Turnagain Pass

With sunshine in the forecast today travel into the Alpine will be appealing. Keep in mind triggering a fresh wind slab around a foot deep will be possible. Yesterday there was steady snowfall throughout the day with 2-6″ of accumulation, favoring Girdwood. With this there were easterly winds that were sustained at ridgetops, 15-25 mph with gusts into the 30s and 40s. Blowing snow and fresh wind slab formation was observed. In the evening the snow shut off and the winds shifted to the west/northwest blowing 10-15 mph with gusts into the 30s. These are forecast to continue throughout the day peaking in the late afternoon. Today wind slabs will be possible on all aspects. Figuring out which slopes are loaded might be complicated. The east winds impact Turnagain terrain more significantly than the west/northwest winds. However, it is important to remember west/northwest winds can funnel through the Pass from the south and load north aspects on the non-motorized side, while at the same time load the SE face of Seattle Ridge. This wind pattern also increases through channeled terrain and can be more pronounced in Crow Pass and Portage. Pay attention to blowing snow and active wind-loading.  There may also be old lingering wind slabs from the past wind-loading events as well. Look for smooth pillowed snow on convexities, cross-loading in gullies and feel for stiff snow over softer snow. As always, watch for signs of instability like shooting cracks from your skis or machine.

If you do find and trigger a new wind slab, remember it could step down to old buried weak layers deeper in the snowpack. In this case, a larger avalanche is possible (more on this in Problem 2).

Cornices: When traveling along ridgelines be sure to give cornices plenty of space, and minimize the amount of time spent traveling below them. Cornices could fail under the weight of a person on skis or a snowmachine, and might trigger an avalanche if the slope below is wind-loaded.

Sluffs: It will be easy to trigger loose snow avalanches (sluffs) in steep terrain that has been sheltered from the winds. It is unlikely an avalanche like this would be big enough to bury a person, but they can have serious consequences if they carry you into terrain traps like cliffs, rocks, or trees.

Cracking on a wind-loaded small slope yesterday, 2.24.21 on Eddies. Watch for cracking and drifted snow today.

For video click HERE.

We continue to track two weak layers of snow (surface hoar and facets) buried in the top 2-3′ of the snowpack. You may be feeling a bit of message fatigue as we have been talking about these layers for close to a month. However, the data continues to point to the potential for these layers to fail and cause an avalanche. There have been avalanches in the past week that have failed on these layers and snowpack test continue to show instability. We know these layers are present in most areas and in all the elevation bands, but they are not reactive everywhere, which makes it complicated. The new snow and wind-loading could add a little more stress to the snowpack. There may be old hard wind slabs sitting on top of the weak layers allowing you to get well out onto the slope before it fails or failing after other machines or skiers have have already ridden the slope. Triggering a fresh wind slab or cornice fall may step down to one of these buried weak layers. As we have said before, this snowpack has to be viewed with some uncertainty and caution.  If choosing to push into steeper terrain, keep in mind that these weak layers exist, watch for signs of instability (with the caveat that they may not be present but the slope may be unstable), follow safe travel protocol and evaluate terrain consequences.

Snow pit at 1200′ on Eddies, 2.24.21. Note the buried weak layers and that they propagated easily with not much force.

Snow pit @ 2000′ on Eddies, 2.24.21. This was in a spot with wind hardened snow above a layer of buried surface hoar. The extended column test took more force but still showed potential for an avalanche to be initiated, ECTP23.

On steep southerly slopes especially at lower elevations expect roller balls and small natural wet loose sluffs as sun hits the new snow. The colder northwest winds may keep things cool in the Alpine but wind protected rocky areas in the direct sun may also see some activity. The roller balls and small wet loose sluffs could also be human-triggered if you find yourself traveling in steep southerly terrain. It’s that time of year where aspect in relation to solar gain will start to play a role in avalanche conditions. Keep that in mind as the we move into March!