Normally the temperature of Rouen is about 25°c during summer. In winter season the climate is not too cold and it hardly snows. As it is located near seaside, it regularly rains. It has slight humid climate in summer but not too dry.
Winter: The best time to visit this city as the climate will be mild. So you can enjoy in this season if you don’t want crowd around you. Though it is winter but you don’t have to bring heavy coats as the temperature will be about mid -40°c.
Summer: Also a good time to visit. The average temperature during this season would be about 61°c or 64°c.