Environment Canada has issued a special weather statement for the London area with the possibility of funnel clouds forming.
At 4:30 p.m. the weather agency issued a weather advisory for London, Parkhill, Strathroy, Komoka, and west and east Middlesex County.
The statement said conditions are favourable to generate weak rotation under rapidly-growing clouds or weak thunderstorms.
The weak rotation is normally not a danger near the ground but the weather agency said there is a chance it could intensify and become a weak landspout tornado.
If conditions become more favourable for a tornado, Environment Canada will issue watches and warnings.
Landspout tornadoes do not usually cause significant damage but can still be dangerous, toppling trees, damaging roofs or tossing debris short distances.
Environment Canada is advising everyone to treat all funnel clouds seriously and to take shelter if one forms.
Funnel clouds usually appear with little or no warning.