On the last full day of summer, Environment Canada said conditions were favourable for the development of severe thunderstorms.
A severe thunderstorm watch was posted for Sarnia-Lambton Wednesday morning and elevated to a severe thunderstorm warning just after 11 a.m.
The warning was lifted at around 12:15 p.m., and the watches were taken down at around 3:30 p.m.
The agency said thunderstorms, heading east from lower Michigan, were capable of producing large hail and damaging winds.
Ping pong ball size hail and wind gusts of 90 to 100 kilometres per hour are possible.
Forecasters said there was uncertainty with respect to further thunderstorm development Wednesday afternoon.
Environment Canada said large hail can damage property and cause injury and strong wind gusts can toss loose objects, damage weak buildings, break branches off trees and overturn large vehicles.
The Office of the Fire Marshal and Emergency Management recommends that you take cover immediately if threatening weather approaches.
Fall arrives just after 9 p.m. Thursday.