It would be the third bout of freezing rain in as many weeks for London.
Environment Canada has issued a special weather statement for London-Middlesex and much of southern Ontario, noting that snow on Wednesday morning is expected to turn into freezing rain or drizzle in the afternoon.
The national weather agency notes that untreated surfaces may become icy and slippery and motorists are urged to drive according to the conditions.
Watches or warnings could be issued later on depending on how the system develops and how quickly the temperature rises.
The low-pressure system developing over the Southern Plains states is headed toward the Great Lakes, and rain is still possible into Thursday.
On Friday, the forecast is calling for sunshine and a high of 1 C but the weekend is expected to warm up to 3 C with the potential for rain or snow both Saturday and Sunday.