Environment Canada issued an advisory Thursday saying there's the chance of funnel clouds forming.
The weather agency says scattered thunderstorms are expected in the afternoon and early evening across southern Ontario.
Dime-sized hail, wind gusts to 70 km/h and frequent lightning are possible and funnel clouds could also make a brief appearance in the unseasonably cool and unstable air mass.
The advisory says funnel clouds are generated by weak rotation under rapidly growing clouds or weak thunderstorms and are not normally a danger near the ground, but the rotation could intensify and become a weak landspout tornado.
The public is advised to treat any funnel cloud sighting seriously and to take shelter if one develops nearby. They usually appear with little or no warning.
