September in Lapland unusually warm and dry
The monthly mean temperature ranged from 13 °C Celsius in Åland and the south-western archipelago to slightly under 9 °C in northern Lapland. The biggest deviation from the long-term average was reported in western and northern Lapland, where temperatures were more than 3 degrees above normal levels. The smallest deviation was reported in the southern part of the country were the temperatures were 1 degree warmer than usual. The highest temperature of the month, 23.8 °C, was measured in Sepänkylä, Espoo, on 8 September and the lowest, -6.4 °C, in Vuotso, Sodankylä, on 30 September.
Equally warm September in Lapland last in 1963
Mean temperature was exceptionally high in Lapland, making September 2013 was the warmest in 50 years. According to the statistics of the Finnish Meteorological Institute, the previous time that September in Lapland was a warmer than this year was exactly 50 years ago in 1963.
According to a definition of seasons based on temperature, 'thermal autumn' began in the majority of Lapland on 21 September, which is exceptionally late. As thermal summer began exceptionally early in Lapland, the summer period was exceptionally long and in many areas the longest in 50 years. With the cooling of temperatures at the end of the month, thermal autumn reached the entire country within a few days, attaining the southernmost parts of Finland on 23 September and Åland one day later, which just about matches the long-term average.
Precipitation levels lower than usual
The monthly precipitation levels remained lower than average in the majority of the country, with rainfall levels of less than half of the long-term average recorded in many areas in the western part of the country and Lapland. Precipitation levels were higher than average in large parts of Eastern Finland and Åland and the south-western archipelago. The amount of rainfall in Åland and parts of North Karelia was in excess of 70 mm, whereas in large parts of the Tampere Region and north-western Lapland the rates were under 20 mm. In large parts of Lapland, the autumn was exceptionally dry. A September as dry as this year occurs on average once in ten years.
The heaviest rainfall measured by observation stations was reported at Jomala, Åland, where the monthly precipitation level was 120 mm. The highest 24-hour rainfall level of 42.1 mm was also recorded there on 17 September. The lowest amount of precipitation, 9 mm, was reported at Tottijärvi, Nokia.
Thunderstorms occurred particularly in sea areas, which is typical of thunderstorms at the end of summer. The number of cloud-to-ground lightning strikes, approximately 1,700, remained far below the long-term average for September (4,600). In land areas, the most significant days for thunder were 11 September, when thunderstorms were recorded in Lapland and 12 September when they occurred on the southern coast and in Northern Ostrobothnia.