Police said the rushing water swept a 60-year-old man underneath his car.
Bystanders and paramedics were able to pull him out, but he later died in hospital.
We did have a fatality, said Brian McAsey, a spokesman for the Calgary Fire Department. A person was driving and there was a lot of moving water around their vehicle. The person was on a major thoroughfare, but nonetheless, they got outside their vehicle for inspection.
“Unfortunately, although we were able to rescue them quickly, the person had gone into cardiac arrest.
The storm dumped heavy rain and hail over the city. Water was so deep in some areas, cars were submerged up to their headlights.
Police received more than 100 calls for assistance during the deluge, including 62 reports of flooding, five house fires and three water rescues.
It was a very busy and intense two hours in which, of course, extreme weather played a great role, said McAsey.
The same system caused severe thunderstorms to pop up in southern Saskatchewan Saturday, battering some areas with thick hail and damaging winds.
To stay on top of current conditions in your area, watch The Weather Network on TV. Local forecasts come up every 10 minutes on the 10s. You can also subscribe to receive weather warnings and public alerts on your mobile phone.
With files from Sana Ahmed & the Canadian Press