Press release archive: 2005

Weather in Finland 2004: Heavy rain and intense weather phenomena

24.3.2005 12:00

The exceptionally heavy rains at the end of July and at the beginning of August were the most prominent feature of the weather in 2004. The annual precipitation was high everywhere in Finland. April was the only month when there was little precipitation.

Precipitation was generally 600-900 millimetres in 2004. Only April was a dry month in the whole of Finland. Even in Lapland, local precipitation figures were over 700 millimetres, which is exceptional for the area. In areas with much rainfall, the annual precipitation exceeded the average by 100-200 millimetres.

The area with the heaviest rains during the last week in July extended from the southern parts of Kainuu through Northern Savo and Lake Päijänne to Central Uusimaa and the Helsinki area. The greatest daily precipitation, 122 mm, was measured in Vesanto on 28 July. Torrential rains raised water levels in lakes considerably, and rivers in Uusimaa were close to their flood peaks. The earlier precipitation records for July were exceeded at several sites. The highest rainfall figures for the month were 200-246 mm. On 3 August in Oravainen, Ostrobothnia, 151 mm of rain was measured within a seven-hour period. Major flood damage occurred, for instance, in the municipalities of Vöyri, Oravainen and Lapua.

In 2004 the annual precipitation in extensive areas ranged between 600 and 900 mm, or was generally 1.2-1.3 times the longterm average. Precipitation was also exceptionally high in Lapland, in places exceeding 700 mm. The greatest annual precipitation, 1009 mm, was measured in Kivivaara, Lieksa, located in the hilly region of Northern Karelia. However, the greatest precipitation in 2004 still fell short of Finland's all-time record of 1109 mm, which was measured in Nupuri, Espoo in 1981.

A year slightly warmer than average
Despite the rainy summer - and owing to the mild December - the annual mean temperature was slightly above average everywhere in Finland. The mean temperature for the whole year was about half a degree higher than the average in southern and eastern parts of the country and about one degree higher than the average in Ostrobothnia and in Lapland. The highest temperature for the year, 29.8° C, was measured in Sevettijärvi, Inari on 3 July, while the lowest temperature, -38.7° C, was measured in Naruska, Salla on 11 February.

The hot weather of early May in southern and central Finland, and the spell of ten hot days in Lapland in July, were both exceptional cases. Otherwise the number of days when the afternoon temperature rose above 25° C was lower than usually.

The end of the year was very mild. The mean temperature in December was about three degrees, and in the Province of Lapland even 4-6 degrees, higher than normally.

Night frosts and heavy rains disrupted the growing season
The thermal growing season, i.e. when the daily mean temperature stays above five degrees, began as early as mid-April in the southwestern and western parts of the country. The exceptionally warm weather in early May accelerated growth to a record speed. However, cold air arriving from the north brought the growing season to a complete halt on 11 May. Night frosts occurred in both May and June. For example, in Orimattila the most severe night frost temperature, -9.8° C, was measured on 13 May. After rapid growth, plants suffered badly from these severe frosts. Following this period the next night frosts did not occur until after mid-August.

Precipitation during the thermal growing season was as much as 150-200 mm above average in Uusimaa, Häme, the Oulu Province, and in the municipality of Enontekiö in Lapland.

A summer with a normal lightning frequency
During the summer, a total of 140,000 lightning strokes occurred within the territory of Finland; this is slightly below the long-term average. The highest daily lightning frequency was measured in the northernmost Lapland. The highest number of lightning strokes occurred between the beginning of July and the end of August.

In summer 2004, over 15 trombs were recorded in various parts of the country in connection with thunderstorms. The strongest of these was the tromb that traveled through Kontiolahti on 20 August, causing serious damage to property. The previous equally harmful tromb in Finland had crossed the outskirts of the town of Mikkeli in June 1998.

Few wind storms during the year
Wind storms occurred in our sea areas only in January and March and again in November and December. A wind storm regarded as significant on the basis of wind speeds took place on 2 and 3 March in the western sea areas. The highest mean wind speed then recorded over a period of ten minutes was 29 metres/second, measured in Valassaari in the Gulf of Bothnia. There were five stormy days in November and four in December. Rafael, the wind storm that began on 22 December, was the most extensive wind storm in 2004. On 23 December, the speed of southerly wind in Utö, in the North Baltic, at times reached 27 metres/second. Snowstorms caused serious difficulties for Christmas traffic in all of Finland.

In December, wet snowfall and strong winds again felled trees on power lines. Northern Ostrobothnia was hit around the 10th, Southwestern Finland on the 23rd, and Southern Ostrobothnia on the 30th of December.

A white Christmas throughout Finland
Southern Finland enjoyed a proper snowy winter from January till the end of March. Eastern and Northern Finland were covered by a thick coat of snow until late April. In Northern Lapland the snow melted very quickly during the warm days of early May.

The first snows of the approaching winter were seen in Lapland in mid-September, and in some places in Southern Finland before mid-October. Thermal winter began in mid-November in all of Finland, and the largest snowfall of the season, over 30 cm, fell in central Helsinki and a narrow strip on the southern coast. For a long time, the thickest snow cover in the whole of Finland was on the coast, until more snow fell in Lapland at the end of November. All of Finland was white in early December, but by the middle of the month the edge of the snow had retreated to the Porvoo-Vaasa line. Just before Christmas, snowfall reached the southwestern parts of the country as well, and so Christmas was white throughout Finland. At the end of December, the snow cover thickness in Kittilä exceeded 50 cm. The end of the year was mild and rainy in large areas.

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