September in Irkutsk averages a daily high of 16.2°C with nights around 4.5°C. Expect roughly 10.6 wet days totalling 46.9mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Irkutsk is May–August.
Based on IRKUTSK, RS (5.2km), 1995–2024. 25 years of September data.