Variability of spring temperature extremes in Europe

Spring in particular can carry impact-relevant extreme events over Europe, such as late frost or early summer heat. However, the dominating mechanisms and drivers of such temperature extremes in European springtime are currently not well understood. Across all seasons, one mechanism relevant for temperature extremes in Europe is atmospheric blocking. Unlike winter, where blocking is predominantly related to cold spells, and summer, where blocking is predominantly related to warm spells, spring is a transition period during which both cold and warm spells might be connected to blockings.

While this transition has been statistically analyzed before, available time series were limited, as was, in turn, the spatial analysis. Here, using ERA-5 and E-OBS for the period 1950-2023, with more than doubling the time series, we confirm existing literature on the statistics and the change of blocking patterns throughout the spring season, although our work indicates more early spring warm spells than previously found. The greater data availability also allows the spatial division into blocking regions, allows us to characterize the sensitivity of warm spell frequency to blocking location. We show that blockings over Scandinavia and the UK lead to Northern European warm spells. Comparing springtime occurrences of blocked and unblocked warm spell days shows that in Northern Europe, warm spells often occur simultaneously with blocking, whereas in Southern Europe, warm spells less frequently occur simultaneously with blocking. We identify temporal clusters of preferred occurrences of blocked or unblocked warm spell occurrences in Northern and Southern Europe to trace their seasonal drivers, thus indicating the potential for seasonal predictions of spring warm spells over Europe.