Toronto could be in for stormy weather on Wednesday, Environment Canada says, and then things are going to get very, very hot.

As in, an "extreme heat warning" kind of hot, just in time for the long weekend.

The federal weather agency says there is "potential for heavy thunderstorms" today, with the most severe rainfall coming through the morning and into midday.

Most areas of the city will see between 30 and 50 mm of rain, but some pockets could get even more.

After the storm system passes, "a persistent southwest flow" will bring hot and humid air north from the Gulf of Mexico, according to Environment Canada. By Friday or Saturday, expect to see daytime highs into the mid-30s, though in some places it will feel more like somewhere in the mid-40s.

"This will likely be the most significant heat event of the season thus far," Environment Canada says in a special weather alert.

"Overnight low temperatures will only fall to the low twenties, providing little or no relief from the heat."

The agency adds that it remains unclear when the heat will break.

"Current indications suggest the heat could persist into the middle of next week."