Winter is long, dark and cold. It can also be spectacularly beautiful. First snow in Helsinki can be as early as October. Snow instantly brightens up the city, making the winter darkness much more bearable—especially on a clear and sunny day. Because of its closeness to the sea, Helsinki tends to be significantly warmer and damper than places inland, where winters tend to be cold, clear and crisp. Hours of daylight in winter are short, typically 10 am-4 pm, and decrease as you go north. Temperatures can fall rapidly as you move out of the urban environment, and a drop of five degrees over a mile/kilometer or two is not unknown.
Spring is brief, usually lasting April and May. Change is very rapid, and plants can spring into bloom in a day. However, because of melting snow, the season tends to be damp everywhere. March-early May is probably not the best time to visit Finland.
Summers are long and sometimes surprisingly hot, with temperatures of 85 F/29 C not uncommon. Daylight lasts about 3 am-11 pm. In fact, at midsummer in Helsinki, there may be almost complete daylight. Some people have difficulty sleeping. Fortunately, most hotels and apartments are fitted with lightproof blinds.
Fall is short but beautiful, with wonderful displays of foliage on the trees. The colorful part of Finnish fall is called ruska. When the skies are clear, temperatures can fall rapidly at night, though this is less noticeable in the city itself.