Environment Canada is warning Londoners of up to 50 mm of rainfall Saturday afternoon and evening.
Meteorologists say showers and thunderstorms will be very slow moving and some areas may receive more rainfall.
In addition to the heavy rainfall, Environment Canada also says funnel clouds may develop.
They’re generated by weak rotation under rapidly growing clouds or weak thunderstorms.
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Meteorologists say they’re not a danger near the ground, however, the rotations could intensify and become a weak landspout tornado, which can be strong enough to topple trees, damage roofs or toss debris.
Saturday calls for a high of 26 C and a low of 16 C.