In April 1993, the European Avalanche Services agreed to the use of a uniform scale with five avalanche danger ratings. Until then, countries had used different scales with varying danger ratings (e.g. 8 levels in Catalonia and France, 7 levels in Switzerland, and so on) and with differing definitions for each degree of danger.
The adoption of a uniform scale is extremely beneficial for all snow users, professional and amateur, because we can refer to the same danger ratings when we visit other countries. The United States and Canada use the North American Avalanche Danger Scale, which also includes five danger ratings and whose definitions of each level, though not an exact match, refer to the same as the European scale (www.avalanche.org).
European Avalanche Danger Scale
(*) The avalanche-prone locations are described in greater detail in the Avalanche Advisory (altitude, slope aspect, type of terrain)
(**) Additional loads:
-low: individual skier / snowboarder, riding softly, not falling; snowshoer; group with good spacing (minimum 10m) keeping distances
-high: two or more skiers / snowboarders etc. without good spacing (or without intervals); snowmachine; explosives; single hiker/climber
In an effort to make the information as accurate as possible, the European Avalanche Warning Services provide definitions of the most commonly used terminology. Some of the definitions are briefly explained in the legend accompanying the scale, and they are also included in a glossary available at the EAWS website.
This section of the web intends to be a tool to help understand the avalanche danger rating published in the bulletin. That is, it explains what the rating means and how we can apply it when choosing the terrain for our activities and the group with which we will carry them out.
Danger for each danger level: 4 important points about this scale
1- The scale is not linear. These images from the Swiss website White Risk, show typical size and distribution of avalanches during the various danger ratings.
Your risk increases about two fold for each rising level on the danger scale. In other words, you take on twice as much risk at Moderate as Low and you take on four times more risk going from Low to Considerable. And so on. The risk numbers in the graph below come from Werner Munter’s estimates based on avalanche activity in Switzerland.
2- Most avalanche fatalities occur at CONSIDERABLE (3) danger because the maximum interaction between people and avalanches occurs there. There is also more uncertainty associated with Considerable danger and the difference between dangerous (unstable snowpack) and not-so-dangerous (more stable snowpack) terrain is much harder to identify. Below you can see the statistics of fatal accidents by avalanche in Catalonia in the last 20 years. The numbers are similar in most countries in Europe and North America.
3- The AvaluatorTM is a decision making aid which combines danger rating with terrain classification (ATES). The result is a set of recommendations that adjusts to each person’s training and experience in avalanche terrain. If you fall in the Caution zone (green area of the Avaluator) it is possible to find safe terrain to go to even in days when the danger rating is High (typically simple terrain with gentle slopes and not locally connected to steep slopes).
4 – And finally…some common sense advice
Extreme, catastrophic situation. It is an exceptional situation that does not happen every winter. Large natural avalanches are very likely to occur. Avoid all avalanche terrain.
Very unfavorable conditions. Highest danger for winter activities. It lasts a few hours. Stick to simple and familiar terrain.
Unfavorable conditions. Critical situation. It takes experience and knowledge to move safely around the mountain. More than half of the accidents occur within this danger rating. It is quite frequent.
Mostly favorable conditions. The danger is very localized. This situation tends to be underestimated: don’t drop your guard!. It is the most common danger rating in a normal season. Use prudence.
Favorable conditions. Almost any activity can be undertaken with no restrictions. Stick strictly to good habits on avalanche terrain.