Central Canadian Shield forests
This ecoregion consists of rolling hills, lakes, bogs and rocky outcrops covering a large curved swathe on the Canadian Shield from eastern Manitoba and Northern Ontario running southeastwards through Thunder Bay District to the north shore of Lake Superior and then northeastwards into western Quebec. The area has a cool climate with summer temperatures averaging around 13°C dropping to a very cold -17°C in winter, with the hills around Lac Seul in northwestern Ontario being warmer and wetter than most of the area. Average rainfall in the eastern side of the ecoregion is 550mm per year, rising to 750mm in the centre (near Lake Nipigon for example), up to 900mm in the west. Specific areas include Lake Nipigon and Big Trout Lake (Ontario). These forest contrast with more severe boreal forest ecoregions such as the Eastern Canadian Shield taiga to the north, which covers most of Northern Quebec and Labrador.
Ontario
The climate of Ontario varies by season and location. It is affected by three air sources: cold, dry, arctic air from the north (dominant factor during the winter months, and for a longer part of the year in far northern Ontario); Pacific polar air crossing in from the western Canadian Prairies/US Northern Plains; and warm, moist air from the Gulf of Mexico and the Atlantic Ocean. The effects of these major air masses on temperature and precipitation depend mainly on latitude, proximity to major bodies of water and to a small extent, terrain relief. In general, most of Ontario's climate is classified as humid continental. Ontario has three main climatic regions.