Like almost all of Finland, Joensuu has a temperate climate. More specifically, the city has a sub-arctic continental climate.
The effect of the Gulfstream, which warms all of Finland, is less in Joensuu than in southern and western Finland since Joensuu is relatively far from the coast. Temperatures in Joensuu are affected in spring by continuing cold weather from inland Russia and in autumn by long periods of warm weather. In comparison with Finnish coastal areas Joensuu has considerably more snow in winter.
Average temperature variations in Joensuu are substantial. In terms of actual plus/minus degrees mid-summer temperatures can rise as high as mid-winter ones can fall. Figures for summer rain are higher than those for winter snow.
The growing season for the Joensuu region, when the average daily temperature is greater than +5 ºC, is approximately 155 days. The length of the day and the season's early temperatures are important climatic features in regard to vegetation.
In addition to temperature, changes in the seasons are strongly linked with the changing length of the day, or the amount of sunlight an area receives. This is affected by inclination of the Earth's axis together with its revolution. In Joensuu the length of the day varies greatly between summer and winter: in summer it is very long and in winter periods of light are scant. The day is longest in the northern hemisphere, and in Joensuu it is at its longest at the summer solstice, around 22 June. At that time Joensuu gets more than 20 hours of daylight. Around the time of the winter solstice, about 23 December, the shortest day of the year, there is less than 5 hours of light in the city. Joensuu never, however, experiences polar night, when the sun does not rise. Day and night are equally long at the spring and autumn equinoxes, 21 March and 23 September, at all points of the globe.