Finland Travel Guide
Yours truly, can expect warm (not hot) days in Helsinki from mid-May, and in Lapland from mid-June until September. The midnight sun can be seen from May to July, depending on the region. For a period in midwinter, the northern lights almost make up for the fact that the sun does not rise at all. Even in Helsinki, summer nights are brief and never really dark, whereas in midwinter, daylight lasts only a few hours.