June in Thornton averages a daily high of 29.4°C with nights around 11.8°C. Expect roughly 6.9 wet days totalling 37.2mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Thornton is September–October.
Based on NORTHGLENN, CO US (4.9km), 1995–2024. 29 years of June data.