The most severe thunderstorm this year in Finland pounded Helsinki and several other cities in South-Finland. The strong mesoscale convective system had lightning intensities over 4000 strikes in an hour. The Finnish Meteorological Institute issued a rare warning advising people to stay indoors. About 40 000 households were left without power, traffic lights stopped working, trains were stalled and at least one person was hit by lightning. These are a few screencaps from a video I shot. Because the storm was elevated over a cloud layer one could not see it coming beforehand as there was no arcus cloud visible.