At one point Hydro Ottawa reported 8,600 customers had lost power in communities including Gloucester, Goulbourn, Kanata and Nepean as a result of power lines brought down by the storm. As of 8 p.m. ET that number had been reduced to 2,500 customers.
Hydro One reported thousands of homes in an area stretching to Alexandria and Cornwall in the east from Barry's Bay south of Algonquin Park in the west had been affected by outages
The largest of these outages, in an area encompassing Renfrew and Calabogie, saw power cut to about 5,600 homes in the region. Service had only been partially restored as of 8 p.m. ET.
Ottawa airport, which had cancelled or delayed arriving and departing flights during the storm, reopened just after 7 p.m. ET.
Unconfirmed tornado near Golden Lake
The federal weather agency had issued tornado warnings for several eastern Ontario communities west of Ottawa, including Smiths Falls, Lanark, Sharbot Lake, Barry's Bay, Killaloe, Renfrew, Arnprior, Calabogie and French River.
Ottawa and regions to the east remain under a severe thunderstorm warning into Monday evening.
The weather agency said there have been unconfirmed reports of a tornado touching down near Golden Lake about 140 kilometres west of Ottawa.
Campers at a trailer park near Lake Doré, close to where the unconfirmed tornado was sighted, say they are shaken up after heavy rains and winds hit at about 2:30 p.m.
Trailer park hit by storm
No injuries have been reported, but trees fell on several trailers at the Lake Doré Tent & Trailer Park, owner Carol Brisebois told CBC News.
"We could see some trees falling down, lots of damage to trailers, awnings, trees and boats lifted from the shoreline. I had one of my fishing boats, my row boat, went flying," Brisebois said.
Emergency Management Ontario recommends taking cover immediately when threatening weather approaches.
Last Tuesday, two tornadoes touched down in eastern Ontario after a similar group of storms rolled through the region.
One hit the area of Athens, near Brockville, and another touched down around Summerstown, east of Cornwall.