Avalanche forecast

Central Cascades

Central Oregon Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Triggering avalanches in wind-deposited snow will be likely at upper elevations on Thursday, and will be possible at mid-elevations on open slopes and below ridge tops. Avalanches within the recent storm snow are becoming less likely, but could still be possible on Thursday in isolated areas or very steep terrain. If you're venturing up high, evaluate the snowpack carefully before committing to slopes that are steeper than 30 degrees. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Although new snow on Wednesday was minimal, wind speeds were moderate to strong throughout the day at upper elevations. I also observed blowing snow along ridge tops and open areas at Tam Rim on Wednesday. Winds have been predominantly out of the west and northwest over the past 24 hours.

    Wind speeds are expected to decrease on Thursday morning, with light westerly winds through most of the day. However, wind slabs that formed during the recent stormy weather will need more time to bond to the snow underneath, especially at upper elevations on slopes that got more loading. With the recent stormy weather, we don't have a lot of information about conditions in the alpine. Whenever we have uncertainty about snowpack conditions, it's good to give yourself a bigger margin of safety. 

    If you're traveling up high on Thursday, use extra caution at upper elevations and avoid large, open wind-loaded terrain, where wind slabs will be larger and more likely to trigger. Looking for smooth, pillowy or rippled texture on the snow surface is a good clue of a wind slab's presence. You can also use your pole to probe into the snow and check the depth of wind deposits, or feel for strong over weak layering. Finally, give cornices a wide berth on Thursday. 

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1–2

    On Wednesday, we didn't get the expected snow accumulation to develop a new storm slab problem. There are a few instabilities within the upper layers of the snowpack, but the layer that I was investigating today is down about 40-55 cm, between the most recent storm snow and the older storm snow from earlier this month. This is the same layer that resulted in the Happy Valley avalanche on Monday. 

    At Tam Rim today, I was able to find this layer of weaker snow on north, west, and south aspects between 6700' and 7400'.  In compression tests, this layer failed in moderate to hard taps with resistant planar fracture character. Extended column tests did not produce propagation. The snow grains in this weak layer were decomposing fragments that were starting to round (i.e., not faceted grains). I was not able to find the melt-freeze crust that served as the bed surface in Monday's avalanche accident. 

    All of this is to say, the storm slab problem is becoming increasingly stubborn, but I'm not ready to rule it out just yet. I will continue to use my ski pole to probe into the snow and dig to monitor the upper snowpack. I will also keep looking for that melt-freeze crust on aspects that may have gotten sun last week. 

    Conservative travel techniques like riding one at a time in avalanche terrain and avoiding terrain traps like cliffs, gullies and tightly spaced trees are a good idea while we give this layer a little more time to heal. 

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