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Heat warnings are still in effect for most of Ontario, and stretch into Quebec as far as Montreal.

Hottest day of the week cranks up the heat in southern ON

Digital writers

Wednesday, July 29, 2015, 5:48 PM - Heat warnings are still in effect for large swaths of southern and northern Ontario, and stretch into Quebec as far as Montreal.

An Extreme Heat Alert has been upgraded by the City of Toronto. Cooling centres are open across the city to help residents cope with scorching temperatures.

Toronto and Ottawa both issued heat alerts on Monday, extended into Wednesday, as have other communities.

On Tuesday evening, Air Quality Ontario issued an air quality advisory due to "high levels of pollution" caused, in part, by the stagnant airmass that's parked over the region. Though the advisory was dropped later a few hours later, there is a good chance another could be issued Wednesday -- poised to be the hottest day of the week.

Daytime temperatures are expected to reach a high of 32 degrees Celsius -- but will feel closer to a stifling 40 degrees with the humidex. 

Intense heat has the potential to once again produce dangerous air levels.

"Individuals may experience symptoms such as increased coughing, throat irritation, headaches or shortness of breath," the air quality statement reads.

"Children, seniors and those with cardiovascular or lung disease, such as asthma, are especially at risk. If you, or someone in your care, develop symptoms, reduce or reschedule strenuous outdoor activities where ever possible until the air quality improves."

What to expect

Heat warnings are typically issued by Environment Canada when very high temperature or humidity conditions are expected to pose an elevated risk of heat-related illnesses, such as heat stroke or heat exhaustion.

Southern Ontario's Tuesday’s highs were between 32oC and 33oC before factoring in the humidity, and that was enough to break records in some places.

That trend continued on Wednesday, where even more records were broken.

Downtown Toronto is expected to be at or above 30oC until Thursday.

On Wednesday afternoon temperatures largely settled in the low-mid 30s away from the lake, but felt closer to 40.

Environment Canada advises adequate hydration by drinking water before you start to feel thirsty to decrease the risk of dehydration.

The heat, combined with a weak front pushing through the province, will bring the risk for non-severe thunderstorms and scattered showers to extreme southwestern Ontario and Cottage Country through Wednesday evening. 

Farther north, storms will flare up as far as Hudson's Bay in Ontario and Quebec. By Thursday, the storm threat rolls through southern Quebec, including Montreal.

A look ahead

Later in the week, a weak front will move through during the pre-dawn hours Thursday, bringing light showers and thunderstorms to southern Ontario.

A modest-cool down is forecast for Thursday and Friday, with temperatures expected to dip into the upper 20s to high 30s, which despite being seasonal will feel significantly cooler after the hot and humid start to the week.

SOURCE: The Weather Network

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