‘Heat dome’ unlikely to materialize in Toronto even as temperatures reach mid 30s

People eat lunch on a hot day in Toronto on Thursday, June 23, 2022. THE CANADIAN PRESS/Nathan Denette (Nathan Denette/THE CANADIAN PRESS)

Toronto will soon see the first official heat wave of the summer season, with temperatures forecasted to exceed 30 C in the coming days.

On Sunday, the mercury is expected to rise to a scorching 32 C, and an even hotter daytime high of 34 C is in the forecast on Monday. The blistering temperatures will stick around on Tuesday, which is expected see a high of 33 C.

In parts of the U.S., including Nebraska, Illinois, Wisconsin, and Iowa, the hot weather has prompted warnings from some experts who say a “heat dome” will create sweltering temperatures for millions of people in those regions.

But Toronto’s high heat and humidity may not qualify as a “heat dome,” CP24 Meteorologist Bill Coulter said, noting that while “all heat domes will deliver a heat wave, not every heat wave is a heat dome.”

He said a heat dome is created when an area of high pressure stalls, leading to stable air stagnating.

“Like putting a glass dome over a candle with nowhere for the generated heat to escape, that heat will continue to build under that area of high pressure,” he said.

“If an area of high pressure sits over an area during the warm weather months for a prolonged period, that stagnant air mass can continue to cook to very uncomfortable, even dangerous levels at the surface.”

Coulter said the weather in Toronto will just meet the criteria for a heat wave.

“Since we’ll get a bit of a break on Wednesday, there will be some debate as to whether it’s appropriate or not to use the term ‘heat dome’ when addressing our heat wave, as the high pressure here will not be as stagnant as (it is) over parts of the U.S.,” he said.

Coulter said Torontonians should try to enjoy the “cooler” weather this week while it is here.

Toronto will see a daytime high of 24 C on Thursday, feeling closer to 29 with humidity. Humid conditions will also make Friday’s high of 25 C feel about five degrees warmer, according to Environment Canada. The mercury is expected to rise to 28 C on Saturday.

“Embrace it. If is was going to be cool for the rest of the week and next week, it might be a little disappointing. Knowing that it is going to be incredibly hot and humid, especially Sunday, Monday and Tuesday, this is kind of a nice little breather before it comes in,” Coulter said Thursday.