Environment Canada has upgraded a thunderstorm watch to a severe thunderstorm warning for Waterloo Region, Guelph and surrounding areas.
A line of thunderstorms extending from Collingwood to just north of London appeared on Environment Canada's radar around 6 p.m. Thursday evening. These storms could produce large hail and wind gust around 70 km/h, says the weather agency.
The wet weather comes as scattered thunderstorms from northern Indiana and Michigan track into southern Ontario.
The agency warns people to take cover and avoid travel if they know severe weather is approaching.