September in Kostroma averages a daily high of 15.7°C with nights around 7.2°C. Expect roughly 11.9 wet days totalling 58mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Kostroma is May–August.
Based on KOSTROMA, RS (5.9km), 1995–2024. 24 years of September data.