An analysis of trends in large-scale weather patterns (“Großwetterlagen”) associated with ‘Dunkelflaute’ events.

Episodes with low energy generation from wind and solar power have been repeatedly addressed by the German public under the term ‘Dunkelflaute’ (‘dark doldrums’). Previous studies of DWD (Drücke et al.; 2021) have shown that the risk of a shortfall event (esp. in wind energy production in winter) is often related to a specific large-scale weather pattern, the “High over Central Europe”.  When this pattern occurs (with below-average wind speeds in Germany), above-average wind speeds typically occur in other parts of Europe, especially in parts of Scandinavia. This was also the case for the ‘Dunkelflaute’ events observed in Novermber and December 2024.

This pattern is part of an approach of DWD applied for the classification of weather patterns, the so-called “Großwetterlagen” (GWL). The numerical method for automatic classification of 29 GWLs is based on the fields of geopotential height in 500 hPa, relative geopotential thickness (500-1000 hPa) and air pressure at sea level on a regular grid as input data. It is therefore possible to apply the method to reanalysis datasets and thus provide a catalogue of circulation patterns for historical periods. The most recent version of the catalogue with daily classification is called ‘GWL-REA’ (automatic GrossWetterLagen classifier for REAnalysis datasets). It covers the period from 1950 until today. The datasets therefore also allows to analyse trends in the frequency or durartion of relevant events. Trends for the ‘High over Central Europe’ in the winter half-year (October to March) for the period since winter 1950/51 have been analysed, but no increase in the total number of days or in the total number of days was found.