With spring storms, the properties of the slab change quickly. Snow often falls on a crust, and more and more slab avalanches are triggered.
Sarah Carpenter, BCA ambassador, AMGA Guide, and lead avalanche instructor for the American Avalanche Institute based in Jackson, Wyoming, knows a thing or two about teaching people how to travel in the backcountry. And for BCA's springtime guide to safety, we caught up with her to hear what she thinks about keeping travel safe when days lengthen and weather begins to transition to the warmer seasons.
BCA: Why don't you start by telling us how spring has different challenges and how to approach them and deal with them.
Carpenter: Off the top of my head, things that come to mind are that oftentimes spring comes earlier to the valley than it does to the mountains. And I feel like I have seen a lot of accidents where we're experiencing spring down in the valley, but the mountains still have a cold winter snowpack. We've had some accidents in the Tetons where everyone's running around in flip flops in the valley, but then people walk up into a cold winter snowpack and trigger an avalanche that they didn't expect to trigger. I think not transitioning to a spring mindset super early is essential.
The other thing I think about with spring storms is that the powder skiing lasts for a shorter amount of time, and the slab becomes cohesive quicker. And so I also feel like I've seen these accidents where we get six or eight inches of snow, and in mid-winter, we're just powder skiing and having a great time because it's not a significant load. But in the spring, the properties of the slab change so quickly, and it often falls on a crust, that I feel like we've seen more and more slab avalanches triggered and accidents happen in those conditions.
BCA: Is there anything in particular that you change about your travel habits?
Carpenter: I think the obvious habit I change is how early I leave for an objective. This is your classic get up at two in the morning and be back at the Trailhead at 11, having had a full day. I also find myself packing ski crampons and other sharps because things are so much firmer. I tend to pack way more water as well because it gets so warm, and I get thirstier.
When I think about spring and spring snowpack and spring missions, I think about the processes of the snowpack shifting where we're not focused on how much weight and how much load is added to a snowpack, but we're thinking about how much strength is taken away from a snowpack. I feel like it's just really different forecasting. We're looking at has it melted? Did it freeze overnight? How long did it freeze? The process of seeing avalanches is often that we're taking away strength rather than adding stress via new snow. Everything gets flipped on its head.
BCA: What kind of objectives do you shoot for in the spring, and does your process change at all for analyzing your approach?
Carpenter: Well, in the spring, it feels more common to go for bigger objectives, although sometimes in the winter, it can be more straightforward forecasting. When spring hits, I often go to the higher peaks and ski the bigger lines. My decision-making isn't just on snowpack and snow conditions; it's also on the fall hazard. And I look at terrain a little differently. I'm still looking at the consequence, and my likelihood calculation isn't just the likelihood of triggering an avalanche but also the likelihood of a fall in committing terrain. There are times when the cloud cover or cold temperatures might turn me around from my objective in the spring.
BCA: Do you have any advice for people looking at this spring season as a chance to get out into the mountains and really explore?
Carpenter: I would say start small, which is easier said than done. If you're pushing up into higher elevation terrain, maybe don't start with the biggest, gnarliest steepest objective. Start with more manageable terrain. Get a sense of the conditions, ask yourself: "Do we have a spring or summer snowpack up high? Or are we still dealing with winter?" Because then you understand what you're forecasting for, at least for a little while. You need to take a much longer-term vision of goals and objectives. It shouldn't be a season-long vision. It should be a lifelong vision for big objectives. This year in the Tetons, we've had a pretty low snow year, so some of the lines aren't in, or they've had a lot more slide for life conditions. And so, if you can take more than a season-long perspective, it can help you in your longevity in the mountains.
As you're stepping out into bigger and bigger objectives --- make sure you're doing it with partners you know and trust. If you're skiing with new partners, "try before you buy." In the Tetons, my example would be to tour on Teton Pass with someone before you go into the Park to ski a bigger line with a new partner. Make sure you can communicate with this new partner, make sure your risk tolerance is similar, or that it's appropriate. Make sure their skill set and your skillset align. That, to me, is a really big one.
If your forecast center has been talking about persistent slab avalanches all winter, pay attention if they start talking about wet slab avalanches in the spring. The structure of that persistent slab avalanche problem can lead to wet slab avalanches, and wet slab avalanches are really hard to forecast. And the harder a problem is to forecast, the bigger the margin I want to give myself.