Toronto gets brief relief but no long-term shelter from extreme heat

A heat warning in effect for the past week across the Greater Toronto Area was lifted on Friday as temperatures in the region returned to seasonal averages.

But Toronto residents should get used to sweating through more days of extreme heat, according to a senior climatologist.

"The trends have shown us that we are living in warmer times and all indications are that this kind of trend is going to continue," David Phillips, senior climatologist with Environment Canada, told CBC Radio's Metro Morning.

Phillips recently analyzed weather trends over the past 100 years and pointed to increasing numbers of "tropical" nights and days above 30 C as indications that sweltering days will likely be a common feature of Toronto's future weather. 

"Clearly what we're seeing is what Torontonians didn't have to deal with 100 years ago," Phillips said.

You can listen to the full interview with Phillips below.

Phillips defines a tropical night as one during which temperatures remain above 20 C. Toronto has seen four instances in the past week with nighttime temperatures above 20 C, which is more than the total yearly average from 100 years ago, he said.

A similar trend emerges for days with temperatures over 30 C. The average number of days above 30 C a century ago was seven. This year, Toronto has seen 20 such days already, Phillips said, with maximum temperature recordings inching increasingly higher. 

Bermuda High to blame

Phillips said the duration of the recent heat wave was also significant.

"To go on for seven or eight days with temperatures like this is not unprecedented for Toronto, but certainly it's something we haven't seen in about 17 years," he said.

The underlying cause of the heat wave, which baked the northeastern U.S. and six provinces over the past week, was "no mystery."

It was caused by a phenomenon known as a Bermuda High, a high pressure system that brought hot and humid air from the Gulf of Mexico and kept it centred over the Great Lakes region, without any other weather systems interrupting it, he said.

"It's just like taking the barbecue lid and putting it down over humanity and cooking."

In response to the sustained heat, the city opened seven cooling stations in local community centres across the city and extended hours at public swimming pools.

Weather for the weekend

Temperatures this weekend are expected to return to more comfortable levels, Phillips said.

According to Environment Canada, Toronto will see a daytime high on Friday of 25 C, though it will feel more like 28. The Saturday high is expected to be 26 C and Sunday is forecast to be 29 C.

Phillips said the heat wave is a harbinger of what's to come in July and August and Ontario residents should get used to the warmer weather.

"The summer we're going to get, very unlike last year, which was cool and wet, this one's going to be dry and hot," he said.