May in Washington averages a daily high of 15.7°C with nights around 6.7°C. Expect roughly 12.9 wet days totalling 46.1mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Washington is June–September.
Based on DURHAM, UK (15.3km), 1995–2024. 27 years of May data.