Environment Canada has issued a severe thunderstorm watch for a wide swath of central Ontario.
The weather agency says severe thunderstorms capable of producing heavy rain are possible from early this afternoon to late evening.
The watch covers areas just outside of Toronto, including York, Durham, Halton and Peel Regions, as well as Orangeville, Innisfil, Barrie, Orillia and Midland.
It also covers areas east of Toronto, including Peterborough, Kawartha Lakes, Haliburton, Bancroft and South Frontenac and in the southwest, Waterloo Region and Wellington and Perth Counties.
The agency says residents of those areas should be prepared for severe weather and are advised to take cover immediately if threatening weather approaches.
The warning comes one week after a tornado touched down in Angus, Ont., damaging 100 houses.