LONDON, ONT. -- Wednesday could be the hottest day of the summer as Southern Ontario continues to bake under a hot air mass.

A heat warning has been in effect for a week, with daytime highs climbing between 30C and 33C over the last seven days.

The high on Wednesday is forecast to reach 35C with a humidex of 41.

The record for July 8, 36.4C was set back in 1988.

The strong high pressure ridge will persist across the lower Great Lakes allowing the intense heat to hold until Friday.

An air quality advisory was issued Tuesday for London-Middlesex, Elgin, Lambton, Essex, Huron and Perth counties, with moderate to poor air quality expected nto Wednesday.

Elevated ozone levels are expected to occur in the late afternoon and early evening. Many people are at risk, especially those with lung diseases such as asthma and COPD.

If you are planning to exercise or work outdoors, there is an increased risk to the health effects due to air pollution, you can use the AQHI to plan ahead.

Drought-like conditions will continue, with only the slight risk for pop-up showers for the rest of the week.

London’s last rainfall recorded at London International Airport was on June 27, when 7.2 mm of rain fell.

An upper trough moves east across Ontario this weekend, allowing a cold front to drop southeast across the lower Great Lakes Friday evening into Saturday.

This will break the heat and bring some much needed rainfall, and showers are in the forecast Saturday and Sunday.