January in Thornhill averages a daily high of -0.9°C with nights around -8.4°C. Expect roughly 13.7 wet days totalling 66.3mm. A hard month to visit for comfort alone.
Across the year, the best time to visit Thornhill is May–September.
Based on TORONTO NORTH YORK, ON CA (4.9km), 1995–2024. 28 years of January data.