Sizzling temperatures and the threat of storms blanket much of the country in weather warnings

Temperature records in some municipalities could run aside tues as cinque provinces and 1 territory sit under Environment Canada weather alerts that warn of poor air quality, extreme heat and thunderstorms.

All but Ontario's northernmost regions are under heat warnings, with temperatures in the mid- to high-30s C and humidity making it feel like the mid-40s.

Heat or air quality warnings are also in place to the west, in Manitoba, Saskatchewan and the Northwest Territories.

To the east, Environment Canada is warning of the potential for hazardous storms in Quebec and New Brunswick, including an orange tornado watch in the area between Montreal and Quebec City, including Drummondville, Trois-Rivières and Shawinigan.

"Significant damage or destruction to infrastructure, homes and the natural environment is possible," the tornado watch warns.

The culprit for most of the warnings is a massive area of high pressure centred in the U.S. That has "generated heat advisories, heat alerts, heat warnings in areas across the Upper Plains states of the U.S., parts of Manitoba, across Ontario, the Great Lakes states as well and even into the province of Quebec," Environment Canada meteorologist Geoff Coulson said Monday.

"It's a wide-ranging system that's bringing much above seasonal temperatures."

Ottawa's forecasted high of 35 C would be the hottest day of 2026 so far. It and other cities in southern Ontario, including Toronto, could set daily heat records.

The hottest-ever July 14 recorded at Toronto's Pearson airport was in 1995, when temperatures hit 36.7 C with a humidex that felt like 50 C, according to Environment Canada's website. Tuesday's expected high is 37 C.

Much of northern Ontario, from Kenora and Thunder Bay to Fort Hope and Timmins, is under a severe orange heat warning, while the rest of the heat warnings are in the lower yellow category.

Northern Ontario has lower thresholds for triggering the weather agency's heat warnings, which are based on historic norms and potential impacts; for instance a 36 humidex in the north compared to a 40 humidex in the south.

Municipalities across the country including Ottawa have opened cooling stations and pools for residents to keep out of the heat.

Environment Canada recommends watching for early signs of heat exhaustion, which can include a headache, nausea, dizziness, thirst, dark urine and intense fatigue.

Anyone showing signs of heat stroke should call 911, it said. Symptoms of heat stroke include red and hot skin, nausea, dizziness, confusion and change in consciousness.

Withering heat grips eastern Ontario, western Quebec

Severe thunderstorm watch, tornado risk issued for much of southern Quebec

The agency is also urging the public to turn on air conditioning, drink water often, close their blinds and limit exposure to the sun. Residents should wear lightweight, light-coloured and loose-fitting clothing, as well as a hat.

In addition to the heat, people in some regions are also experiencing smoke in the air from forest fires.

"We've got in some cases a significant wildfire activity, especially to the west of Thunder Bay," Coulson said. "With the winds coming in from the west, we're seeing plumes of this wildfire smoke moving eastwards towards the Thunder Bay area."

"That can lead to locally poor air quality readings in those areas under the influence of the wildfire smoke," he said. "So it's almost a double whammy. We're getting the heat and humidity already from the the large scale weather system, but then adding to it with concerns locally, at least, of poor air quality readings due to wildfire smoke."

People with respiratory issues are particularly vulnerable to wildfire smoke

A Yellowknife emergency room physician is advising residents in the N.W.T. To regularly check the local air quality during wildfire season, and consider using face masks on especially smoky days. 

Dr. Courtney Howard, a Yellowknife emergency room physician, says that well-fitted N95 masks filter out about 90 per cent of fine particulate matter, making them far more effective than surgical masks. That's especially important when wildfire smoke can linger for days. 

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