Heat dome threatens to smash London record high set in 1936

The temperature in London is expected to soar to a sweltering 35 C as a heat dome blankets central Canada

As this summer sizzles along, remember that one of the great joys of living in Southwestern Ontario is that we get to experience all four seasons to their extremes. So, on Tuesday, when the temperatures are expected to soar to a sweltering 35 C, while you are sweating it out, think about those frigid, snowy days of January and February when we never thought the winter of 2026 would end. Though it’s going to be super-hot on Tuesday, the forecast temperature is expected to come in a smidge under the record for July 14 in the London area of 36.1 C, set in 1936.

“We’re going to be close,” Geoff Coulson, an Environment Canada meteorologist, said Monday. With the humidity, the temperatures will feel more like the low to mid-40s C. Coulson said the area is “tapping into a large heat dome,” a large high-pressure system centred over Iowa. There are heat advisories, heat warnings and heat alerts extending from Montana, through the Dakotas, Minnesota, Wisconsin, Michigan, Manitoba, all of northern Ontario, parts of Quebec, New York, Ohio and Pennsylvania.

“This is a large-scale weather phenomenon,” Coulson said. “We’re starting to get it ourselves here in Southwestern Ontario, but it’s actually been giving extreme heat already to parts of the Upper Plains, the Prairies and northwestern Ontario beginning on the weekend.” The latest heat wave isn’t a surprise to forecasters who had already pegged July to be warmer than normal this year.

Heat domes aren’t unusual in July – the deadly heat dome in 2021 in British Columbia and Washington state brought the term into more common usage – and Coulson said the weather term refers to a large-scale high-pressure system “that intensifies the warming of an already very warm and humid air mass.” Though Tuesday is expected to be the hottest day of the week, the heat will hang around Wednesday and Thursday before we get less humid conditions on Friday and Saturday. And we could see some rain across the area late Friday into Saturday.

Environment Canada has issued a yellow alert for the region, part of its relatively new weather warning system. Yellow, the most common alert, signifies possible “damage, disruption or health impacts” caused by weather conditions and “impacts are moderate, localized and/or short-term.” To endure the hot Tuesday, Coulson advises people to find a cool place to take it easy and “to keep an eye on the most vulnerable in these situations which is the really young and the elderly.”

And if you need to be outside, take frequent breaks and stay hydrated.