September in Białystok averages a daily high of 18.5°C with nights around 7.3°C. Expect roughly 10.4 wet days totalling 52mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Białystok is May–September.
Based on BIALYSTOK, PL (3.7km), 1995–2024. 30 years of September data.