Lawinenlagebericht

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Sawtooth Avalanche Center
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Lawinengefahr

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

Yesterday's storm built 1-2 foot thick slabs of wind-drifted snow that will be easy to trigger today and should be avoided. Periods of sun will melt the snow surface and bring on the potential for both natural and human-triggered wet snow avalanches. Avalanches breaking on the weak layers buried in the upper 1-3 feet of the snowpack may be possible even in areas sheltered from the effects of the wind.

Lawinenprobleme

  • Wind Slabs

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

    Yesterday's storm was an overproducer in the neighboring Sawtooths. Weather stations at the highway level here are reporting around 5" of new snow, but up higher there is likely a bit more. I was in Fishhook drainage of the Sawtooths yesterday where I found 8-10" of snow at 9,000'. Winds were easily transporting this snow and building slabs that were easy to trigger (photo at right/above). These slabs will be largest and most reactive at upper elevations.

    Expect to find these slabs along ridgelines and adjacent to cross-loaded terrain features. Look for signs that the wind has been at work and avoid these areas. Pillows and dunes of snow are a great indicator of this. If you are traveling through the terrain here and you find that the snow depth is increasing or that the new snow is becoming denser you've likely found a wind slab. Cracking in these fresh drifts are clear signs of instability. These slabs will be large enough to bury you and should be avoided today.

    ADDITIONAL DISCUSSION: PERSISTENT WEAK LAYERSSeveral layers of weak snow exist in the upper 1.5-3 feet of the snowpack. These layers appear to be at their worst on shaded middle and upper elevation slopes but the crusts and facets that exist on slopes that face the sun could be problematic as well. Avalanches that fail on these weak layers are less likely than the wind slabs described above, but would be larger and more destructive. The slab on top of these weak layers is now thick enough that these slides may be possible in terrain sheltered from the wind.

    (3/13/2022) This wind slab was intentionally triggered in the Fishhook drainage in the Sawtooths on Sunday, 3/13. It was 1-1.5 feet thick and failed at the base of the new snow. It failed on an E facing slope at 8,800'.

  • Loose Wet

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

    Wet, loose snow avalanches are very likely today. With that said, how bad this problem gets will depend entirely on the amount of cloud cover. I'm expecting we will see periods of high clouds blocking the sun as well as plenty of direct sunshine. Periods of clouds can press the pause button on this type of slide, but it doesn't take much March sun to melt the snow. Initially, these slides will have more of a dry character. The upper bit of the snow will melt and send the dry snow underneath cascading down the slope. As the day warms and the sun melts deeper into the new snow the debris from these slides will become wetter and more destructive. This problem will follow the sun—starting on E/SE aspects and wrapping around to S and then W as the sun moves across the southern sky.

    Pay attention to the snow surface and think about how the sun is affecting it. Is the powder you were skiing or riding in the early morning becoming wet and heavy? Are you seeing rollerballs coming down slopes that face the sun? These are all indicators that a wet snow problem is fast approaching. Thanks to the stiff crusts underneath the new snow they will be moving quickly and packing a punch. Pay attention to the terrain you are in as well as the terrain you are exposed to from above. This zone has a lot of steep terrain traps at lower elevations (like creek beds, etc.). If you are playing up high in cold snow, remember that you may have to travel through this type of terrain to get back to your rig at the end of the day.

Avalanche Discussion

FORECAST UNCERTAINTY

The uncertainty in today's forecast comes from three main sources:

  1. NEW SNOW and WIND: Weather stations at middle elevations are reporting about half of the amount of snow that was directly observed yesterday at upper elevations. This isn't uncommon, but it does make forecasting challenging. If you are up high in the mountains and you are finding less new snow than the forecast states, you will likely be finding safer conditions. Conversely, if you are seeing more snow than forecast and the wind has drifted it into slabs you may find more dangerous conditions.
  2. CLOUDS: Forecasting spring cloud cover can be a bit of a dice roll. Weather models are showing mixed clouds and sun for most of the day today, but it is looking awfully clear out my window here in Stanley... It won't take much sun to melt the new snow and create wet snow problems.
  3. BURIED WEAK LAYERS: Several different weak layers are buried in the upper portion of the snowpack. Due to a lack of loading over the past month it is unclear how much of a problem these layers will become. Yesterday's storm was a "great" test for this weak snow. We will have a better handle for how they behaved and where they are at their worst in the coming days, as we get out and see how much avalanche activity there was that involved this weak snow. Based on previous observations, these layers are at their worst on shaded middle elevation slopes, but there is reason to be suspicious of the crusts and facets that exist on slopes that face the sun as well. 

The first two items are relatively easy to deal with in the field. Pay attention to how much new snow you are finding and look for obvious signs that the wind has been at work. Are you finding big slabs, more snow than forecast, and evidence of wind transport? Simple, avoid steep slopes. The same goes for the wet snow problems. Watch the skies and monitor the surface of the snow. If the sun is out for long or if the snow is getting wet this problem is very likely and it is time to find a colder, shadier place to play. The buried weak layers are much more complex. The only way to be absolutely sure you don't run into this problem is to avoid the terrain where you might find it. Unfortunately, that describes quite a lot of terrain. Personally, I'm taking a big step back from steep slopes where these weak layers exist, particularly in places that just had a bunch of snow piled up on top of them. The only sure-fire way to deal with the uncertainty associated with these weak layers is to increase your safety margins until we know more.

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