The Greater Montreal area is under a heat warning Monday as Environment and Climate Change Canada states a warm and humid air mass could lead to a humidex value of 40.

That number could rise to 43 in more densely populated areas, creating especially uncomfortable conditions.

“Health risks are greater for older adults, infants and young children, pregnant people, people with physical and/or mental illnesses and people with disabilities or mobility issues,” the agency notes. “Drink plenty of water regularly, even before you feel thirsty, to decrease your risk of dehydration.”

Environment Canada stresses that thirst is not a good indicator of dehydration.

“If you are in an overheated area, seek a cool place such as a tree-shaded area, splash pad, misting station, or air-conditioned spot like a public building,” it continues.

Early signs of heat illness include feeling unwell, fatigue, thirst and headache.

“These can rapidly evolve into life-threatening emergencies,” Environment Canada states. “Move to a cooler environment immediately, such as a shaded or air-conditioned space.”

Heat warnings are issued when very high temperatures or humidity could elevate the risk of heat stroke or heat exhaustion.

There is also a severe thunderstorm watch for the Mont-Laurier area as “conditions are favourable for the development of dangerous thunderstorms capable of producing very strong wind gusts, large hail and heavy rain this afternoon and evening.”