Why is Ottawa colder and have a lot more snow than Toronto?
Ottawa does have a lower mean temperature during the winter which, on its own, allows for greater snowfall. During mild winters, Toronto often sees snow mixed with rain while Ottawa receives snow which can change into freezing rain. This reflects the fact that Ottawa is farther north, and Toronto can be moderated by the waters of Lake Ontario. When areas of low pressure pass through the Great Lakes, the attendant warm front often lies between Toronto and Ottawa, separating a cold air mass to the north (Ottawa), from a warmer air mass to the south (Toronto). The wind field in the vicinity of the front can help enhance this difference in temperature at the surface. Perhaps more importantly, Montreal and the eastern Ottawa valley are on the fringe of a storm track that draws powerful storms from the Atlantic seaboard to the north towards the US northeast. Montreal and Ottawa are often on the back side of these systems, where the air is quite cold, and can see significant snowfall. Toronto
