Classifying extratropical cyclones and their impact on Finland’s electricity grid: insights from 92 damaging windstorms

This study investigates the impacts of extratropical cyclones on Finland's electricity grids, focusing on 92 significant windstorms from 2005 to 2018. We present a classification method for extratropical cyclones based on the arrival location and direction. Rather than using meteorological criteria to identify windstorms, we select them based on their impacts, namely the number of power outages, to reach a more targeted understanding of windstorm impacts compared to traditional approaches. Key findings indicate that south-west-originating windstorms cause the most damage in total, while north-westerly windstorms individually lead to the highest average outages. The largest impacts occur when a windstorm moves across the northern part of the country, from the north-west to east, with the strongest wind gusts concentrated on the southern side of the low-pressure centre, in highly populated regions. Of the meteorological characteristics of windstorms, the most relevant for grid damage besides the wind gust speed are the extent and spatial distribution of wind gusts. The seasonal analysis shows that windstorms are more frequent and damaging in autumn and winter, but even weaker wind speeds during summer can cause significant damage. Factors such as soil frost influence the severity of windstorm damage, highlighting the importance of expanding research to include environmental and geographical aspects.