Environment Canada says dangerous thunderstorms are possible late Friday afternoon and into the evening hours.
A severe thunderstorm watch was issued for Sarnia-Lambton and surrounding area at mid-afternoon.
The national weather agency said storms may be capable of producing damaging wind gusts of up to 110 km/h and heavy rain.
Utility outages are possible.
Emergency Management Ontario recommends that you take cover immediately if threatening weather approaches by taking cover in a basement or interior room.
If outside, protect yourself from flying debris and hail and secure all loose objects.
We're reminded that heavy rain can cause flash flooding and significant reductions to visibility.
Strong wind gusts can damage trees, buildings and overturn vehicles.