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What is a heat wave?

An official heat wave is usually rare
An official heat wave is usually rare

Staff writers

June 19, 2012 — When temperatures soar, the phrase “heat wave” comes to mind, but what is a heat wave exactly?

How do you beat the heat?
How do you beat the heat?

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.

Extreme heat can be very dangerous
Extreme heat can be very dangerous

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 however, it's important to know how to recognize the signs of heat-related illness. With heat exhaustion a person is going to present like they're in shock -- cold, wet skin, confused and anxious, maybe nausea or vomiting. Heat stroke is more serious and can cause permanent brain damage and even death.

If you suspect someone is suffering from a heat-related illness, call 911 and focus on cooling the victim down.

Intense prolonged heat can also affect air quality and UV readings. Stay on top of conditions in your area by checking your local forecast.

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