Heat dome brings extreme weather to North America

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.

Millions of Canadians are under heat alerts as conditions persist. Environment and Climate Change Canada has issued heat warnings for parts of Ontario, Quebec, the Prairies and the Northwest Territories, where daytime highs and humidity have climbed well above seasonal norms.

Ontario remains one of the hardest-hit provinces, with residents in eastern Ontario urged to limit outdoor activities during the hottest hours of the day. Authorities also advised people to stay hydrated, avoid strenuous outdoor activities, and regularly check on vulnerable groups, including older adults, young children and those sensitive to extreme temperatures.

The combination of sweltering heat and unstable atmospheric conditions has also heightened the risk of severe thunderstorms. In Ottawa, Canada Day celebrations were disrupted on Wednesday after heavy storms and localized flooding forced the cancellation of afternoon programming, including a flypast by the Snowbirds demonstration team.

Elsewhere, torrential rain in Manitoba's Parkland region caused severe flooding, prompting the city of Dauphin to declare a local state of emergency on Wednesday.

In the United States, multiday warnings of extreme heat were issued for New York, Boston and Philadelphia ahead of Fourth of July celebrations. Temperatures were forecast to reach 38 C in the Northeast, with the heat index even higher because of humidity, the US National Weather Service said.

A heat dome has been smothering a vast area from the US Midwest to the East Coast, intensifying temperatures and worsening heat stress across multiple states. Meteorologists warned that such systems can persist for several days, limiting nighttime cooling and amplifying health risks for vulnerable groups.

Experts warned that the combination of high temperatures and humidity could pose serious health risks. In Hamptonburgh, New York, air conditioning failed on a bus carrying Junior ROTC cadets, resulting in multiple heat-related illnesses. New York City said more than 200 teams of government workers and volunteers would check on homeless people, while hundreds of cooling centers would be available across the city.

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