A cold front settled into the region Sunday and is expected to hang around throughout the week.
Environment Canada forecasts daytime highs of around -14 for most of southwestern Ontario.
"The coldest days are Monday and Tuesday, Wednesday is still going to be cold but slowly we'll be exiting out of it," said Environment Canada Meteorologist Gerald Cheng. "I just want to remind everybody that there is still a lot of winter ahead of us."
Cheng said there will be dangerously low temperatures overnight.
"If we focus on the overnight lows, early morning hours, those are really, really cold conditions reaching almost -20 degrees with wind chill values close to -30," said Cheng.
The average high for this time of year is around -1 Celsius.