Environment Canada has issued a weather advisory for the Hamilton area because of conditions "favourable for the development of funnel clouds" near the shores of Lake Erie and Lake Ontario.
The agency says funnel clouds have been reported in the areas near near Wheatley and Leamington, near the western shoreline of Lake Erie.
Environment Canada says: "These types of funnel clouds are generated by weak rotation under rapidly growing clouds or weak thunderstorms. This weak rotation is normally not a danger near the ground. However, there is a chance that this rotation could intensify and become a weak landspout tornado."
The advisory will be upgraded to a watch or warning is conditions change.
It adds that these kinf of landspouts do not typically lead to significant damage, but " can still be dangerous." They can knock down trees, damage roofs or blow debris around.
"Treat any funnel cloud sighting seriously," it advises. "Should a funnel cloud develop nearby, prepare to take shelter. These funnel clouds usually appear with little or no warning."
If you see a funnel cloud or want to make a report os severe weather, email Environment Canada at firstname.lastname@example.org or tweet with the hashtag #ONStorm.