Fort Smith has a subarctic climate with genuine extremes. Summers are short but surprisingly warm — July temperatures can reach 30°C and the days are very long. This is the best time to hike, canoe the Slave River, and watch wildlife in Wood Buffalo. The shoulder months of May and September bring mosquitoes in force (May/June) and the first serious cold (September), but also less crowding and some of the best photography light.
Winter runs from October to April, with temperatures regularly dropping to -30°C or colder. The payoff is spectacular aurora borealis — Fort Smith sits under the auroral oval and clear winter nights almost guarantee a display. The Slave River stays open longer than you might expect thanks to the rapids, attracting wildlife even in hard cold. Pack serious gear.