Turnagain Pass

We saw very touchy conditions for the second day in a row yesterday. With poor visibility along the road corridor in the morning and afternoon, we have limited info on yesterday’s activity. Here is what we know happened:

• Tincan: Yesterday was another good day of avalanche spectating on Tincan, with multiple natural avalanches during the day, and one remotely triggered avalanche in Common Bowl. Most of these were failing on south- to west-facing slopes. They were failing below Friday’s storm snow, which was sitting on a layer of surface hoar and near-surface facets on top of a crust. Crowns were 12-18″ deep, and the slabs were 100-150′ wide for the most part. Multiple avalanches released simultaneously in Hippie Bowl, indicating wide propagation at that weak interface. More information in observations here and here.
• Seattle Ridge: We have limited information from the backside of Seattle Ridge, but we do know there was at least one avalanche similar in size to what we saw on Tincan.
• Eddie’s: It looked like there was one fresh avalanche on the Eddie’s Headwall that either happened yesterday or in the middle of the storm on Friday.

Looking at all of the activity on the south face of Tincan from the Center Ridge parking lot. Red arrows are natural, purple arrow was triggered remotely from low-angle terrain connected to the slope that released. 04.02.2022

The snow that fell on Friday buried weak snow surfaces, and has been producing natural and human-triggered avalanches for the past two days. Yesterday we saw multiple natural avalanches in the Tincan area, and were triggering avalanches remotely from low-angle terrain connected to steeper slopes. The snowpack has shown that this latest round of storm snow is slow to heal, and it is likely a person will still be able to trigger avalanches 1-2′ deep today. The layer of concern is a thin layer of small buried surface hoar and near-surface facets that formed during clear weather on Wednesday. This layer appears to be most reactive on slopes that formed a crust ahead of the storm, but one group yesterday noted a clean shear in a test pit on a northerly slope that appeared to fail on a similar layer of surface hoar.

It is looking like we will see some periods of sun with mild temperatures today. As the snow surface heats up, expect to see increasing likelihood of natural and human-triggered activity. This was the case yesterday, and it is likely we will see similar activity today. So far these avalanches have not been huge, but we have seen multiple avalanches big enough to bury a person. There were multiple avalanches that were triggered remotely, or released sympathetically with other slopes, which tells us the weak interface has the potential to propagate wide distances. This might make it possible to see larger avalanches at this upper interface. Avalanches failing in the upper snowpack have the potential to step down to deeper weak layers, making for very large avalanches. More on this in problem 2 below.

With a reactive weak layer in the upper 2′ of the snowpack and warm temperatures and sunny skies contributing to deteriorating stability today, this is not the time to push it into steep terrain. Be cautious with your route finding today, avoiding traveling on or below large steep slopes.

These slopes in Hippie Bowl all released naturally, at the same time. This happened shortly after the sun popped out, and it is likely that one of the pockets released and triggered the rest sympathetically. W-SW aspect, 2800-3400′ elevation. 04.02.2022

We dug a quick pit at the crown of one of the natural avalanches to get a good look at the bed surface. It was hard to see with a naked eye, but under the lens there were clearly small surface hoar grains, along with near-surface facets on top of a crust. 04.02.2022

Wet Loose Avalanches: If we do end up seeing extended periods of sunshine today, we can expect to see wet loose avalanches on steep slopes exposed to the sun. These avalanches might pull out more slabs similar to what we saw on Tincan yesterday. Be on the lookout for warning signs of deteriorating stability on solar aspects, like rollerballs and pinwheels rolling down the slope as the snow surface heats up.

Cornices: These will also become more sensitive as they heat up today. A chunk of cornice falling on an avalanche-prone slope is a great way to trigger an avalanche. As always, limit time spent traveling under cornices, and be sure to give them plenty of space as you are traveling along ridgelines.

Glides:  We continue to see glide cracks moving throughout the area. Multiple glide avalanches have released over the past week, and the timing is impossible to predict. These avalanches are very large and destructive, so avoid spending time below these monsters.

We are still concerned with the deeper layers of surface hoar buried last month. These deep persistent slab problems have some nasty characteristics that make them very dangerous and very hard to manage:

• They seldom give feedback indicating unstable conditions prior to avalanching. This means our typical red flags (cracking, collapsing, new avalanches, unstable test results) will not always pop up before a person triggers a massive avalanche.
• They are stubborn to trigger, which can allow for multiple tracks on a slope before a person triggers an avalanche. It can also make it possible that a person gets way out into the middle of a slope before triggering a large avalanche.
• The slabs are thick, and they can propagate very long distances, making for very large and unsurvivable avalanches.

The avalanches failing closer to the surface (discussed in problem 1 above) have the potential to trigger a much larger avalanche down on these deeper weak layers. This is just one more reason to dial terrain back a notch today, limiting time spent traveling on or below steep avalanche terrain.

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