December in Flagstaff averages a daily high of 6.5°C with nights around -8.1°C. Expect roughly 6.5 wet days totalling 44.6mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Flagstaff is May–June.
Based on FLAGSTAFF AIRPORT, AZ US (6.1km), 1995–2024. 30 years of December data.