Curitiba sits at 900 metres above sea level on the Paraná plateau, which keeps the climate noticeably cooler than coastal Brazilian cities. Expect mild summers and genuinely cold winters — frost is not unusual between June and August, and temperatures can drop to near zero overnight.
The best time to visit is March to May and September to November: the weather is comfortable (15–22°C), the city is not crowded with tourists, and the Serra Verde Express train to Paranaguá runs on a regular schedule. December and January are hot and humid with frequent afternoon thunderstorms, but the city stays lively and the parks look their greenest.
Winter (June–August) is cold but dry, and the araucária forests in the parks look beautiful in the clear winter light. The Festa do Divino Espírito Santo in Pentecost is a major event in the city's Ukrainian and Polish communities and worth timing a visit around if you are interested in the immigrant cultural heritage.