Chris Scott, a meteorologist at The Weather Network, says although the term gets thrown around a lot during long stretches of summer heat, a true heat wave must meet certain criteria.
A heat wave is defined as three or more consecutive days with temperatures above 32°C. Quebec has a slightly lower threshold, with a heat wave defined as three or more days with temperatures over 30°C.
These parameters mean actual heat waves are fairly rare, Scott says.
“Quite often, we'll get a string of hot days, but one of them has a maximum temperature just under 32°C, which negates the official heat wave,” he explains. “It's much easier to get three consecutive days above 30°C in southern parts of the country.”
Heat waves occur when the jet stream rides far to the north, creating a large ridge of high pressure to the south. The sinking air within that high pressure system warms and produces high temperatures and clear skies over a wide area.
When that pattern lasts for a few days, a heat wave is born.
When heat waves do occur, the results can be devastating.
For two weeks beginning on July 5, 1936, much of North America sweltered through the deadliest heat wave in history. All-time temperature records were shattered in Ontario and Manitoba.
The heat twisted steel rail lines, buckled sidewalks and baked fruit on trees.
More than 1,000 Canadians died in the heat wave; in the U.S., the death toll was a staggering 5,000.
Health risks of heat waves
Heat waves pose two major health risks: heat exhaustion and heat stroke. Both can be avoided by minimizing your exposure to extreme heat, says Robyn Ashby, a spokesman for St. John Ambulance.
However, it's important to know how to recognize the signs of heat-related illness.
“With heat exhaustion, (the patient) is going to present like they're in shock -- cold, wet skin, confused and anxious, maybe nausea or vomiting,” he says.
Heat stroke is more serious and can cause permanent brain damage and even death. It presents with similar symptoms to heat exhaustion, with one major difference: the patient will be hot and dry to the touch.
If you suspect someone is suffering from a heat-related illness, call 911 and focus on cooling the victim down, Ashby says.
“Immediately get them out of direct sunlight ... and start to circulate some cool water over their body.”
The best ways to prevent heat-related illness include staying hydrated, avoiding exertion and staying in the shade, or better yet, indoors.
When extreme heat is forecast, most cities will issue heat alerts, which activate public cooling centres in places like malls and libraries.
Intense prolonged heat can also affect air quality and UV readings. Stay on top of conditions in your area by checking your local forecast on The Weather Network; they come up on TV every 10 minutes on the 10s.