April in Longmont averages a daily high of 17.3°C with nights around -0.1°C. Expect roughly 7.2 wet days totalling 53.2mm. Generally workable, with some weather to plan around.
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 April data.