Turnagain Pass Avalanche Forecast

Seattle Ridge: A group taking an avalanche course watched a natural avalanche on the front side of Seattle Ridge yesterday. They also experienced large collapses and got propagating test results in snowpits at and below treeline.

Natural avalanche on the front side of Seattle Ridge. Photo: Joe Stock. 12.11.2021

Northwest winds will continue today at 10-20 mph, building fresh wind slabs that a person could likely trigger. These will be easier to find at higher elevations on the typical suspect features- just below ridgelines, convexities, or in gullies. The slabs formed by these moderate winds should be less than a foot thick, but there is a good chance that even a small avalanche triggered near the surface could step down to trigger a larger avalanche on weak snow buried 3-6′ deep (see more on this in problem 2).

Be skeptical of the terrain features mentioned above, and be on the lookout for signs of recent wind loading. This could look like a smooth, rounded pillow of snow or a rippled texture on the surface, and it will feel like stiff or punchy snow on top of softer snow. You may also notice warning signs of unstable snow like cracking or collapsing below fresh wind slabs. The dangerous setup below the surface will require treating these surface instabilities with a little extra caution.

Natural avalanche on a wind loaded slope at the top of  Zero Bowl on the back side of Seattle Ridge. This likely occurred a few days ago, but similar activity may be possible as winds blow today. 12.11.2021

Those of you who have been following the advisories for the past few weeks are probably well aware of the persistent weak layers of sugary facets lurking 3-6′ below the surface. As this layer gets buried deeper it is becoming more difficult to trigger, but we still need to approach it with caution. We are about 48 hours out from a major loading event where we saw large avalanches throughout the advisory area (check out more details and photos from Girdwood, Seattle Ridge, and Magnum/Cornbiscuit).

These layers are tricky because they usually won’t give you any kind of feedback before you trigger a large avalanche. It can be easy to get a false sense of security by seeing previous tracks on a slope, but we have recently seen avalanches on this layer getting triggered by the third or fourth person on the slope. We’ve also seen these avalanches triggered remotely, meaning that a person can trigger an avalanche without actually getting out into steep terrain. This requires an extra level of awareness, especially paying attention to the terrain above you. At this point an avalanche failing on this weak layer has the potential to be really, really big. We’ve seen them propagating thousands of feet wide and 4′-6′ deep or deeper. With consequences that high, we need to be extra cautious and avoid playing on or below slopes steeper than 35 degrees.

Natural slabs seen across Seattle Creek from the weather station. These failed during or just after the 12/9 storm. 12.11.2021

Large natural avalanche lower down on A1. Hard saying how deep it was looking at it from over on Notch, but it looked to be in the 6’+ range. 12.11.2021