Extreme storm track seasons and their influence on wind and precipitation extremes

Extratropical cyclones are important modulators of extreme weather in the midlatitudes, with impacts ranging from sub-hourly to seasonal time scales. On seasonal time scales, the aggregation of cyclones in specific regions can lead to anomalous storm track configurations, inducing a seasonal clustering of surface weather extremes with significant societal impacts. Notable examples include the southward shifted storm track associated with the exceptionally negative North Atlantic Oscillation during winter 2009/2010 and the exceptionally stormy winter of 2013/2014 over the British Isles and Ireland. While the role of anomalous storm tracks is often discussed in case studies of extreme seasons, a systematic identification and characterization of extreme seasonal configurations of the extratropical storm tracks is lacking.

We use eddy kinetic energy at 850 hPa to identify anomalous extratropical storm track seasons – referred to as storm track extremes – in the ERA5 reanalysis and explore their characteristics. Using a cyclone-tracking algorithm, we show that storm track extremes are generally induced by both changes in regional cyclone frequency and shifts in the mean intensity of these cyclones. We then assess the role of the El Niño–Southern Oscillation (ENSO) by examining the occurrence of storm track extremes across different ENSO phases and regions. Finally, we investigate how seasonal storm track extremes are linked to surface weather by assessing the frequency of daily precipitation and wind extremes during extreme storm track seasons and how they are related to individual extratropical cyclones. Our work presents the first systematic identification of anomalous storm track seasons and a multi-scale analysis of cyclone-related extremes, highlighting the role of cyclones in shaping seasonal variability and anomalous configurations of storm tracks.