Cangzhou's North China plain climate means hot, humid summers (July and August reaching 35°C) and cold, often grey winters. Spring (April to May) and autumn (September to October) are the most comfortable for sightseeing. The Grand Canal heritage corridor is pleasant year-round but is at its best on clear autumn days when the water reflects the sky.
There is no particularly strong seasonal reason to time a visit, since the Iron Lion and canal are accessible year-round. As a day trip from Beijing or Tianjin the logistics are straightforward in any season.