The EAWS Matrix is a tool introduced by the European Avalanche Warning Services for determining avalanche danger levels and is based on the definitions of the five-levelled avalanche danger level scale.
The EAWS matrix covers the three important parameters within the definition of the European avalanche danger scale: the probability of avalanche release, the distribution of hazardous sites and avalanche size and occurrence. The EAWS Matrix can be divided into two parts: On the left part of the matrix, the avalanche danger level depends on the distribution of the hazardous sites, the additional load required for avalanche release and the size of the expected avalanches. On the right part, the danger levels are related to spontaneous avalanche activity. The combination leading to the highest danger level is decisive.
The matrix on its y-axis describes the extent of the hazardous sites using the terms “isolated”, “some”, “many” or “many/most”. It is also considered whether these spatially distributed hazardous sites can still be well indicates and communicated in the avalanche forecast, or whether the dangerous terrain may occur so frequently and diffusely that it can no longer be indicated.
On the x-axis, the matrix describes the probability of avalanche release. The artificial and the spontaneous avalanche release is considered in two submatrices. The left matrix refers to the artificial release probability and describes it with the additional load and adverbs or verbs, which gives the probability a paraphrase. The classes range from “General only with high additional load”, “especially with high additional load”, “possible with low additional load” to “likely with low additional load”. These terms express an increase in probability. Since it is not in the nature of man to be able to estimate probabilities well, the matrix tries to provide an estimate for these by means of these different descriptions. The right part of the matrix then describes the spontaneous, i.e. natural, avalanche release via the distribution, number and size of the avalanches to be expected.