September in Waltham averages a daily high of 23.9°C with nights around 11.1°C. Expect roughly 11.9 wet days totalling 87.9mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Waltham is May–June.
Based on BEDFORD HANSCOM FIELD, MA US (11.3km), 1995–2024. 27 years of September data.