Porvoo's winters are long and cold, with temperatures often dropping below -20°C in January and February. Spring is a gradual warming, with April and May bringing temperatures that can rise above 10°C on warmer days. Summer is mild to warm, with highs occasionally reaching 30°C in June and July, but averaging around 15-20°C for the season. Autumn brings a return of cooler temperatures, with October and November seeing temperatures often below freezing.