May in Castlereagh averages a daily high of 15.5°C with nights around 7.4°C. Expect roughly 14.9 wet days totalling 65.7mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Castlereagh is June–September.
Based on STORMONT CASTLE, UK (4.9km), 1995–2024. 29 years of May data.