Wudalianchi is a three-season destination. The winter is severe enough (-30°C or colder) to make geological sightseeing unpleasant, and most tourist infrastructure operates only during warmer months.
Summer (June–August) is the main visitor season. The lakes are navigable, the walking trails are accessible, and the mineral spring bathing facilities are at full operation. It is also when Chinese health tourists arrive in numbers — the town fills considerably. Temperatures are warm but the altitude and open lava fields can make direct sun intense; bring sun protection.
Spring (late April–May) is underrated. The snow melts from the lava fields revealing the black rock against the remaining white, the lakes open up, and visitor numbers are low. Temperatures can still be cold (occasional frost in May) but the clarity is excellent.
Autumn (September–October) is similar to spring: quieter, cooler, with excellent light on the volcanic landscape and the forest beginning to turn. This is arguably the best season for photography.
The health tourism side of Wudalianchi operates primarily in summer and early autumn, so if mineral spring bathing is the goal, plan accordingly.