August in Janesville averages a daily high of 27.9°C with nights around 15.5°C. Expect roughly 10 wet days totalling 106.9mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Janesville is May–September.
Based on AFTON JANESVILLE WWTP, WI US (6.3km), 1995–2024. 30 years of August data.