September in Washington averages a daily high of 27°C with nights around 17.8°C. Expect roughly 8.7 wet days totalling 98.7mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Washington is April–May.
Based on WASHINGTON REAGAN NATIONAL AIRPORT, VA US (5.3km), 1995–2024. 30 years of September data.