May in Longmont averages a daily high of 22.4°C with nights around 5.8°C. Expect roughly 10.3 wet days totalling 73.3mm. Comfortable conditions for being outdoors all day.
Across the year, the best time to visit Longmont is September–October.
Based on LONGMONT 2 ESE, CO US (2.1km), 1995–2024. 17 years of May data.