May in Hillsboro averages a daily high of 20.1°C with nights around 7°C. Expect roughly 11.7 wet days totalling 46.8mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Hillsboro is June–September.
Based on PORTLAND HILLSBORO AIRPORT, OR US (3.8km), 1995–2024. 26 years of May data.