May in Kostroma averages a daily high of 18.4°C with nights around 7.2°C. Expect roughly 11.6 wet days totalling 51.8mm. 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. 25 years of May data.