The annual mean temperatures for 2010 ranged from about 5° C in Southwest Finland to about -3° C in Northern Lapland.
The average precipitation for the whole country was about 560 millimetres, which is about 30 millimetres less than normally. The highest annual precipitation was measured in the area extending from Southwest Finland to Kainuu, where rainfall locally exceeded 650 millimetres. The least rain was measured in Western Lapland, where precipitation was locally under 450 millimetres. When compared against long-term averages, the eastern parts of the country and the west coast received the least rain.
Long cold spells in winter
The year 2010 began with freezing weather. The cold period had begun before the turn of the year. The winter 2009–2010 was the coldest since the winter 1986–1987. The mean temperature for December–February was 3 to 5 degrees lower than the average for the years 1971–2000. The mean winter temperature for the whole of Finland was –12° C, while the long-term average is –8.9° C. The mean winter temperatures ranged from about –7° C in Southern Finland to about –14° C in Lapland. Long periods of subzero temperatures were a characteristic feature of the winter’s weather; in some places, they were among the three longest measured within the past 50 years. The lowest temperature for the winter, and for the whole year, was –41.3° C, measured in Kalliojoki, Kuhmo on 20 February. The previous time when the temperature had dropped below –40° C was in February 2007. Even though precipitation for the winter was less than normally, there was unusually much snow in Southern Finland because virtually all rain fell as snow. For example in Helsinki, the greatest snow depth was 74 centimetres; the previous time when there had been equally much snow was in winter 1969–1970.
Hot weather began in May
The spring, i.e. the period from March to May, was unusually warm. The mean temperature for the whole country was 1.7° C, which is 0.9 degrees higher than normally. Thermal spring began at the end of March in Southern and Central Finland, and even in most parts of Lapland it began in early April. This is customary in Southern Finland but almost a month earlier than normally in Lapland. The most notable feature about the spring weather was the exceptionally early hot spell in mid-May. The highest number of hot days (temperature over 25° C) was recorded in Utti, Kouvola, where they numbered eight. This is the greatest number of hot days recorded at any observation station in May.
The highest temperature during spring was 29.6° C, measured in Kruunupyy on 14 May. In most regions, precipitation in spring exceeded the average. In some places, precipitation was double the normal figures.
Record-high temperatures and storms in summer
The mean temperature for the summer, or the period from June to August, was 14.9° C, which is 1.2 degrees higher than the average for the years 1971-2000. The mean temperature was higher than normally up to Central Lapland, and in Southeast Finland the difference was nearly three degrees. Thermal summer began in Southern Lapland as much as one month earlier than normally.
A particularly warm period occurred in July and early August, when several temperature records were broken. The most remarkable of the records is the new national temperature record of 37.2° C, which was reached at Joensuu Airport in Liperi on 29 July. The previous record, 35.9° C, had been measured in Turku in 1914. Apart from the national temperature record, a new monthly mean temperature record was also made: the mean temperature for July was 23.0° C in Puumala. In addition, a new record was also reached in the number of hot days (temperature over 25° C): in all, 28 hot days were measured in July in Lahti. The 24th of July was the only day when the temperature did not reach 25° C at any observation station in Finland. A new temperature record for August was also made: 33.8° C, measured on 7 August in Heinola and Puumala and on 8 August in Lahti. The previous temperature record for August had been 33.2° C, measured in Sulkava in 1912.
The warm weather was also accompanied by thunder and storms that caused major damage in forests. The worst storms were Asta (29 July), Veera (4 August), Lahja (7 August) and Sylvi (8 August). Of these, Asta caused havoc in an area extending from Southeast Finland to Central Ostrobothnia, whereas Veera, Lahja and Sylvi hit the hardest on Western and Central Finland.
After a long period of unremarkable thunderstorm activity, the number of thunderstorms was greater than normally. The number of ground flashes registered in the whole of Finland was about 170,000, which is about 30,000 more than the long-term average. The most violent thunderstorms occurred in early August. Hail observations between May and September reached a new record, and the strongest hailstorms also took place in early August.
Precipitation was less than half of the long-term average. However, there were wide regional variations in the precipitation figures for the summer. The greatest rainfall within 24 hours for the summer – and the whole year – was 69.5 millimetres, measured in Simpele, Rautjärvi on 4 August.
Cold set in rapidly in November
The mean temperature for autumn, or the period from September to November, was close to normal values throughout Finland. The mean temperature for the whole country was 2.1° C, or the same as the average for the years 1971–2000. The most notable feature in the autumn temperatures was the unusual cold spell that began in mid-November. At the end of the month, coldness records for November were reached in some localities. For instance in Mariehamn, the temperature dropped to –20° C. The previous record for November, –18.5° C, had been measured in 1909. Total precipitation for the autumn was slightly greater than normally in northernmost Lapland and in some areas in Central Finland, whereas in Southern and Central Lapland precipitation was 60–70% of average figures.
The cold spell that started in mid-November continued throughout December. December was colder than normally in the whole of Finland. A remarkable feature in December was the large amount of snow on the south coast and in Kymenlaakso. In the Helsinki area, snow was even exceptionally deep for the time of the year. The snow depth measured in Kaisaniemi, Helsinki on 20 December was 67 cm, or very close to the all-time record snow depth for December, 70 cm, measured in 1915.
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