Ontario, Quebec, large swathes of U.S. swelter under heat dome

CBC

23-06-2025

Much of Ontario and southwestern Quebec will continue to bake in high temperatures on Monday and Tuesday as a heat dome lingers over the region.
Environment Canada issued a heat warning for the area on Saturday, saying hot and humid conditions will likely continue until Wednesday.
The dangerously high temperatures are expected to affect communities from southwestern Ontario and north to Sudbury and Timmins.
In Quebec, the hottest temperatures are expected to be felt from Montreal to Shawinigan and north to Abitibi.
Environment Canada meteorologist Julien Pellerin said he expects Ontario and Quebec to hit their peak daytime highs on Monday and Tuesday with temperatures rising above 30 C, and the humidex making it feel more like 40 to 45 C, depending on the region.
"It won't last very long," he added. "By the end of Tuesday and Wednesday, we will have a transition in air mass all over Canada, especially over Quebec and Ontario."
Heat levels in Ontario and Quebec led Environment Canada to remind people to stay hydrated by drinking water before they're thirsty, to watch for early signs of heat exhaustion and not overexert themselves.
"Be careful; you know yourself," Pellerin said. "Make sure you're aware of what you're feeling and take breaks, Make sure you have a location where you can rest with the air conditioning."
In Quebec, schools are being urged to stay vigilant with the rising temperatures.
In a letter from the assistant deputy education minister, schools were encouraged to "put in place all the preventive measures you judge necessary to ensure everyone's security."
"Depending on the situation, these measures could go all the way up to closing one or more schools for the day of June 23," said the message signed by Stephanie Vachon.
Pellerin says scorching temperatures over the eastern part of the continent are causing below-normal temperatures in other regions, which have led to warnings of wet snow and heavy rain in the West.
"If you have a heat dome on a sector, you can expect colder air in another sector, so that's what the Prairies are currently experiencing," Pellerin said on Sunday.
On Saturday, Environment Canada warned that areas in British Columbia could face heavy showers and the possibility of wet snow.
Heavy rainfall advisories that had been in effect in southern Alberta were all lifted by Sunday, but the region received significant precipitation.
The Calgary Fire Department advised against boating and all other water activities on the Bow River due to higher-than-normal water flow, although the city said flooding over riverbanks was not expected.
Saskatchewan's Water Security Agency warned the Alberta rain could also lead to increased flows on the South Saskatchewan River between the Alberta boundary and Lake Diefenbaker.
The agency said Alberta began dumping water from reservoirs this past week to make room for the additional runoff.
It expected lake levels at Lake Diefenbaker, a large reservoir northwest of Regina that's a popular recreation area, to rise over a metre this week as a result of the weather system.
'Everywhere east of the Rockies': U.S. meteorologist
A heat dome occurs when a large area of high pressure in the upper atmosphere acts as a reservoir that traps heat and humidity, according to the U.S. National Weather Service.
In the U.S., most of the northeastern quadrant of the country from Minnesota to Maine was under some type of heat advisory. So were parts of Arkansas, Tennessee, Louisiana and Mississippi, the National Weather Service said.
Mark Gehring, a National Weather Service meteorologist in Sullivan, Wis., said this level of heat is not uncommon during the summer months in the U.S., although it usually takes hold in mid-July or early August. The most unusual facet of this heat wave is the sheer amount of territory sweltering under it, he said.
"It's basically everywhere east of the Rockies," he said, referring to the Rocky Mountains. "That is unusual, to have this massive area of high dewpoints and heat."
Forecasts in Philadelphia called for a heat index of 108 F (42.2 C) on Monday.
The heat is expected to persist this week with the highest temperatures shifting eastward. New York City is expected to see highs around 95 F (35 C) on Monday and Tuesday, and Gov. Kathy Hochul declared a state of emergency in 32 New York state counties due to the strong storms and forecast extreme heat.