The first heat warning of the summer has been issued by Environment Canada.

The warning covers Ottawa, Gatineau, and areas around Brockville, Prescott-Russell, Kemptville, and Cornwall.

It warns of daytime highs above 30 degrees Wednesday through Friday, and humidex values approaching 40.

The current forecast for Ottawa calls for a high of 31°C Wednesday, with a humidex of 34. Thursday’s forecast high is 32°C with a humidex of 36. Nighttime lows will also be relatively high, with temperatures around 20°C. The average temperature for this time of the year is around 26°C. A cold front Friday night will bring temperatures back in line with the average.

Other parts of eastern Ontario are under a special weather statement, also advising of daytime highs around 30, but with a bit more relief at night.

Environment Canada says heat warnings are issued when very high temperature or humidity conditions are expected to pose an elevated risk of heat illnesses, such as heat stroke or heat exhaustion. Young children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors are at greater risk from the heat.