Inari is located 300 km north of the Arctic Circle. There is Midnight Sun
from late May to late July and the last ice in the lake often disappears only at the end of May. Even in July, the average temperature is only around 17°C and temperatures, on occasion, can be just above freezing at night. There of course an also be days where the temperature is well above 20°C. So expect the unexpected and have at least some warm layers if visiting in summer. Winter is usually extremely cold and be prepared for temperatures dropping to as low as -30C. There are not many shopping options in Inari for warm clothing so its best to arrive with adequate clothing and layers to keep yourself warm.
For up to date weather, check out the Inari forecast on the FInnish Meteorological Institute.