December in Barreiro averages a daily high of 15.3°C with nights around 9.6°C. Expect roughly 11.8 wet days totalling 116.4mm. Generally workable, with some weather to plan around.
Across the year, the best time to visit Barreiro is May–September.
Based on LISBOA GEOFISICA, PO (9km), 1995–2024. 25 years of December data.