The climate of Kuusamo is cold continental, with freezing winters and mild summers.
The city is located in eastern Finland, in North Ostrobothnia, and a short distance from the Russian border. It is true that we are at the 65th parallel, therefore just south of the Arctic Circle, but due to atmospheric refraction, one can observe the sun at midnight from June 14th to 29th. Furthermore, the white nights, when the sun sets but it is not completely dark even at midnight, occur from April 23rd to August 21st.
The average temperature of the coldest month (January) is of -13.2 °C (8 °F), that of the warmest month (July) is of 14.6 °C (58 °F). Here are the average temperatures.
Kuusamo - Average temperatures
Min (°C)-17-17-12-6071083-2-9-14
Max (°C)-9-8-3310161916103-3-7
Min (°F)111021324550463728167
Max (°F)161827375061666150372719

Precipitation amounts to 595 millimeters (23.4 inches) per year: so, it is at an intermediate level. It ranges from 30 mm (1.2 in) in the driest months (February, April) to 80 mm (3.1 in) in the wettest (July). Here is the average precipitation.
Kuusamo - Average precipitation


Best Time

The best time to visit Kuusamo is the summer, from June to August, since it is the mildest season. However, you must take into account some rainy days and a bit of cold at night.