Lawinenlagebericht

West Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

A mix of wet and dry snow avalanche problems will greet us on Wednesday, with sun breaks quickly producing wet loose avalanches on slopes directly facing the sun, which are areas to avoid when you notice the snow getting moist or rollerballs coming down. Meanwhile, over a foot of snow fell at upper elevations Monday night and Tuesday, and you could trigger dry avalanches in thicker drifts along ridgelines and around features. 

Lawinenprobleme

  • Loose Wet

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

    Dry, low-density snow will quickly become moist if we get sun breaks. On steep slopes, it will probably take only a few minutes from when the sun shines to when you start noticing rollerballs, which will then likely progress to wet loose avalanches.

    Stay aware of sky cover and snow moisture levels as you travel. Higher up, where the snow is over a foot thick, rollerballs will at first stay small, but if enough snow is entrained and wet loose avalanches run, an avalanche could be as deep as all the way down to the old snow interface. Below treeline, where a shallower layer of new snow sits over the moist underlying layer, expect to see swaths of the new snow layer running on the older layer beneath. Keep in mind that places you traveled earlier in the day may not be safe as the day progresses. 

    A wet loose avalanche running in the new snow layer down a steep slope, similar to what you will probably see on Wednesday. 

    Photo: Public obs

  • Wind Slabs

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

    You could trigger an avalanche in a wind slab on Wednesday.  Near and above treeline, slabs could be over a foot deep, although some new drifts could be shallower, with closer to 6" of snow avalanching with a human trigger. More than a foot of snow fell, and likely drifted into thicker deposits near ridgelines, around features, and in gullies.  We suspect the new snow layer bonded relatively well to the heavier, possibly moist, underlying layer, but newer drifts in the lower-density snow could avalanche with a human trigger. 

    Investigate the bond of the new snow over the old snow layer, or within new drifts of snow. Identify heavier or thicker-feeling snow, which may appear pillowlike or textured. Notice if your weight on the snow causes long, shooting cracks. If you find any of these thicker slabs, especially if there are accompanying indicators of weakness, steer around slopes steeper than 35° during your travels. There's a chance that a wet loose slide could step down, triggering a slab avalanche as well. 

    You could trigger a slab avalanche on steep rollovers in wind-drifted snow, like this recent example. 

    Photo: Jeff Tarshis

Avalanche Discussion

Over a foot of snow fell at upper elevations overnight Monday through Tuesday afternoon through much of the West Central zone. The underlying layer quite likely remains moist, but much of the new snow was cool and relatively low-density near and above treeline. Above around 6000ft the old snow layer will probably be heavier but it may not be moist. Freezing levels are forecasted to drop to 1000ft Tuesday night, but due to a thick layer of new snow over the moist old snow layer, we suspect the old layer will remain insulated, or "warm", and a crust isn't expected to form. 

Previous to the final push of cooler air which supplied us with the foot or so of new snow and inch+ of water, we received about 4" of water since Thursday. Most of this fell as rain, with the snowline mainly hovering in the 4000-5500ft range. We suspect that large, natural wet slab avalanches occurred over several days. Wet loose avalanches likely occurred many of these days as well. There is a small chance that glide avalanches could still run in suspect locations, which generally means steep, smooth rock slabs or grassy slopes. If you see glide cracks avoid traveling beneath them. 

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