Environment Canada says anyone with plans to be on the roads Sunday evening into early Monday morning needs to be extremely cautious.
A fog advisory has been issued for most of Southern Ontario including the GTA as the massive warm-up in temperatures combined with the moisture in the area could lead to near zero-visibility at times.
The weather agency says travel could be hazardous, most likely around midnight when fog becomes more widespread.
It's expected to burn off Monday morning with only patchy fog remaining into Monday afternoon.
The city of Toronto is one of the few locations that is not currently under the advisory.