December in Great Falls averages a daily high of 1.8°C with nights around -7.8°C. Expect roughly 6.3 wet days totalling 19.3mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Great Falls is August–September.
Based on GREAT FALLS 16ST, MT US (2.1km), 1995–2024. 15 years of December data.