September in Rockville averages a daily high of 27.1°C with nights around 15.7°C. Expect roughly 9.3 wet days totalling 117.1mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Rockville is April–May.
Based on DALECARLIA RESERVOIR, MD US (16.5km), 1995–2024. 28 years of September data.