The EAWS matrix, a decision support tool to determine the regional avalanche danger level (Part A): conceptual development

Abstract

Avalanche forecasting is central to managing risk in snow-covered mountain regions. Standards for regional avalanche forecasting were initially developed at national levels. The introduction of the five-level European Avalanche Danger Scale (EADS) in 1993, still in use today, marked a milestone in harmonizing the assessment and communication of avalanche danger. Since then, both forecasting concepts and terminology have evolved. In this study, we present the updated European Avalanche Warning Services (EAWS) Matrix - a consensus-based decision-support tool developed to support consistent and transparent danger level assessments across Europe. The Matrix links three key factors - snowpack stability, its frequency, and avalanche size - to the five danger levels of the EADS. We describe the participatory development process involving avalanche forecasters from across Europe, including expert surveys and operational testing over three winters. The updated Matrix reflects current best practices in regional avalanche forecasting in Europe and complements the Conceptual Model of Avalanche Hazard (CMAH), while avoiding ambiguous likelihood terminology. Its design aligns with the operational forecasting workflow and explicitly addresses inherent uncertainties. We highlight key findings, such as persistent challenges in reliably assessing the factor classes, uncertainty in danger level assignment around certain transition zones, and the need for clearer definitions and better data. Finally, we argue that the Matrix, now adopted as an EAWS standard, provides a robust foundation for future revisions of the European Avalanche Danger Scale.