Environment Canada has issued a special weather statement for Sarnia-Lambton, warning of the potential for heavy thunderstorms and extreme heat.
The weather agency says there's the chance of thunderstorms on Wednesday followed by an extreme heat event for the Canada Day long weekend.
Showers and thunderstorms are forecast to affect Southwestern Ontario late overnight and Wednesday. The heaviest storms are expected early Wednesday morning through midday.
Total local rainfall amounts could be in the 30 to 50 mm range, with higher amounts possible under the heaviest storms.
A persistent southwest flow is then forecast to develop, bringing hot and humid air from the Gulf of Mexico.
Beginning Friday or Saturday and continuing through the Canada Day long weekend, expected daytime highs are in the low to mid-30s with humidex values into the mid 40's. Overnight low temperatures will only fall to the low 20s, 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.