Predictable and calm climate
The maritime windstorms from the Atlantic are efficiently decayed by the Scandinavian Peninsula while the heatwaves and thunderstorms from the southeast continental regions do not reach Finland. For these reasons temperatures in summer or winter seldom reaches those experienced by neighboring regions on the same latitudes.
Neither weather-caused landslides nor hurricane force wind speeds have ever been recorded in Finland. There are typically one or two blizzards with heavy snowfall and strong wind gusts per winter, but the Finnish infrastructure copes with these well. Thus, the weather condition with greatest impact for datacenters is winds.
During the spring and autumn months, temperatures and the amount of sunlight hours change rapidly and the closeness of the Baltic Sea and the Northern Atlantic keep extreme temperatures mild.
The annual mean temperature in Finland is approximately +2.3 °C / 36.1 °F. Despite the fact that during summer months (Jun – Aug) temperatures can rise above 30 °C / 86 °F for a few days, the national average summer temperature is only 13.9 °C / 57.0 °F. Similarly, during the winter months (Dec – Feb) temperatures can occasionally fall below -20 °C / -4 °F in the south and even -40 °C / -40 °F in the north for a few days, the national average winter temperature is -8.7 °C / 16.3 °F. In comparison to other areas in the same latitudes (e.g. Siberia and south Greenland), the average winter temperatures are several degrees higher (up to 10°C / 50 °F). This is caused by the proximity of the Baltic Sea, large quantities of inland waters and, above all, the airflows from the Atlantic, which are warmed by the North Atlantic Drift (itself an extension of the Gulf Stream).
• The *30 year return level of the maximum temperature is approximately +31..+32 °C / 88..90 °F.
• The *30 year return level of the minimum temperature is approximately -30..-40 °C / -22..-40 °F, although in the north usually between -40..-45 °C / -40..-49 °F.
*30 year return level of temperature = temperature that occurs on average once in 30 years
There is no particular rainy or dry season in the Finnish climate. The most precipitation comes from showers during the summer months (Jun-Aug) and the most number of rainy days is in early winter (Nov-Jan).
• Precipitation below 0 °C / 32 °F: during worst blizzards, the snow depth can increase 20-40 cm / 0.7-1.3 ft in a day. The highest recorded snow depth increase in a day was 73 cm / 2.4 ft in 2016.
• Precipitation above 0 °C / 32 °F: the impacts of flash flooding are usually limited to flooded basements and bad road conditions, but fatalities are very rare. The highest recorded hourly rainfall amounts have been between 50 – 60 mm / 0.20 – 0.24”. The highest daily rainfall amount was 198 mm / 0.78” in 1944.
The prevailing wind direction over Finland is from the southwest, although the gustiest winds are usually between west and north. Winds can be considered the highest impact weather related risk for datacenters. Windstorms usually occur between October – January where as the most severe thunderstorms occurs during May – September timeframe.
Thunderstorms are typically much less severe than in Central- or Eastern-Europe for instance, but can every few years cause notable damage and few fatalities. A few strong to violent tornadoes have been reported in Finland in past decades although their probability in a single location is extremely low.
• There are no hurricane force wind speeds ever recorded in Finland.
• On the average approximately 14 tornadoes are reported each year, though they usually don’t cause significant damage.
• In inland areas wind gusts during storms are typically 20-30 m/s / 45-67 miles/h.
• The strongest windstorm in recent years was “Tapani” on December 26th, 2011. The highest inland wind gusts were around 31 m/s / 69.4 miles/h and the storm caused a few fatalities.