What is “CONSIDERABLE” danger?

CB Avalanche CenterAvi-Off-Season


 Extra Caution
This past week’s never-ending storm cycles has renewed the promise of a deep and snowy winter in the Elk Mountains. Hopefully, most skiers and riders got to surf their powder boards and slake their thirst for the cold smoke. If you were in the backcountry, your endeavors for epic faceshots were likely punctuated with some boot shaking signs of instability in the snowpack. Aside from wondering why you still don’t have real health insurance, your recent experiences might have brought you to ponder the details of the Avalanche Danger Scale. That’s what I did, anyway.
When was the last time that you read the Danger Scale? I mean, reallyread it. I know, it sounds silly. Green is “Go” red is “Go home,” right? As you look deeper it’s a lot more nuanced than that. It may surprise some backcountry enthusiast to know that the forecasters at the Crested Butte Avalanche Center read the Danger Scale almost every morning. There are days when we may spend fifteen minutes mulling over the specifics of a danger rating before issuing a forecast. This might seem like a trivial thing for a forecaster to do rather than performing some kind of crepuscular snow-ritual deep in the mountains. This attests to the importance we place on the danger rating. Which bring us to the point of Considerable Danger.
Starting December 9ththe Crested Butte Avalanche Center saw the most prolonged period of Considerable avalanche danger so far this season. Sure it’s early, but this period lasted well into late December. Backcountry travelers who were out during this time will recognize that conditions during in this period varied greatly. So, why all the Considerable? This is the beauty and flexibility of this danger rating.
First, some basic criteria would say that “dangerous avalanche conditions” exist under a Considerable rating, and “careful snowpack evaluation, cautious route-finding and conservative decision-making” are essential to staying safe. Though there may be some inherent risk to backcountry skiing and riding, it’s not often that it’s “dangerous.” During times of Considerable danger you really have to be on your game.  The conventional way of thinking about Considerable would tell us that “natural avalanches are possible” and “human triggered avalanches are likely.” This isn’t a time for that romantic picnic lunch you’ve been planning in the middle of your favorite avalanche path. We know that during Considerable danger there’s a good chance we’ll see some kind of avalanches. We want to minimize the amount of time that we’re in any avalanche paths to ensure that we’re not caught in any of them. This is where things get interesting. According to the size and distribution definition, during Considerable danger we could see “small avalanches in many areas, large avalanches in specific areas, or very large avalanches in isolated areas.” In case there’s some confusion with the terms, a large avalanche is something you definitely don’t want to be caught in. This could be big enough to break trees or bury a car. Meanwhile, a “small avalanche” could still be big enough to bury a person. “Specific terrain” could be something like east aspects, while “isolated terrain” could be a 40-degree convex slope containing large rocks. The size and distribution helps explain how different types of conditions can fall under Considerable. Additionally, forecasters strive to match the conditions with a danger that best describes it as a whole.  The overall conditions and size and distribution are just as important to consider as whether we expect natural versus human triggered avalanches. Unfortunately, backcountry riders don’t get to choose which flavor of Considerable they want, but the forecaster often emphasizes the most pertinent elements of a given day’s Considerable.  This helps explain why during mid-December we had so many days that were Considerable. Some days we expected human triggered slides and maybe some naturals, but we new they would be small. Other days we didn’t think there would be lots of activity, but we knew anything that ran it could be big. Some days were really heads up with many small avalanches everywhere and a few large slides on specific slopes.
Most important is to recognize that days with Considerable danger are significantly more hazardous than days at Moderate. Forecasters consider the Danger Scale to be exponential, rather than a linear scale. One step up on the Danger scale could mean that you’re 10 times, or even 100 times more likely to trigger an avalanche. There are lots of times when we can get great powder in the backcountry and even shred some pretty steep slopes. It’s critical that we learn to recognize when it isn’t safe and how to modify our terrain choices to not get caught in dangerous conditions.  If you take some time to review the danger scale, you’ll start noticing how much the CBAC forecasters incorporate the definitions into the daily forecast. Like most readers, the CBAC forecasters are excited for a powder-filled winter. We dream of endless fresh tracks, but most importantly we strive to keep our community safe while enjoying the backcountry.