OTTAWA/NEW YORK — A destructive "heat dome" is bringing extreme heat to parts of North America, including large areas of Canada and the northeastern United States, while severe storms and torrential rain have caused flooding in Canada ahead of Canada Day and US Independence Day celebrations.

As parts of southern Ontario, Quebec and the eastern United States swelter through a heat dome, here are the health warning signs to watch out for — and how to keep cool.

Heat domes trap overnight temperatures too — and millions without air conditioning are facing this week's Eastern U.S. heat wave.