After a refreshing weekend in southern Ontario, the heat will return with a punch this week just as summer officially begins.
An unusually strong, sprawling ridge of high pressure south of the border will be responsible for trapping some of the hottest temperatures and humidex values so far this year, and on record for some.
Temperatures reaching the low and mid-30s and humidex values into the 40s will dominate as the week progresses, with no relief in sight for the foreseeable future.
On Monday, extreme heat will make its way to northwestern Ontario and the extreme southwest with daytime highs reaching the low 30s. This progression of heat will continue into the middle of the week and will reach the Greater Toronto Area (GTA).
As well, an advancing warm front will bring the risk of showers and thunderstorms to parts of northeastern Ontario and cottage country on Monday, and perhaps a spotty shower for parts of the Golden Horseshoe in the evening.
While the chance of thunderstorms remains in the forecast, the risk is very scattered in nature.
Humidex values will be in the high 30s and low 40s by Tuesday. Even Timmins, Ont., will be feeling like 44 on Tuesday – tying its all-time record that was set on July 1, 1963.
For areas near the Great Lakes, wind direction will determine how hot it gets.
Although Sault Ste. Marie is usually sheltered from extreme heat by three Great Lakes, the city will experience an ideal wind direction from the Michigan Upper Peninsula on Tuesday that will send the humidex up to 41 before crashing to 19 on Wednesday.
Similar conditions are expected throughout the week and could even persist into next weekend.
Stay tuned to The Weather Network for the latest forecast updates for Ontario.