Prediction of European Winter 2023/24: Influence of a Strong El Niño

ABSTRACT UK winter 2023/24 had a particularly stormy start, similar to 2015/16, another strong El Niño winter. Successfully predicted by the Met Office seasonal forecast system, this increased early‐winter storminess was associated with lower‐than‐average surface pressure to the west of the UK. Although late winter during El Niño is often associated with the negative phase of the North Atlantic Oscillation (NAO), in 2023/24 the NAO was near‐neutral in observations and weakly positive in the ensemble mean forecast, the late‐winter Atlantic surface pressure pattern in the forecast resembling the response observed during the very strongest El Niño events. Both observations and the forecast showed relatively higher pressure west of the UK, but north‐west Europe and the southern North Atlantic were more cyclonic than forecast. The forecast ensemble mean stratospheric polar vortex (SPV) was relatively strong, and unusually, the mean of ensemble members which had a sudden stratospheric warming (SSW) did not project strongly onto the negative NAO, analysis suggesting tropospheric teleconnections masked the usual SSW impact. Conversely, the observed SPV was weak; however, a mid‐January SSW had little surface impact. Overall, our analysis suggests that, despite some differences in late winter, El Niño was the principal driver of observed conditions in the North Atlantic‐European sector.