Environment Canada is warning Waterloo-Wellington, Huron-Perth and southern portions of Bruce-Grey to be on the lookout for severe storms that could produce tornadoes.
A tornado watch was issued for those areas, as well as regions to the north around Newmarket, Uxbridge, Caledon, Dufferin County, Barrie, Collingwood and Lindsay, at 2:23 p.m. Tuesday.
According to Environment Canada, severe storms will develop rapidly over that portion of the province Tuesday afternoon.
Strong winds and large hail are expected to come with the storms, while conditions exist to potentially produce tornadoes.
The tornado watch is less severe than a tornado warning, which is issued when a tornado is imminent, rather than possible.
A severe thunderstorm warning is also in place for Grey-Bruce as well as areas near Barrie, Collingwood and Midland, while parts of southern Ontario not covered by either that or the tornado watch are under severe thunderstorm watches.
Earlier in the day, Guelph, Wellington County and areas to the north were under severe thunderstorm warnings due to a system that moved out of the area before noon.
Environment Canada says anyone caught in a tornado or other severe storm should take cover immediately.
The risk of thunderstorms in southern Ontario is expected to continue into Wednesday.