When visiting Hamilton, make sure you wear layers of clothing, which can prepare you for whatever part of the city you’re in: Hamilton’s climate of the lower city (downtown) is in general much more sheltered and milder than on top of “the mountain”.
Overall, though, Hamilton has a humid continental climate, one which is relatively mild compared with most of Canada. The average January temperature is -3.6C (26.5F) but most days rise just above freezing making for slushy conditions during snowfalls. Winter snowfall averages 113cm (44″) with great year-to-year variation. The average July temperature is 22.5C (72.5F) and humidity is usually high during the summer, May through early October.
In the winter, it is not uncommon for lower city residents, with no snow present in their neighborhoods, to drive up into the upper city and be surprised at encountering a thick blanket of fresh white snow. The escarpment also affects summer weather; temperatures downtown are many degrees warmer, particularly at night, and often an inversion will combine with the physical barrier of the escarpment to trap smog in the downtown area, sometimes reducing downtown visibility to less than 2km.