May in Janesville averages a daily high of 21.1°C with nights around 8.9°C. Expect roughly 13.1 wet days totalling 104.9mm. Generally workable, with some weather to plan around.
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 May data.