Environment Canada says a thunderstorm is expected to sweep across southwestern Ontario Monday.
The agency has issued a special weather statement for Guelph, Erin and Mount Forest.
They say heavy rain showers and thunderstorms could develop in the evening hours and continue into Tuesday night.
Those areas could get between 35 and 45 millimetres of rain.
Localized flooding is also possible in low-lying areas.
Others areas currently under a severe thunderstorm watch are Kitchener, Waterloo, Cambridge, Brantford, Woodstock, Stratford, Wingham, Listowel and Goderich.
They could also get thunderstorms capable of producing strong wind gusts and heavy rain.
