EAWS decisions on avalanche problems, hazard level matrix and avalanche sizes

The European avalanche warning services together form the EAWS (European Avalanche Warning Services), a cross-national organization that strives for the most uniform avalanche situation reports possible in Europe. This involves standardized methods in avalanche warning on the one hand and standardized definitions and terminology on the other. Probably the best-known and most fundamental product produced by the EAWS is the five-stage danger level scale, which is defined uniformly throughout Europe.

The most recent conference of the EAWS in summer 2017, the following innovations were decided:

Integration of the 5 avalanche problems into the LLBs

The avalanche problems (fresh snow, drifting snow, old snow, wet snow, sliding snow) are to be increasingly used in all European bulletins and now have standardized definitions and icons. The definitions and graphics developed by the Tyrolean Avalanche Warning Service have largely been adopted. The avalanche problems serve to describe typical situations in more detail and are intended to support avalanche warning officers and winter sports enthusiasts in assessing the situation. The avalanche problems provide supplementary information in addition to the danger level and the description of the danger points and contain general information on the types of avalanches to be expected depending on the problem, the characteristic spatial distribution and the location of the weak layer in the snowpack, as well as typical trigger mechanisms and the duration of the hazard.

Here is a detailed definition of the avalanche problems as a pdf.

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Update of the hazard level matrix

The matrix for determining the hazard level, previously known as the "Bayern Matrix", has been renamed the "EAWS Matrix" and expanded to include the expected avalanche size. The Bayern Matrix was introduced in 2005 and is used to determine the hazard level as uniformly as possible depending on the situation.

The left half of the matrix relates the number or distribution of hazard points to the additional load required for triggering. The right half deals with the danger points and possible self-triggering. Level 3, for example, corresponds to "danger spots in many steep slopes", triggering "already possible with low additional avalanche load" or "self-triggering of size 3, occasionally also size 4 avalanches possible".

The contents of the matrix remain basically unchanged, but the left-hand side has been expanded to take into account not only the additional load, but also the expected avalanche size (small boxes). For example, "danger spots on some steep slopes" in combination with triggering "possible with low additional load" now corresponds to level 1 for expected avalanche size 1, level 2 for size 2 and level 3 for size 3. In the Bavaria Matrix, this combination always means level 3 regardless of the avalanche size.

This innovation was decided primarily with regard to its practical relevance for skiers. Many, easily triggered but very small avalanches (such as many loose snow slides after fresh snow) are sometimes significantly less dangerous for skiers than a few avalanches that are difficult to trigger but can become very large (such as a persistent old snow problem). With the new matrix, this can now be better taken into account in the hazard level assessment.

Colorless fields in the matrix represent situations that are either very unlikely or only occur in certain mountain regions. The combination "isolated danger spots", triggering "only with large additional load" and avalanche size 4 does not usually occur in the Alps. In Norway, on the other hand, cornice breaks (large additional load) occasionally trigger avalanches of size 4 even in otherwise favorable situations (few danger spots).

New names for the avalanche sizes from 2018/19

The EAWS defines 5 avalanche sizes. While the definitions themselves will not change, the names will be changed from the 2018/19 season to better reflect common usage. Size 1, previously "slide", will become "small avalanche". Size 2, the typical skier avalanche, previously "small avalanche", will become "medium avalanche". Size 3, previously a "medium avalanche", becomes a "large avalanche". Size 4, previously a "large avalanche", becomes a "very large avalanche". Size 5, previously a "very large avalanche", becomes an "extreme avalanche".

The purpose of these changes is to improve the description of avalanche sizes 1 and 2 in particular from a skier's perspective. Skiers are mainly injured in size 2 avalanches. Size 2 avalanches typically reach the foot of the slope and are around 50 to 200m long. In general, these avalanches do not appear "small" and are not referred to as "small" in normal usage. The changes will not be introduced until 2018/19 to give the individual LWDs time to adapt their systems accordingly.

A precise definition of avalanche sizes with example photos can be found in the EAWS glossary under the keyword "avalanche size".