Environment Canada is warning of possible thunderstorms on Wednesday followed by an extreme heat event on Canada Day weekend for parts of southwestern Ontario.
The special weather statement covers London, Komoka, Parkhill and Strathroy, as well as eastern and western Middlesex Counties.
Showers and thunderstorms are forecasted to begin overnight Tuesday and stretch into the following day. The weather agency said the strongest thunderstorm is expected to begin Wednesday morning and last through the midday.
Rainfall amounts could range from 30 to 50 millimetres. Higher amounts are expected for areas affected by heavier storms.
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Environment Canada added that a forecasted southwest flow will bring in hot and humid air from the Gulf of Mexico later this week.
As a result, daytime highs in the low- to mid-30s and humidex values reaching the mid-40s may begin either Friday or Saturday.
The heat will continue through the Canada Day long weekend and offer little relief, with lows only falling to the low-20s.
Environment Canada said this may be the most significant heat event of the season thus far. The weather agency does not yet know when it will end and have stated that it may continue into the middle of the following week.