The humid continental climate in Helsinki is influenced by both maritime and continental climate patterns. The city has a typical climate for a coastal city: it is often windy and rain arrives often from the sea. However, due to the Gulf Stream, the climate is more temperate than in other areas along the same latitude. The summer season in Helsinki begins in May and lasts until mid-September. The average summer temperature - for day and night - is around 15°C. On hot days the temperature can rise to around 30-degrees. Helsinki is usually at its warmest in July.
The winter season begins in November or early-December, when temperatures vary either side of 0°C. The average temperature between December and February is around -4°C. The coldest time of the year is usually around the end of January, when temperatures can fall to below -15°C and the sea is often frozen. During the winter months, especially in January and February, cold spells of -20°C are not unusual. The coldest temperature ever recorded in Helsinki was -34.3°C in 1987. Spring arrives late in Helsinki, usually around April.
In northern Finland above the Arctic Circle, the sun does not set for 73 days, so it stays light on summer nights. In the same area, the sun stays below the horizon for 51 days in winter, forming a period of uninterrupted winter darkness.
Average annual temperature: +5.3°C.
Average January temperature: - 5°C ( 23°F ).
Average July temperature: 18°C ( 64°F ).
Annual rainfall: 600mm ( 23.6 inches ).