September in Biysk averages a daily high of 18.5°C with nights around 5.2°C. Expect roughly 10.8 wet days totalling 37.8mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Biysk is May–September.
Based on BIJSK ZONALNAJA, RS (23.2km), 1995–2024. 30 years of September data.