In winter temperatures range between 30 and 50 °F (−1 and 10 °C) and in summer between 68 and 86 °F (20 and 30 °C). Characteristic of the Po Basin, fog often shrouds the city in winter. The removal of rice fields from the southern neighbourhoods and the closure of most of the city’s heavy industry have reduced the phenomenon.

However, this has been offset somewhat by the growth of an almost uninterrupted built-up area around the city, which reduces local air circulation, and by the gray smog, or traffic-related air pollution, that often covers the city.