The weather agency received photographs and reports of high winds, and what appeared to be funnel clouds in Waterloo Region, said Geoff Coulson, a warning preparedness meteorologist.
"At this point, we're not quite sure if any of these funnel clouds actually had contact with the surface, which would make them full-fledged tornadoes, or if they did have contact with the surface if any appreciable damage occurred," Coulson said.
Coulson said a damage survey team would focus its efforts Monday in Grand Bend, where it is believed the storm originated, to investigate reports of downed trees and hydro poles. The team may then visit Waterloo Region to study the storm's path and determine if a tornado touched down.
"Fortunately the worst is over," said Coulson.
"The rain will be pulling out later today and we are looking at an improving situation weather-wise for the rest of the day."
Coulson said that for the rest of the week, southwestern Ontario will get cooler than normal temperatures, well below the seasonal average of 26 C.