Ontario Geography & Climate

Ontario is larger than France and Spain combined, and is split into two very different halves.

The Great Lakes

The province borders four of the five — Superior, Huron, Erie and Ontario — which together hold around a fifth of the world’s surface fresh water. Superior is the largest freshwater lake on earth by area, cold enough that it rarely warms above single digits, and its north shore is cliffed and empty. The lakes moderate the climate, drive lake-effect snow, and carry shipping through a system of locks to the Atlantic.

The Canadian Shield

North and east of a line running roughly from Georgian Bay to the Ottawa river, the land is exposed Precambrian rock — some of the oldest on the planet — scraped bare by ice and left with a thin soil, endless conifer and birch forest, and something in the order of a quarter of a million lakes. It is beautiful, close to empty, and the reason Ontario’s wealth was historically mining and timber.

The southern peninsula

Below the Shield, a wedge of flat glacial farmland between lakes Huron, Erie and Ontario holds the great majority of the population. The Niagara Escarpment, a limestone ridge running some 700 kilometres from Niagara to the Bruce Peninsula, is a UNESCO biosphere reserve and carries the Bruce Trail along its length.

Niagara

The Niagara river drops about 51 metres at the Horseshoe Falls, carrying more water than any other waterfall in North America, and the whole gorge has retreated some eleven kilometres upstream since the ice retreated.

The far north

Muskeg lowlands running to the salt water of James Bay and Hudson Bay, with polar bears at the northern edge.

Ontario has a continental climate with four distinct seasons and a wide annual temperature range, moderated near the lakes and severe away from them.

Summer

June to August is warm to hot: Toronto averages 21 to 27°C with high humidity, and heat waves push the felt temperature well above 35°C. The north is cooler and the lakes are warm enough to swim in by mid-July.

Winter

December to March is cold. Toronto sits around minus 6 to plus 1°C; Ottawa is considerably colder, regularly below minus 20 at night, and is one of the coldest national capitals in the world. Snow is reliable outside the immediate lakeshore.

Lake effect

Cold air crossing warmer open water picks up moisture and dumps it downwind, which is why the snow belts east of Lake Huron and Georgian Bay measure their annual snowfall in metres while the lakeshore a short distance away gets much less. The same effect delays autumn frosts on the Niagara peninsula, which is what makes the wine industry possible.

Autumn

September and October bring clear, cool weather and the maple colour, which peaks in the north in late September and in the south in mid-October.

Spring

Slow, wet and unreliable, with the thaw producing mud and blackflies in the north.

A warming winter

The trend is visible in things people organise their year around. The Rideau Canal skateway, which once opened reliably in early January for fifty-odd days, has had seasons cut short and one in which it did not open at all; ice roads in the far north are usable for fewer weeks; and the Niagara fruit belt is seeing earlier bud break and more frost damage as a result.

Storms

Summer thunderstorms are frequent and occasionally severe, and ice storms happen.