Lawinenlagebericht

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Sawtooth Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

You are most likely to trigger an avalanche where the wind has stiffened the snow above weak layers in the upper snowpack. While less likely, there is a chance of triggering an avalanche in very steep, wind-sheltered terrain. You can significantly reduce your risk of triggering an avalanche by choosing gentler terrain that is sheltered from the wind. Small natural and human-triggered wet snow avalanches will become possible on steep slopes that face the sun as the sun heats up the snow surface today.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Multiple human-triggered slab avalanches have occurred in the past week. All involved layers of weak snow in the upper 1-2 feet of snowpack. On Friday in the Baker Creek drainage, riders triggered three avalanches on subtly wind-loaded slopes. One of these was remotely triggered from the ridgeline above (photo, photo), a clear sign of the involvement of a persistent weak layer. I looked at these slides on Saturday and found that they failed 10-16" down on a layer of well-developed facets that formed during the mid-winter drought. A different weak layer—facets on a crust—was responsible for a  skier-triggered slide last Wednesday near the head of Smiley Creek. These slides are obvious indicators that triggering an avalanche involving this weak snow is possible.

    Both of these weak layers exist in this zone. The combination of weak layer+slab is not widespread, but where it exists it is possible to trigger an avalanche large enough to bury you. You are most likely to trigger an avalanche that breaks on these persistent weak layers where the wind has built a stiffer, denser slab on top of them. Moderate to strong winds over the past weeks have affected the snow in both middle and upper elevation terrain. While less likely, slabs failing in sheltered terrain can't be entirely ruled out. You can significantly reduce your risk of triggering a slide involving these layers by choosing slopes that are less than 35 degrees that are sheltered from the effects of the wind. Read more about this problem in the Forecast Discussion section below.

    ADDITIONAL DISCUSSION: 1-2" of snow fell in this Zone on Saturday night. Winds blowing out of the NW transported this new snow into small, isolated drifts that may continue to be reactive to your weight today. While small, they may be large enough to knock you off your feet, which can have higher consequences in steep, rocky terrain. Importantly, these slabs are adding weight to the buried persistent weak layers described above.

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–1.5

    Warm temperatures and a strong dose of spring sunshine will bring wet snow avalanches to the table today. The snow surface will start out with a solid freeze this morning, but the crust on top will break down as the sun climbs higher in the sky. Pay attention to the surface of the snow you are traveling on. If it is becoming wet and slushy and you are sinking in more than a few inches these types of slides will be possible. They will start out at a point and fan out as they travel downslope. These aren't likely to be large today, but they will be able to knock you off your feet or your machine and send you down the slope. This problem will be most likely on very steep slopes receiving direct sunshine where rocks and trees help to heat up the snow surface.

Avalanche Discussion

We find ourselves in a fairly unusual situation this spring. Oftentimes, by this point in the season, we are dealing with a simple and predictable snowpack. Unfortunately, the prolonged drought during the months of January and February and an upper elevation rain event at the beginning of March left us with a handful of weak layers in the upper snowpack. The presence and character of these layers varies from slope to slope and from Forecast Zone to Forecast Zone. What's more, instead of testing these weak layers with big storms we've been stuck with small storms that gradually build a slab of snow on top of these weak layers. This has provided us with little direct feedback about how these weak layers are reacting to the load along the way. That changed this past week.

The multiple human-triggered avalanches that occurred in the past 6 days are clear indications that avalanches involving these weak layers are possible. What makes this problem challenging is that we need the find the right (wrong) combination of the slab and weak layer to make these slides happen. On some slopes, the weak layers aren't weak enough while on others the slab isn't stiff enough. However, if you find the "Goldilocks zone" (like the skiers and riders did on Wednesday and Friday), you will find yourself starting an avalanche that you don't wan't to get caught in. 

So how do we deal with this? I must say, the answer is both frustrating and unsatisfying. The only way to completely eliminate your exposure to the risk posed by this problem is to avoid avalanche terrain where this problem exists.  Like I said, frustrating and unsatisfying. However, there are a few things you can do to significantly reduce your risk without completely avoiding avalanche terrain. You can limit (but not completely eliminate) the slab portion of this equation by seeking out terrain that hasn't been affected by the wind. Remember that the effects of the wind can be quite subtle and it can be hard to tell if the wind has been at work. Seeking out slopes that are a bit gentler (less than about 35 degrees) can also help you reduce your exposure to this problem. Don't forget that the danger is MODERATE for a reason today: human-triggered avalanches are possible. 

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