Abstract
Abstract. In the European Alps, the public is provided with regional avalanche forecasts, issued by about 30 forecast centers throughout the winter, covering a spatially contiguous area. A key element in these forecasts is the communication of avalanche danger according to the five-level, ordinal European Avalanche Danger Scale (EADS). Consistency in the application of the avalanche danger levels by the individual forecast centers is essential to avoid misunderstandings or misinterpretations by users, particularly those utilizing bulletins issued by different forecast centers. As the quality of avalanche forecasts is difficult to verify, due to the categorical nature of the EADS, we investigated forecast goodness by focusing on spatial consistency and bias, exploring real forecast danger levels from four winter seasons (477 forecast days). We describe the operational constraints associated with the production and communication of the avalanche bulletins, and we propose a methodology to quantitatively explore spatial consistency and bias. We note that the forecast danger level agreed significantly less often when compared across national and forecast center boundaries (about 60 %) than within forecast center boundaries (about 90 %). Furthermore, several forecast centers showed significant systematic differences in terms of more frequently using lower (or higher) danger levels than their neighbors. Discrepancies seemed to be greatest when analyzing the proportion of forecasts with danger level 4 – high and 5 – very high. The size of the warning regions, the smallest geographically clearly specified areas underlying the forecast products, differed considerably between forecast centers. Region size also had a significant impact on all summary statistics and is a key parameter influencing the issued danger level, but it also limits the communication of spatial variations in the danger level. Operational constraints in the production and communication of avalanche forecasts and variation in the ways the EADS is interpreted locally may contribute to inconsistencies and may be potential sources for misinterpretation by forecast users. All these issues highlight the need to further harmonize the forecast production process and the way avalanche hazard is communicated to increase consistency and hence facilitate cross-border forecast interpretation by traveling users.
Highlights
In the European Alps, public forecasts of avalanche hazard are provided throughout the winter
Even though the forecast products provided by the individual forecast centers may differ in their structure, we assume they adhere to the principles defined by the European Avalanche Warning Services (EAWS, 2017c)
In spring situations, when avalanche hazard often increases with daytime warming, the afternoon rating is higher than the morning one; these two distributions differ significantly (p < 0.01)
Summary
In the European Alps, public forecasts of avalanche hazard are provided throughout the winter. These forecasts – called advisories, warnings, or bulletins1 – provide information about the current and forecast snow and avalanche conditions in a specific region. Avalanche warning services (AWSs) are national, regional, or provincial agencies in charge of providing publicly available forecasts of avalanche hazard (EAWS, 2017c). Even though the forecast products provided by the individual forecast centers may differ in their structure, we assume they adhere to the principles defined by the European Avalanche Warning Services (EAWS, 2017c)
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