September in Waukesha averages a daily high of 23.3°C with nights around 10.7°C. Expect roughly 8.2 wet days totalling 84.5mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Waukesha is June–September.
Based on WAUKESHA WWTP, WI US (2.2km), 1995–2024. 20 years of September data.