Turnagain Pass

The last known avalanche activity was after the last big snow load on Monday (12/26) or Tuesday (12/27). There were several large avalanches along Seattle Ridge, with most activity coming from the southern end of the ridgeline near Peak 4940′. On the skiers side of Turnagain Pass there was an avalanche at lower elevations on Magnum that also looked large enough to bury a person. See ob here for more details.

East winds averaging 20-30 mph with gusts to 45 mph were building fresh wind slabs up to 2′ deep at upper elevations throughout yesterday. These lingering wind slabs will mostly be an issue in the alpine today, but there is a chance there was enough wind and dry snow around the top of the treeline elevation band to form some wind slabs there as well. To identify wind slabs pay close attention to the snow surface to look for areas that have been recently loaded. Getting off the beaten track to feel the snow surface can be very helpful to get a sense for how the wind redeposited the surface snow in the area you are travelling. Wind slabs will be most likely along upper elevation ridgelines or gully features. In areas sheltered from the winds we still have little information about how the new snow is bonding to the old snow surface. Due to that uncertainty we recommend a conservative approach if you get into the mountains today.

Lingering wind slabs in the upper treeline and alpine elevations are the main concern today. With about 6″ of new snow on the surface at treeline on Wednesday we could see wind slabs up to 2′ deep. Photo 12.28.22

Above the rain line from the last storm (2500 – 3000′) buried persistent weak layers could still be an issue. Prior to the last storm we were seeing skier triggered collapsing on a layer of facets above the Thanksgiving melt freeze crust that was buried about 1.5′ deep. With the addition of the new storm snow that layer is likely closer to 3′ deep now and could produce very large avalanches. In addition, we had weak faceted snow on the surface prior to the last storm on Sunday and Monday that could cause lingering instability at the interface with the new storm snow at upper elevations.

Triggering an avalanche on a deeper persistent weak layer is most likely in areas with a thinner and weaker snowpack. So far this year these conditions have been most prominent in the Girdwood Valley and near the southern end of Turnagain Pass, but it is worthwhile to have this problem on your radar across the forecast region. We recommend paying close attention for any collapsing in the snowpack and taking the time to check the snowpack structure in the area you are travelling to see if this weak structure exists. The best way to mitigate the risk from persistent weak layers is to make conservative terrain choices by sticking to smaller features and lower slope angles.

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