We think Quebec City is best in summer, although fall and spring can also be pleasant. The city's weather can be extreme, from hot and humid in summer to very cold and snowy in winter.
Average highs in January are around 18 F/-8 C and lows around 1 F/-17 C. Winter Carnival is a wonderful celebration, but with an average of 28.7 in/73 cm of snow in January alone, you'd better be prepared for the weather (take along your snow gear).
During high cruise season (late April-early October), when many ships ply the St. Lawrence, expect lows from 35-55 F/2-13 C and highs in the 50s-70s F/11-25 C. Rainfall during that period is about 5 in/13 cm a month. For 24-hour weather information, phone 418-648-7766 or visit http://www.weatheroffice.gc.ca.