Hazard Ratings for Powder Pigs

The Avalanche Review, VOL. 6, NO. 4, MARCH 15, 1988
Copyright © All Rights Reserved; AAA

Hazard Ratings for Powder Pigs
according to Bruce Tremper

Last season, there were 23 people in the US that got snuffed by the big guy in the white suit. It's hard to call them "victims" since the vast majority of them triggered the slide which killed them. The statistics also say that most were experienced backcountry skiers and climbers: the more skilled, the better the chances of being killed in an avalanche. As usual, the trouble has come because most of their avalanche skills have not kept up with their skiing or climbing skills.

But never fear. Why waste time digging snowpits and reading avalanche books when you can just call the local avalanche forecast center? That's their job, right?

Here in Utah, 50,000 people per year call our 2-minute avalanche information recording--more than twice as many as any other avalanche center in the country. They are mostly hard-core backcountry skiers looking for any clue that will keep them alive in radical avalanche terrain. What we say and how we say it is literally of life and death importance. I am the director of the Utah Avalanche Forecast Center and I spend a lot of time thinking about these things.

Back in the old days, avalanche forecast centers would simply issue a blanket avalanche hazard rating for a region such as a mountain range, "Today the avalanche hazard is moderate". Then they would recite the standard definition of moderate hazard: "Areas of unstable snow exist and avalanches are possible on steep snow covered slopes and gullies. Backcountry travelers should use caution."

In other words, moderate hazard means that some slopes will slide while others will not. I can almost see the frustrated look on Joe-gnarly, powder pig's face as he's mumbling with the telephone in his ear, "Yah, so what. Which slopes are safe and which ones aren't. Tell me! Last time I call this number." Click.

Yes, the broad-brush approach does have its problems.

First, as any experienced snowpit digger knows, the degree of instability varies considerably not only within different areas of a mountain range but within different areas on the same mountain--and even across a single slope on a particular mountain. Rather, variations in snow stability tend to correlate most closely with aspect, elevation and slope steepness.

Another problem is that most human-triggered avalanches occur during times of moderate hazard. This is because high and extreme hazard seem self-explanatory enough and people tend to stay at home around the fire with a good book. And during times of low hazard, although there's lots of people out, human-triggered avalanches are quite rare. It is the vast middle ground of moderate hazard where the maximum interaction between people and avalanches occur (figure 1). People tend to perceive moderate hazard as being safe enough to ski, yet people without good routefinding and snow stability skills are sure to eventually stumble into one of the localized boobie traps.

Also, moderate hazard is used by forecasters more often than any other category because, let's face it, two thirds of the time, that's how it is out there. "Areas of unstable snow exist and avalanches are possible ...." It sounds like a broken record after awhile.

For these reasons, avalanche forecast centers have begun putting more detail in the forecast, yet still using the old hazard categories to describe that detail. "There is a high hazard above treeline in wind exposed areas mostly on north and west facing slopes steeper than 35 degrees ...." Finally Joe-gnarly has something he can use. However, I keep thinking about ways to build a better mouse trap. There must be a better way, still, to communicate avalanche information.

Here in Utah, with its huge concentrated population of backcountry skiers, its over abundance of steep avalanche terrain and the ridiculously easy access to it, skiers have become pretty cagy about avalanches. For example, about 90 percent of the backcountry skiers carry beacons and shovels and have attended at least some type of avalanche class. Although we notice that some of them use stability evaluation techniques might be better described as avalanche voodoo, they're really a pretty sophisticated lot. We credit this, in part, to the disproportionately low fatality rate in Utah. So we wonder if perhaps they have outgrown their need of avalanche hazard categories altogether.

For example, before I came to Utah I worked for the Alaska Avalanche Forecast Center where we never used avalanche hazard categories. We simply told it like it was. Alaskans seemed comfortable with this, as we enjoyed one of the highest call rates per capita in the country. However, they are an extremely well avalanche educated bunch since most were trained by P" Fredston, Doug Festler and Co. in the renowned, state-funded Alaska Avalanche School (which has since lost its state funding as have most other programs in postbust Alaska but continues as a private, nonprofit school).

Also, here in Utah there seems to be a rising amount of local comments about the inadequecies of hazard ratings. For example, in a recent article, avalanche instructor and guide Dennis Turville, says, "Many people criticize the avalanche report because it tends to say the avalanche hazard is "moderate" most of the time, but this is, unfortunately quite true. I can't say I have a firm understanding of what "moderate "means either, but the important feature of this excellent report is that it tells you what to avoid ....If you think you can make your own slope stability analysis, you're likely fooling yourself, but avoiding slopes which have a higher statistical probability of sliding is something anyone can do and do well."

So what are some other options? The way I see it, no matter how you boil it down, the basic information a person needs to know when traveling in avalanche terrain are:

1. The degree of instability, or the probability of triggering a slide if you skied a certain kind of slope.

2. The distribution pattern of the instability. For example, is it widespread or localized? What aspect, elevation and slope angle? Is it in wind exposed terrain, in sheltered areas, etc?

3. How big will the slide be. For example widespread areas with high probabilities of triggering a 2 inch thick soft slab is a lot different than localized areas with 3 foot deep avalanches.

Avalanche hazard categories are really a way of summing up all three factors into just one word. Is just one word too simplistic, too misleading? Is providing all the details too complicated, too confusing? I'm not sure. To find out, we are presently consulting communication experts, and we hope to test various formats on volunteer subjects to see which most effectively communicates avalanche information.

One format we are looking into is using probabilities of human triggered releases. For example, "Today we feel there is a 5-15 percent probability of human triggered releases on north and east facing slopes above 9,000' steeper than 35 degrees ...." When I was in Europe last summer, I was interested to hear that the Europeans would love to use probabilities in their forecasts but they felt that most Europeans did not sufficiently understand the concept. They were excited to find out that in the United States the National Weather Service had been using probabilities of precipitation for many years and have had very good luck with it.

So what is the perfect avalanche forecast format? Well, I'm not sure. But I do know that it must be both obvious enough for avalanche neophites to understand, yet give enough useful detail for the hard-core skiers to make routefinding decisions. That's a tough bill to fill. No, the perfect avalanche advisory certainly hasn't been invented yet, but we're working on it.