Thunderstorm Climate of Finland 1998-2007

The ten-year period 1998-2007 of relatively even-quality lightning location data in Finland is summarized into diagrams of spatial and temporal variations. The mean flash density of 0.34 per square kilometre and year is lower than the estimated longest-term, 48-year average of 0.39 available so far, but no clear trends can be drawn. The spatial flash-density distribution varies widely from year to year, but on the average it is concentrated in the central part. Pre-analyzed synoptic weather maps have been used to classify thunderstorms into four frontal and three air mass types, as well as into western (maritime) and eastern (continental) types. Eastern air-mass thunderstorms are the dominant type, both by frequency and intensity, in the most active month July and partly already in June. Otherwise the most frequent type is western frontal, with lower intensity.