The North Atlantic Oscillation (NAO) is a large-scale alternation of atmospheric masses between the Icelandic Low and Azores High pressure systems. It has a strong effect on European winter climate especially in its positive mode, which manifests itself by above-average precipitation and severe winter storms in the North Atlantic region. In this study, we use the World Wide Lightning Location Network data and investigate properties of lightning which occurred in Northern Europe during a severe winter 2014/2015, when NAO was in its strongest positive mode over the last two decades. We found that the diurnal distribution of winter lightning was nearly random, nevertheless superbolts with energies above one megajoule surprisingly appeared at night and in the morning hours. They were concentrated above the ocean close to the western coastal areas. We show for the first time that winter lightning in the North Atlantic, including superbolts, were predominantly single stroke flashes.