Bolu's climate is marked by a significant variation in temperatures throughout the year. Winters are chilly, with average temperatures ranging from 6-8°C, and occasionally dropping as low as -16°C in January. Spring brings a gradual warming trend, with temperatures rising to an average of 11-19°C by April and May. Summers are warm to hot, with July and August averaging around 25°C but reaching highs of up to 39°C. Autumn is mild, with temperatures dropping back down to around 12-14°C in October and November before cooling further into winter.