I looked that up on the Finnish Meteorological Institute web page here. Relative air humidity dropped from 99% at 6.10 am when the sun rose to 22% at 6 pm. This is not uncommon for early summer. The lakes and rivers or sea water in or near Northern Europe have not had time to warm up yet but the sun is quite powerful already - by local standards. Late summer nights are different. Air humidity is higher which is why the temperature will not drop that low before dawn.
This warm spell seems unlikely to end in powerful thunderstorms - unless it goes on long enough - because the air mass that we are in is simply too dry. Because of the greater humidity of the air in late July and August hot weather then will usually end in torrential rain and small tornadoes. In the less densely populated regions in Eastern Finland, tornadoes may destroy power lines and cause blackouts lasting several days to a week. I have lived all my life in the southwest of the country. I don't remember any power outages caused by weather phenomena ever or anything at all since my childhood.
