The showers and thunderstorms forecast for Wednesday are forecast to give way to a persistent southwest flow, bringing hot and humid air from the Gulf of Mexico to Southern Ontario. Beginning Friday or Saturday and continuing through the Canada Day long weekend, expected daytime highs are in the low to mid thirties with humidex values into the mid forties. Overnight low temperatures will only fall to the low twenties, providing little or no relief from the heat.
There is still uncertainty regarding when the heat event will come to an end. Current indications suggest the heat could persist into the middle of next week.
This will likely be the most significant heat event of the season thus far. Heat warnings will be issued as the event draws nearer.