07/29/2015 10:05 EDT | Updated 07/29/2016 05:59 EDT

Sizzling Ontario temperatures may break summer record

Toronto could see the hottest day of the year on Wednesday as a sizzling heat weave continues across Southern Ontario. 

The city will see a high of 34 C, but with the humidity factored it, it will feel more like 40 degrees, Weather Network meteorologist Tyler Hamilton said.

The highest temperature ever recorded at Pearson International Airport was 38.3 C on Aug. 25, 1948. A temperature of 40.6 C was recorded in July 1936 at a downtown Toronto station that is relied on less for records because it has moved around over the years.

Wednesday's forecast prompted Toronto's medical officer of health to issue an extreme heat alert. Seven cooling centres have opened across the city. Ottawa has also issued a heat alert.

Late Tuesday evening, Environment Canada issued an air quality warning for the Greater Toronto Area due to high levels of ozone, but it cancelled the warning after a couple hours.

But it's not just the big city that's facing sweltering temperatures Wednesday. Environment Canada has issued a heat alerts for the following Ontario areas:

- Ottawa-Gatinea.

- Hamilton.

- Niagara.

- Smiths Falls-Lanark-Sharbot Lake.

- Halton-Peel.

- York-Durham.

- Belleville-Quinte-Northumberland .

- Prescott and Russell.

- Stirling-Tweed-South Frontenac.

- Brockville-Leeds and Grenville.

- Prescott and Russell.

- Cornwall-Morrisburg.

- Kingston-Prince Edward.

The government agency urges people in the affected areas to watch for symptoms of heat illness of dehydration, including headaches, nausea, dizziness, extreme thirst, rapid breathing and heartbeat, decreased urination or dark-yellow urine.

"If you experience any of these symptoms during extreme heat, immediately move to a cool place and drink liquids. Water is best," Environment Canada said.

"Frequently visit neighbours, friends and older family members, especially those who are chronically ill, to make sure that they are cool and hydrated."

Thunderstorm warnings

The heat, combined with a weak front pushing through, brings the threat of non-severe thundershowers Wednesday evening in southwestern Ontario and Cottage Country, according to The Weather Network. Storms are also expected further north, in the Hudson's Bay area and Quebec.

By Thursday, the storms are expected to hit southern Quebec, including Montreal.