanche that appears to have failed on this weak snow (photo here). 

    Further east in this zone, in the mountains above the Big Wood and Little Wood Rivers, a very thin snowpack exists. On many slopes, what little snow has fallen has been removed by wind and snow. On shaded slopes and those sheltered from the wind, weak early season snow is creating dangerous avalanche conditions (photo at right/below). In areas sheltered from the wind, this weak snow is only buried about 1' deep. However, in areas loaded by the wind this slab can be thicker, as was the case in the avalanche pictured to the right.

    The picture is simple, but its far from satisfying. Dangerous avalanche conditions exists and you are likely to trigger a large avalanche on most steep slopes. The only way to avoid the hazard posed by the weak snow at the base of the snowpack is by sticking to lower-angled terrain. Given the possibility of remote-triggering, you'll also want to avoid being below steep slopes. 

    (1/17/2021) This avalanche failed in the mountains above the Wood River Valley on a N facing slope at 8,000'. The culprit weak layer was the same weak, sugary snow that exists across our forecast areas. The slope had been heavily loaded by the winds of the past week.

Avalanche Discussion

One important variable that we consider when assessing avalanche hazard is the amount of time that has elapsed since a load was placed on the snowpack. In our case, the last major snowfall occurred six days ago. Following this storm, strong to extreme winds easily pushed around the snow that fell. In some places, winds were strong enough to blow the snow off into the atmosphere while in others it loaded slopes. This additional loading produced a second round of natural avalanche activity. It has now been a few days since we've observed active wind-loading, which has given the snowpack a bit of time to adjust to the additional stress.

Generally, a few days without loading is a healthy break for the snowpack. If we were dealing with a strong snowpack without weak layers, the avalanche hazard would lower right now. However, the sugary, faceted snow buried near the ground in our region is anything but strong. This widespread layer of weak snow has been buried for over a month, and each time we add more weight with a storm we see widespread natural avalanche activity. Equally importantly, each time we add a trigger to the mix (riders, skiers, you!) we are seeing human-triggered avalanches continue many days after loading. Our snowpack doesn't need a weekend off, it needs a long vacation on the beach. 

The backcountry is what is known as a "wicked learning environment." Environments like this provide feedback that is either difficult to interpret or altogether nonexistent. For example, your partner decides to ski a steeper line than you had agreed upon and nothing bad happens. Does that mean that the slope was actually safe and that the decision was a good one? Well, no. And therein lies the problem—the only direct feedback that we get from the snow is when it avalanches. The absence of an avalanche is not a sign of stability. And once we trigger an avalanche we have set ourselves up to learn some hard lessons.

Today will be a beautiful, calm, sunny day. The lure of steep, untracked slopes will be strong. But the weak snow that is buried in our snowpack is not in any hurry to heal and today is not significantly safer than yesterday. We continue to encourage you to make your decisions in the backcountry with this weak snow in mind.

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