September in Castle Rock averages a daily high of 25.5°C with nights around 8.4°C. Expect roughly 6.1 wet days totalling 35.3mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Castle Rock is May–June.
Based on CASTLE ROCK, CO US (1.7km), 1995–2024. 29 years of September data.