Environment Canada expanded its forecast Tuesday for a heat wave across most of Alberta.
It now includes Calgary and surrounding areas, as well as the southeastern portion of the province.
The heat wave is expected to begin Wednesday and last until Friday.
"Daytime highs ranging between 28 to 35 C and overnight lows between 13 to 18 C can be expected," the agency said in a special weather advisory issued Tuesday morning.
High temperatures in both Calgary and Edmonton are forecast to reach or exceed 29 C.
These areas are now under a heat warning:
Airdrie - Cochrane - Olds - Sundre.
Bonnyville - St. Paul - Cold Lake - Lac La Biche.
Brooks - Strathmore - Vulcan.
Cardston - Fort Macleod - Magrath.
City of Calgary.
City of Edmonton - St. Albert - Sherwood Park.
Cypress Hills Provincial Park - Foremost.
Drayton Valley - Devon - Rimbey - Pigeon Lake.
Drumheller - Three Hills.
Fort McMurray - Fort McKay.
Fort Saskatchewan - Vegreville - Redwater - Smoky Lake.
Hanna - Coronation - Oyen.
Kananaskis - Canmore.
Leduc - Camrose - Wetaskiwin - Tofield.
Lloydminster - Wainwright - Vermilion - Provost.
Medicine Hat - Bow Island - Suffield.
Okotoks - High River - Claresholm.
Peace River - Fairview - High Prairie - Manning.
Red Deer - Ponoka - Innisfail - Stettler.
Spruce Grove - Morinville - Mayerthorpe - Evansburg.
Wabasca - Peerless Lake - Gift Lake - Cadotte Lake.
Westlock - Barrhead - Athabasca.
Heat warnings are issued when the temperature is expected to pose an elevated risk of heat-related illnesses, such as heat stroke or heat exhaustion.
People in areas under a heat warning are advised to take precautions, including rescheduling outdoor activities to cooler times of day, drinking plenty of water and taking frequent breaks from the heat in cooled indoor spaces, where possible.
"Do not leave any person or pet inside a closed vehicle, for any length of time," Environment Canada also advised.
It's also important, the agency said, to watch out for people who are especially vulnerable to the heat.
This includes "infants, children, seniors and individuals with pre-existing lung, heart, kidney, nervous system, mental health or diabetic conditions, outdoor workers, as well as those who are socially isolated."
Symptoms of heat stroke or heat exhaustion include high body temperature, a lack of sweat, confusion, fainting and unconsciousness.
Alberta Health Services provides more heat-related health advice here.