In No. 10, I talked about a major dump of new snow that transitioned from great skiing to an increasingly touchy storm slab problem later in the day followed by an overnight cycle of natural avalanches.

By the morning after the stormy day, the natural cycle ended when the slab property (cohesion in the new snow), load (weight of the new snow), and bonds at a layer of plate crystals within the storm snow came to an uneasy truce—a situation forecasters refer to as “conditional stability.” Conditional stability means the snowpack is in balance: Natural avalanches aren’t happening, but it won’t take much in the way of change or a trigger to start avalanches or set off another cycle. We ran a more cautious program the second day but had still pretty good skiing in spite of the snowpack being near the tipping point. In this article we pick up the story as we came in from skiing on this day.

As is my routine, one of the first things I do at the end of my day is to look at the afternoon weather forecast. I saw little of little concern in terms of more snow, changes in temperatures, or potential solar radiation effects, but the forecast predicted wind would start in the evening and blow for 24 hours or so. Winds are notoriously tricky to predict in the mountains and our area is no exception, so I went to bed prepared to do a full update on our hazard analysis and risk-management plan the next morning.

The next morning, I noted the public forecast, issued the previous afternoon, predicted wind slabs. As soon as I stepped outside to have a look at conditions around the lodge, I knew things had changed overnight. In the moonlight, I could see dark green trees across the valley that had been snow covered the prior afternoon. Clouds were moving pretty fast across the sky and, even well below treeline at lodge elevation, it was breezy with drifts already visible in the yard. A review of nearby weather stations showed steady, moderately strong SW winds at upper elevations overnight and a bit of a mixed bag lower down with gusty SW, W, and NW winds.

Winds in general are a challenge in our area. The terrain is quite convoluted with features that cause twists and turns in the wind patterns, so it can be hard to tell where wind-blown snow has ended up. And the way the main valley lines up and funnels SW winds over our largely south-east and east facing terrain, a south-westerly produces a lot of cross-loading, which creates weird, disconnected slabs in the lees of even relatively minor gullies, rock outcrops, and clumps of trees. Under conditions like this, it’s easy to get caught by surprise if you’re not paying close attention.

In our morning meeting we all agreed we’d exceeded threshold wind speed—this is the minimum required to move snow and, while it varies depending on conditions, with recently fallen new snow it’s generally around 25 km/h. Given the upper flow was SW and steady both in terms of speed and direction, our hazard nowcast listed widespread wind slabs up to size 2.5 were almost certain on northeast-facing alpine terrain and smaller with less widespread, somewhat smaller wind slabs on adjacent east and north aspects. At treeline we figured we’d see mostly isolated, small wind slabs on a variety of aspects and noted cross-loading as something to keep an eye on. Below treeline, while the wind had blown there too, we figured wind slabs were unlikely, but the lingering storm slab might still be sensitive to skiers, especially in open glades. In addition, we expected cornices had grown and were likely not yet bonded.

This analysis, with several overlapping problems, was a major change from the previous afternoon when all we really had to worry about were storm slabs that were stabilizing. Just 12 hours of wind had created a much more complex risk-management challenge than what we’d been dealing with the last couple of days. And, given the winds were forecast to continue all day, conditions were quite dynamic—we predicted wind slab and cornice problems would become more widespread and more unstable with each passing hour.

This new situation required a pretty significant revision of our run list. Many of our bigger lee alpine features now were closed either due to on-slope wind slabs or overhead cornices. On the other hand, we were confident opening windward (south, southwest, west, and northwest) features, even large ones in the alpine where the recent storm snow would have been scoured off by wind. But we weren’t very excited about the prospect of skiing wind-hammered slopes, so even though they were green, we all knew these areas would be a less desirable fallback plan.

As we headed up the hill, we saw that cornices had, indeed, grown. Even though no new snow had fallen overnight, our tracks from the previous day were filled in on lee slopes. The snow surface had lots of wind ripples, drifts, and even sastrugi in some spots. In exposed areas, the storm snow from a couple of days ago had been stripped right down to the old snow surface, and most start zones lee to the wind had fat pillows of firm-looking snow in them. Overall, except in the most sheltered lower elevation terrain, it was clear the soft powder of the last couple of days was now anything from wind scoured to wind crust to wind slabs, depending on elevation, aspect, and terrain feature. There were no signs of natural overnight avalanches or cornice fall.

I started at treeline and was very careful on my first few runs. I skied short pitches from feature to feature, stopping my group above me each time the terrain shape or aspect changed. I had them keep an eye on me as I poked around, ski-testing small features with no terrain traps to assess conditions in places I suspected the wind had deposited snow. My ski-cuts produced minimal cracking but no significant results, even though I could clearly see and feel the wind slabs around me and under my skis.

This is my least favorite scenario. I knew the problems described in my morning theory existed—I could see and feel them. My analysis indicated there should be at least a few natural avalanches and skier-triggering would occur on more aggressive features. But I wasn’t seeing anything like this. So now, my questions were:

1. Was my morning analysis too conservative and could I push out a bit?
2. Had things not yet progressed to the tipping point, giving me a window of time in which I could ski a bit harder before it got worse?
3. Had I just not yet found the locations where the problem was most acute?

I consulted with my team and the snow-safety crew, and everyone was seeing the same thing, so I decided it was likely scenario B: the problem was there and likely deteriorating, but it was taking a bit longer than we had expected to get to the tipping point. So, I decided to head for slightly more aggressive terrain to get a couple more exciting runs in before having to pull back when things got worse.

And…. I promptly got my ass kicked.