Light snow that began falling overnight was expected to intensify somewhat Wednesday afternoon.
That prompted Environment Canada to issue a special weather statement that included Sarnia-Lambton.
The weather agency said total snowfall accumulations of about 10 centimetres, four inches, were likely by Wednesday evening.
Motorists were being urged to exercise caution and adjust to changing road conditions.
The special weather statement was ended for Sarnia-Lambton at around 4 p.m.