A snowfall warning is in effect for Windsor-Essex, Sarnia-Lambton, Chatham-Kent, London-Middlesex, Elgin, Oxford and Brant counties.
The warnings stretches north into Huron-Perth and Grey-Bruce and east to Niagara, including the city of Hamilton.
Widespread winter weather is affecting all of southern Ontario, with snowfall warnings and a weather advisory for the GTA.
All school vehicles were cancelled Wednesday in Middlesex, Elgin, Oxford County, Huron-Perth and Red Zone.
A steady snow will continue this evening and overnight, with the heaviest snow expected closest to Lake Erie. The snow will quickly accumulate making travel hazardous in the region.

Snowfall amounts will climb between 20 and 30 cm. Blowing snow will also be a factor Wednesday evening with winds gusting out of the north.
The temperatures will drop tonight and snow-covered roads will turn icy across the region.
The main area of snow will ease southward, dropping stateside Thursday morning, but a second upper wave will bring the potential for light snowfall near Lake Erie Thursday afternoon.
Skies will clear Friday as high pressure builds and southern Ontario will get a break from the snow, but the icy cold persists. Temperatures will be below normal right through the weekend.