Lawinenlagebericht

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Sawtooth Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 4 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Dangerous avalanche conditions exist and large, human-triggered avalanches are likely. Heavy snowfall and wind are building drifts and slabs that will be reactive to your weight. New snow is adding stress to layers of weak snow buried 1-4 feet beneath the snow surface. Avalanches that fail on these weak layers may be very large and can be triggered from long distances away from steeper slopes. These avalanches are most likely in terrain exposed to the wind, but are possible on sheltered slopes as well.

Avalanche Danger and the likelihood of triggering avalanches will increase throughout the day. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–2.5

    Several weak layers are buried in the upper 1-4' of the snowpack. Snowfall from yesterday and today is adding significant stress to these weak layers, and triggering a large slide involving these weak layers is likely. The nature of these weak layers varies by aspect and elevation, and the overlapping patterns are complex and hard to decipher. Crusts with facets, surface hoar, and near-surface facets—it's a safe bet that one or more of these layers exist on most slopes. Today is not a good day to try to thread the needle between them.

    We are just over a week out from a spate of natural and human-triggered avalanches that failed on weak layers in our snowpack (see photo at right/above, avalanche database here). These layers are again being pushed toward their breaking points today. Avalanches are most likely in terrain where the wind is building slabs, but large slides are possible in sheltered terrain as well.

    Persistent weak layers behave in ways that surprise even experienced backcountry travelers. Slides that fail on these layers may break much wider than you expect, wrapping around terrain features. Importantly, avalanches on these layers can be triggered from long distances away from steeper slopes. Pay attention to the terrain you are exposed to from above.

  • Wind Slabs

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

    7-9" of snow fell in this zone yesterday, and an additional 3-5" are forecast to fall by day's end. Southerly winds will continue to build 1-2' thick slabs in terrain exposed to the wind, and these slabs will be reactive to your weight today. Pay attention to the snow you are traveling through, looking for signs that the wind has been at work. Fresh cornices and ripples, dunes, and pillows are all signs of wind transport. If you are finding areas where the snow depth changes quickly you are likely traveling through wind-affected terrain. Cracks shooting out from your machine or skis are a clear sign that you've found a reactive wind slab. 

    Enough snow has fallen that these wind slabs will be large enough to bury you today. Any triggered slab could step down to the deeper weak layers described above, producing a larger, more destructive avalanche.

Avalanche Discussion

STEPPING BACK

Yesterday brought an intense, windy, quick-hitting storm to our area. Storm totals ranged from 3-9" of snow (0.25-0.7" SWE). We've got an even wetter, windier storm on tap for today. I'm expecting to see another 3-11" of snow (0.25-0.8" SWE) by sunset, with snowfall continuing after dark. Expect to find a wide range of storm-related avalanche problems today. Strong winds will build slabs in lots of terrain, which can produce sensitive slabs in places you don't generally find them. Stiff crusts from the Christmas heat-wave, the post-Christmas rain storm, and warm, sunny weather this week will help slides to pick up speed quickly. You will be able to easily trigger loose snow avalanches in  many locations. Many of these may be small, but these fast-moving slides can quickly knock you off your feet and drag you through some unpleasant terrain.

Of course, all of these storm-related problems are taking place on a stage set with multiple persistent weak layers. These layers produced a cycle of natural and human-triggered avalanches just over a week ago. The weak snow did not have much time to heal before the weather started throwing more snow and more weight on top. Small natural and triggered avalanches are effective triggers for these weak layers, and any slide that steps down to these layers will be large and destructive.

When we enter the backcountry, we can give ourselves a big advantage by doing so with a particular mindset. When the weather is actively changing, and our snowpack has proven weak layers, we're well served to go into the field with a mindset of stepping back. The last week has brought gradually decreasing avalanche hazard in our mountains and lots of folks have been pushing into steeper terrain. Today is different. With intense precipitation rates and strong winds we will see the likelihood of triggering large slides increasing as the storm progresses. In a sense, things are simpler today. This isn't a day to try to thread the needle between the myriad avalanche problems that are going on out there. Its a good day to take a big step back, enjoy the skiing and riding on low angle terrain, and let the dust from these storms settle.

 

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