Environment Canada has issued a heat warning for much of southern Ontario with humidex values of 40 expected over the next several days.
The weather agency issued the alert for most regions stretching from Windsor up to eastern areas of the province.
The alert said daytime temperatures in the high 20s to low 30s are expected Wednesday and Thursday and will come with humidex values near 40 each day.
The weather agency said the hot weather may extend into Friday and again the humidex could reach 40.
Overnight temperatures will be above 20 each night and will “provide little relief from the heat,” the alert read.
Temperatures are expected to cool off sometime Friday or on the weekend, although Environment Canada indicated the Ottawa area may see earlier relief from the heat.
Officials said the hot conditions could cause the Air Quality Health Index to approach the high-risk category.
Thunderstorms are also a possibility in some areas.