May in Gresham averages a daily high of 20.4°C with nights around 8.9°C. Expect roughly 13.3 wet days totalling 67.5mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Gresham is June–September.
Based on PORTLAND TROUTDALE AIRPORT, OR US (6.1km), 1995–2024. 26 years of May data.