Lawinenlagebericht

Central Cascades

Central Oregon Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

We're mid-storm, and triggering avalanches will remain likely on Sunday. The avalanche danger will be highest in terrain where the wind has deposited new snow. Avoid steep, open slopes and cornices. If you're in forested terrain, steer clear of the steepest parts of the slope, as well as cliffs and gullies.

Lawinenprobleme

  • Wind Slabs

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

    With up to 10 inches of new snow on the way and sustained 15-20 mph winds on Saturday night, we can expect wind slabs to continue developing overnight and into Sunday. Wind slabs are characterized by rippled or smooth snow surface, drifts and wind lips, cornices that are getting larger, and plumes of snow at ridgetops or moving along the snow surface. Wind slabs have the potential to be large enough to bury, injure, or kill a person on Sunday.

    Winds are forecasted to be from the southwest, though they could shift to the west and south. On Sunday, look for wind slabs on on northwest through south aspects. You will most likely find this avalanche problem just below ridgetops and on open slopes at upper elevations. However, it's a good idea to watch for signs of a wind slab problem in any terrain that can catch windblown snow, such as open glades or burned forest.

    If you're unsure whether a slope is wind-loaded on Sunday, it's best to avoid it.

    On Saturday at Tam McArthur Rim, it was easy to find evidence of a wind slab problem. As I toured into open terrain and along ridge tops, I could see ripples on the snow surface. I also noticed that the snow under my skis felt denser (I wasn't sinking in as much), and the snow cracked and broke under my feet. I used the handle of my ski pole to probe into the snow to the rain crust from last weekend. In the forest where the snow was protected from the wind, I measured 35-45 cm of new snow over the crust, and up higher on a lee slope below a ridge, there were 65-70 cm of snow over the crust. These changes in snow depth and density tell me that wind slabs are present. 

    (12/14/2024)

    Rippled texture on the snow surface on Saturday, 12/14/2024, at Tam McArthur Rim. 

    Photo: Allison Miles

  • Storm Slabs

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

    Sunday's storm slab problem will depend on how much new snow falls and how well the layers within the new snow stick together. If we receive the higher end of the forecasted snow totals (up to 10 inches), the storm slab danger will go up. Storm slabs can exist anywhere in the terrain the wind hasn't moved the snow or scoured the surface. 

    As the snow stacks up, look for cohesive layers of snow that are easy to break apart. Hand shears and shovel tilt tests are a good way to quickly assess the snow layers near the surface. Walking over small convexties within low-angle terrain is another easy way to test the top of the snowpack. I like using my ski pole to ascertain the snow density and see whether there is dense (strong) snow over less-dense (weak) snow. On Sunday, ease into the terrain by starting with low angle slopes and avoiding the steepest part of the slope, including convex rolls, until you can rule out the presence of storm slabs. If you're not sure, keep it low angle. 

    There were reports of small, skier-triggered storm slab avalanches on Friday. On Saturday, I noticed some instabilities within the recent storm snow while conducting hand shears along the skin track and walking over convexities. 

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