Summer

In summer, the mean daily temperature is consistently above 10°C. Summer usually begins in late May in southern Finland and lasts until mid-September. Summer in Lapland starts about one month later and ends a month earlier than the south coast. The regions north of the Arctic Circle are characterized by 'polar days', when the sun does not set at all. The northernmost parts of Finland have 73 such days every year. Even in southern Finland, the longest day (around Midsummer) is nearly 19 hours long. The warmest day of the year comes about one month after aphelion, i.e. around July 20, in the whole of Finland. The highest summer temperatures in the Finnish interior are from 32°C to 35°C.

Near the sea and in the islands, temperatures over 30°C are extremely rare; the highest temperature ever recorded in Helsinki is 31.6°C. The highest temperature ever recorded is from July 9, 1914, when 35°C was exceeded in several places (the maximum being 35.9°C in Turku). Heat waves, with a maximum daily temperature exceeding 25°C, occur on an average of 10 to 15 days per summer inland in southern and central Finland, and 5 to 10 days in northern Finland and on the coast. In the course of the summer, thunderstorms occur on 8 to 14 days in the interior and 4 to 8 days on the coast and in northern Lapland.