September in Viacha averages a daily high of 16.2°C with nights around -0.9°C. Expect roughly 6 wet days totalling 32.3mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Viacha is April–November.
Based on EL ALTO INTERNATIONAL, BL (19.1km), 1995–2024. 21 years of September data.