Why The Danger Scale Is Not A Straight Line

The avalanche danger scale looks like a five-point ranking where each step is one unit worse. The relationship between those steps and actual hazard is nothing like that.

The steps grow rapidly

Each level up the scale represents a substantial multiplication of hazard rather than an increment, in both the likelihood of triggering and the size of what results.

Treating a move from the second level to the third as a modest change badly understates it. The terrain that becomes unmanageable at that point is extensive.

This is why bulletins pair the number with a written description, which conveys the change in a way the numeral does not.

The middle of the scale kills

Accident records consistently show that most fatalities occur at moderate and considerable ratings rather than at the top of the scale.

At the highest levels, conditions are visibly bad and most people stay out of avalanche terrain. Very few are exposed, so very few are caught.

At moderate levels, the conditions look fine, the skiing is good and a large number of people are out. The hazard is real, localised and easy to underestimate.

The rating describes a region, not a slope

A forecast covers an area that may span many valleys and thousands of metres of elevation, and it describes the general picture within it.

Individual slopes vary enormously inside that area according to aspect, elevation, wind loading and what happened to that particular piece of ground last week.

A rating is therefore a starting assumption to be tested against what a party actually observes, not a verdict on the slope in front of them.

The problem type carries the detail

Modern bulletins identify specific avalanche problems, describing where they sit, how large a result would be and how likely a person is to trigger one.

These problems behave differently. A wind slab is often obvious and localised, while a persistent weak layer can be triggered from an unexpected place and produce a very large avalanche.

Reading only the number discards this, which is the most common misuse of a bulletin and the one that puts competent parties on the wrong slopes.

How the levels are meant to be used

Each level comes with travel advice describing which terrain the forecaster considers appropriate, expressed in terms of steepness and exposure rather than named runs.

Using the scale properly means letting it constrain terrain choice before leaving, not evaluating a slope after arriving at its base.

Interpreting bulletins is taught on recognised avalanche courses, and the regional forecast centre is the authority for the area you are in on the day you are there.