There are strong storms in some areas north of Gatineau and a heat warning south of the city.
The agency has severe thunderstorm warnings Wednesday afternoon covering a strip of land around Gatineau and as far north as Maniwaki.
Environment Canada warns the thunderstorm could produce strong winds, large hail and heavy rain.
Severe thunderstorm watches are issued when conditions are likely to produce storms like that. They are upgraded to warnings when one of those weather elements becomes more certain.
It also issued a heat warning Wednesday afternoon for Ottawa and communities as far south as Gananoque, west as the Perth area and east to the Quebec border.
The dangerous heat is expected to hit Thursday, last through Friday and potentially affect the weekend.
People could see daytime temperatures reach 30 or 32 C, with humidex values near 40, Environment Canada said. Nighttime lows could stay above 20 C.
Extreme heat can pose significant health risks to everyone, but certain groups are particularly vulnerable. These include older adults, infants and young children, pregnant people and those with physical or mental health conditions.
Ottawa Public Health offers an interactive map of places to stay cool throughout the city, including pools, libraries, splash pads and community centres, plus fountains. Other health authorities and municipalities have shared similar maps.
Everyone is being asked to avoid exercising during peak heat times, staying inside where possible — especially in spaces that are being cooled — and drinking plenty of fluids.