How Is Avalanche Forecasting Done?

An avalanche forecaster understands the stability of the snowpack, then determines what it would take for a particular area of snow to become unstable, resulting in an avalanche. Picture the snowpack as a balancing scale. On one side of the scale there is conditional stability, the other scale has weight. When the density of the snow, or added weight of a victim rises above the amount of stability, the scale tips and boom, an avalanche occurs.

The slides which capture climbers, snowmobilers, and snowboarders are usually triggered by their own weight, but the potential of an avalanche is evaluated by looking at the weaknesses in the snow layers and the characteristics of each slope. After years of collecting numerous types of data and analyzing accident sites, several tests have been developed which reveal instability. Using these tests and a good dose of experience, forecasters can tell you when a slide is likely to occur. Avalanche control work can be found at ski areas, on state highway programs, and in the Forest Service as snow rangers. Helicopter, snowcat operations and backcountry guiding services also hire avalanche forecasters who have advanced first aid skills.

A forecaster evaluates the snowpack, the terrain and the weather. Since all these variables can combine to form numerous combinations, it is difficult to develop a set model to show instability or set up a mathematical equation to tell exactly when an avalanche will occur. Instead it takes many years of learning from the mountains and experienced peers. Rod Newcomb from the American Avalanche Institute explains that “The books will teach you the rules, but Mother Nature will teach you the exceptions!” Using information about an area gained throughout several winter seasons, veteran forecasters appear to develop a sixth sense about the danger. They will often rely on their instincts just as much as their tests.

Terrain factors of slope orientation, steepness and roughness are fixed. On the other hand the weather and snowpack change constantly. Factors that influence the snow layers are: temperature, wind, and precipitation. Basically a forecaster takes in all this data throughout the winter. Their interest is in knowing how one storm bonds to the next and if layers in the snowpack are becoming weaker or stronger.

Snow depth, snow surface, and settlement, are all pieces of the forecasters puzzle? How many inches of snow fell? Everyone likes to ask that one. Which direction did the wind blow and how hard? What was the temperature? Many times the answers to these questions can vary from the beginning to the end of a storm, as well as from one side of the mountain to the other and with regard to elevation. These factors are all important, since they affect the structure of the snow crystal itself. In general, the crystal can make snow bond together, develop a thick wind slab, produce a weak layer or make a good slide plane for future storms.

Having professional forecasters out there performing stability tests and making public statements about the level of danger has allowed us to explore within a ski area boundary without considering the danger. Now as snowboarders become more and more inclined to seek out untracked turns in the backcountry, each individual must rely on their own judgement. Because each area has distinct differences and since variables change so rapidly, it is essential backcountry users become self sufficient.

So, whether you are interested in becoming a professional forecaster or you’re interested for personal enjoyment, take a class and learn from experienced people around you. After taking a level one course at Peak Adventures, a fity- five-year-old was reminising about many dangerous experiences he had been in. Excited about his new insight of avalanche awareness he said “I’ll never look at snow the same again!”