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Large parts of Ontario – including some northern regions – were under heat warnings on Tuesday as temperatures soared.

Environment Canada issued warnings for a stretch of the province from Prescott and Russell to Windsor, with temperatures expected to reach or surpass 30 C. The humidex could make it feel as hot as 40 C in some areas.

In northern Ontario, heat warnings were in place in the Greater Sudbury Area, North Bay, Sault Ste Marie and Elliot Lake. Other areas, including Thunder Bay and Kenora, were under severe thunderstorm watches.

The weather agency said some parts of southern Ontario could see the heat linger for as long as five days, though many will see some relief by Thursday.

Several cities urged residents to try beating the heat by drinking plenty of water even before feeling thirsty, staying in the shade, going to air-conditioned places, wearing breathable, light-coloured clothing and rescheduling outdoor exercise for cooler parts of the day.

Residents were also encouraged to check in with friends, family and neighbours living alone, as well as those at high risk, such as older adults, young children and people with chronic illnesses.

Communities also warned residents to watch for symptoms of heat illness, including dizziness or fainting, nausea or vomiting, headaches, extreme thirst, fast breathing and very dark yellow urine.

In Toronto, the city extended the hours of seven pools until 11:45 p.m. Tuesday in light of the heat warning.

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