Live weather alert map shows extreme heat warnings from Windsor to Timmins, Ont.

Your Morning meteorologist Kelsey McEwen has an update on heat in Ontario and Quebec.

Extreme heat and dangerous humidity with humidex values in the mid- to high 40s are affecting parts of the country, thanks to a heat dome covering a wide swath of Eastern Canada.

Environment Canada issued its first significant heat warning of the summer on Saturday for southern and eastern Ontario, and southern and western Quebec.

The Esri Canada map below, connected to live weather alerts from Environment Canada, shows the extent of the areas affected by heart warnings, from as far south as Windsor, Ont., to as far north as just south of Timmins nearly 700 kilometres away.

• ‘Heat dome’: Ontario, Quebec battle scorching temperatures

Parts of Ontario and Quebec are experiencing humidex values in the mid- to high 40s, CTV Your Morning meteorologist Kelsy McEwen said on Monday.

It’s all thanks to a large upper ridge of high pressure in the atmosphere that promotes “sinking air,” said McEwen, and as that air sinks it compresses and warms.

“So you get these hot parcels of air from the sun shining down at the surface, and they rise, and they sink, and they warm up even further,” she said.

Making things even more intense is a lack of movement of air in the lower atmosphere. “Pollution and air particulate matter can really settle in at the surface, so air quality can reduce,” said McEwen, meaning that children, those with respiratory issues, those who are pregnant and the elderly should all take precautions.

“Not only in terms of breathing, but also in (their) limited ability to regulate body temperature.”

McEwen said there will be a slight reprieve in temperature and humidity by Wednesday as drier air slowly moves in.

“Today is probably the worst of the days,” she said.

Severe thunderstorms

It’s not just extreme heat that’s on the radar, with Environment Canada alerting widespread severe thunderstorm watches in the Thunder Bay area and in northeast Ontario around Timmins.

Areas affected by rainfall warnings can be seen in blue in the above map. Environment Canada says Manitouwadge–Hornepayne in northwestern Ontario has already received up to 50 mm of rain, as heavy showers and thunderstorms continue to move through the area.

“Heavy downpours are likely to cause flash floods and water pooling on roads. Localized flooding in low-lying areas is possible,” said Environment Canada.

With files from the Canadian Press