SummaryAs wind and solar power provide a growing share of Europe’s electricity1, understanding and accommodating their variability on multiple timescales remains a critical problem. On weekly timescales, variability is related to long-lasting weather conditions, called weather regimes2–5, which can cause lulls with a loss of wind power across neighbouring countries6. Here we show that weather regimes provide a meteorological explanation for multi-day fluctuations in Europe’s wind power and can help guide new deployment pathways which minimise this variability. Mean generation during different regimes currently ranges from 22 GW to 44 GW and is expected to triple by 2030 with current planning strategies. However, balancing future wind capacity across regions with contrasting inter-regime behaviour – specifically deploying in the Balkans instead of the North Sea – would almost eliminate these output variations, maintain mean generation, and increase fleet-wide minimum output. Solar photovoltaics could balance low-wind regimes locally, but only by expanding current capacity tenfold. New deployment strategies based on an understanding of continent-scale wind patterns and pan-European collaboration could enable a high share of wind energy whilst minimising the negative impacts of output variability.

Extreme states of the stratospheric polar vortex can have long‐lasting impacts on extratropical circulation patterns, such as the North Atlantic Oscillation (NAO). This provides windows of subseasonal predictability beyond the typical weather forecast horizon of about 10 days. Subseasonal forecasts of surface weather are of significant interest in weather‐dependent socio‐economic sectors. For example, demand and supply for electricity and gas are weather dependent and therefore accurate forecasts are important for the energy industry and energy trading. Here we investigate the subseasonal impact of stratospheric conditions on surface weather events relevant to the energy industry in five subregions of Europe in winter. We use a definition of seven Atlantic–European weather regimes to describe the variability of the large‐scale circulation on subseasonal time scales. Results indicate that weather events are often associated with more than one preferred weather regime. In turn, some weather regimes project onto a specific NAO phase, while others are independent of the NAO. As expected, anomalous stratospheric polar vortex states predominantly modulate the occurrence of regimes related to the NAO and affect the likelihood of their associated weather events. In contrast, the occurrence of weather regimes which do not project well onto the NAO is not affected by anomalous stratospheric polar vortex states. These regimes provide pathways to unexpected weather events in extreme stratospheric polar vortex states. For example, weak stratospheric polar vortex states enhance the likelihood of negative NAO. High wind events in Central Europe predominantly occur during the zonal regime, strongly projecting onto positive NAO. However, these events also occur during the Atlantic trough regime, which is unaffected by anomalous stratospheric polar vortex states and thus provides a pathway to Central European high wind events during weak stratospheric polar vortex states. A correct NAO prediction alone is therefore not sufficient to correctly predict surface weather after extreme stratospheric polar vortex states. Moreover, weather regime life cycles independent of the NAO also need to be forecast accurately.

Wind power is playing an increasingly important role in Europe's electricity generation. Accurate forecasts of wind‐power output on various spatial and temporal scales are therefore of high interest for the energy industry. However, predictability of near‐surface wind on subseasonal time‐scales has received relatively little attention. The stratosphere is an important source of subseasonal predictability in winter. Here, we study the implications of the lower stratospheric circulation for month‐ahead wind electricity generation in Europe in winter. Using ERA‐Interim reanalysis and the novel wind‐power dataset Renewables.ninja, we demonstrate a strong relationship between the lower stratospheric circulation and month‐ahead wind electricity generation in different parts of Europe in the period 1985–2014. This relationship exists due to episodes of troposphere–stratosphere coupling, which lead to prolonged periods of either the positive or negative phase of the North Atlantic Oscillation (NAO). Since these persistent NAO periods are associated with strong surface wind anomalies, they have an important impact on wind electricity generation, in particular in Northern Europe. The state of the lower stratospheric circulation also determines the exact latitudinal position of these prolonged NAO patterns, with contrasting implications for wind electricity generation in specific countries. Using simple statistical forecasts, we show that the observed relationship between the lower stratosphere and wind electricity generation can be used for skilful forecasts of month‐ahead wind electricity generation. Particularly high forecast skill is found when the circulation in the lower stratosphere differs strongly from its climatological mean. Anomalous states of the lower stratospheric circulation therefore provide windows of subseasonal‐range predictability for wind‐power output in many European countries.

Meteorologists in the energy industry increasingly draw upon the potential for enhanced sub-seasonal predictability of European surface weather following anomalous states of the winter stratospheric polar vortex (SPV). How the link between the SPV and the large-scale tropospheric flow translates into forecast skill for surface weather in individual countries-a spatial scale that is particularly relevant for the energy industry-remains an open question. Here we quantify the effect of anomalously strong and weak SPV states at forecast initial time on the probabilistic extended-range reforecast skill of the European Centre for Medium-Range Weather Forecasts (ECMWF) in predicting countryand month-ahead-averaged anomalies of 2 m temperature, 10 m wind speed, and precipitation. After anomalous SPV states, specific surface weather anomalies emerge, which resemble the opposing phases of the North Atlantic Oscillation. We find that forecast skill is, to first order, only enhanced for countries that are entirely affected by these anomalies. However, the model has a flow-dependent bias for 2 m temperature (T2M): it predicts the warm conditions in Western, Central and Southern Europe following strong SPV states well, but is overconfident with respect to the warm anomaly in Scandinavia. Vice versa, it predicts the cold anomaly in Scandinavia following weak SPV states well, but struggles to capture the strongly varying extent of the cold air masses into Central and Southern Europe. This tends to reduce skill (in some cases significantly) for Scandinavian countries following strong SPV states, and most pronounced, for many Central, Southern European, and Balkan countries following weak SPV states. As most of the weak SPV states are associated with sudden stratospheric warmings (SSWs), our study thus advices particular caution when interpreting sub-seasonal regional T2M forecasts following SSWs. In contrast, it suggests that the model benefits from enhanced predictability for a considerable part of Europe following strong SPV states.