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Know the Snow: Simple decision making and stability assessment

Posted: December 23, 2011 - 1:00am

Whenever I go into the backcountry, I use a holistic approach to evaluate the snowpack. I start to seek clues and insights into the state of the snowpack in the mountains with my morning coffee. I start my day checking recent weather and the forecast on the Internet (my first stop is Juneau’s National Weather Service website: pajk.arh.noaa.gov). On my way to the trailhead, I look around, searching for recent avalanche activity, check-in with friends to find out if they saw any avalanches, and often stop by the ski patrol to ask about results from recent avalanche control work.

As I skin, I pay attention to the way recent winds have redistributed the snow. I look to see if the snow surface is smooth, rough or shiny. Are there shooting cracks in front of my skis?

I listen to the sound of the snow as I travel: is it drummy? Does it make hashing sounds? Or does it collapse underneath me? I notice how much I sink into the snow and more.

To make sure I don’t miss important information, I remind myself of the article “Obvious Clues” by Ian McCammon (The Avalanche Review, December 2006). The article addresses the question: is there a classic avalanche accident pattern or it is just simple hindsight bias that kicks in? To better understand hindsight bias, think about an accident. Before disaster strikes, all outcomes seem more or less equally probable. But once the couch catches on fire, a buddy falls off the roof or a bar fight breaks out, the signals of impending doom seem obvious and the chain of events leading up the accident seems to have led inescapably to the outcome. This effect, known as the hindsight bias, is especially pronounced when we look at the actions of other people. McCammon examined avalanche accidents, looking for evidence of the well-recognized seven signs of apparent avalanche danger. The seven signs are:

• Considerable (a three on a one-to-five scale) or higher rating in the local avalanche forecast.

• Recent avalanche activity.

• Signs of unstable snow like cracking, collapsing or breaking train in deep snow.

• Playing in an obvious avalanche path.

• Present or recent snow loading from wind, snow, or rain.

• Terrain traps like cliffs, gullies or trees.

• Melting of the snow surface.

McCammon’s results suggest there is a consistent pattern in the majority of avalanche incidents. In fact, in more than half of the accidents McCammon examined, five of the seven obvious signs were present.

My practical experience has shown things start to feel serious when three of the seven clues are present. This is where I usually take a big breath, reassess my goals and evaluate my decisions carefully. When four of the seven clues are present, things start to get tricky; the situation starts to feel “out there,” margins of safety grow thin and finding a safer route starts to feel like a really good idea. Field experience indicates that when more than four clues are present, even experienced back-country travelers may have a hard time making it back home safely. In hindsight, the presence of four or more clues is precisely the conditions where I have had the majority of my near misses. Sadly, that’s where I have started to convince myself that things aren’t really that bad.

I like the three out of seven clues thresholds; it is a quick and simple tool that relies on basic observations rather than years of experience or detailed knowledge of snow science.

Unfortunately, we cannot forecast avalanches with a simple list of the obvious signs. It is only a reminder that one could be entering a situation similar to other situations where avalanche accidents have happened. Think about it as a well-thought-out checklist used to pack for a long trip — missing a few items from the list doesn’t mean the trip will fall apart. But if the trip does fall apart, it’s likely because some key items were overlooked.

When touring in the backcountry, I use this as a set point to “stop and reassess” the situation. Knowing when to stop and reassess is half the battle.

• Ron Simenhois is an avalanche forecaster who lives in North Douglas. You can contact him at ron.simenhois@gmail.com.

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