Though Toronto winters can be snowy and cold, the weather is usually less severe than in cities along the southern shore of Lake Ontario. January temperatures range 18-31 F/-8 to -1 C. Occasionally, Toronto will experience a lake-effect storm and temperatures dip to -25 F /-32 C. Summer in Toronto can be quite warm and fairly humid. Midsummer temperatures range 61-81 F/16-27 C, with quite a few days in the 90s F/32-35 C. It's sunniest then, with some spectacular thunderstorms occurring around the lake.
Smog advisory days are common in the summer months, so check the weather report before leaving home if air quality will hinder your ability to enjoy the outdoors. People generally affected include the elderly, young children and those with allergies and asthma. In general, the weather is most comfortable in late spring or early autumn, when it's 46-71 F/8-22 C, but if you go in July or August, you will be able to see all of the outdoor attractions.