Notification of avalanche hazard should not be used as a reason for skiing in potentially avalanche prone terrain, ie terrain steeper than 30 degrees. Examine the conditions, obtain necessary information about snow conditions and terrain, and choose your trip according to the conditions and your skills. The danger is weak layers in the snow-pack. Some years the conditions are more unstable than others. This year it is relatively unstable in Norway, in general.
A combination of factors
Accidents occur because many people are out skiing, often in avalanche prone terrain, with varying local avalanche hazard and unstable layers in the snow-pack. An avalanche expert is almost a detective in the Easter Crime Drama, who collects information and evidence related to the stability of the snow-pack to grade the avalanche hazard. Important tools for avalanche alerting are accurate topographical maps and information from local people.
In order for the avalanche expert to be able to say something about the avalanche hazard, he or she must obtain relevant information. Only by examining the different conditions, the probability for avalanches can be evaluated. Snow is not homogeneous, and one can experience large variations even at shorter distances. Therefore, it may be appropriate to investigate the snow's stability and layering at several different locations, and not only examine one location.
If an avalanche has already occurred, the expert must evaluate the risk of moving within the avalanche area. This can lead to challenges related to the assessment of snow layers. If it is dangerous to move within the avalanche area, it will at the same time be difficult to say anything about the snow layering and stability. In such cases, helicopters can be used to observe avalanche activity over larger areas, and also to access and investigate possible release areas safely.
The slope of the terrain is an important factor for the release of avalanches. From the terrain slope and snow cover, one can say something about the likelihood of avalanches and where it will be released. Often, avalanches can occur as a result of an increased load that the snow cover cannot withstand, for example by skiers or weather conditions such as heavy snowfall, wind or rain.
Snow avalanche usually occurs in terrain steeper than 30°, but this alone is not an absolute indication factor for potential avalanche risk. Remember that avalanche terrain also include areas that can be reached by landslides that can be released above you. Mountain sides lying in lee are most prone to avalanches. On this side the snow is collected when transported by the wind. In these areas, often in the shelter of a mountain ridge, there is more snow than in surrounding terrain.
The avalanche hazard is graded on a scale with a degree of danger from 1 to 5, which constitutes very high probability of avalanches. The scale describing the degree of danger is common throughout Europe. For example, the definition states that at degree 4, "snowpack is poorly bonded in most steep slopes" and "triggering is likely even from low additional loads on many slopes".
Experience and up-to-date information
Although all surveys have been done according to the book, one can still make mistakes. Historical events can give indications of what to expect from different conditions. Equally important is the experience and understanding of all the coinciding causes that can eventually end up with an avalanche.
Avalanche hazard evaluations are "fresh commodity", and conditions can change quickly. Fieldwork provides important information about the current conditions. The weather for the next few hours and days can change conditions dramatically. In such cases it's back to square one! For those who want to go skiing in the mountains, the following rule of thumb applies: Avoid landslide terrain. Have a happy Easter in the mountains!