Southwestern Ontario saw a blast of snow over the weekend and a cold front is now on its way.
An extreme cold warning was issued for Middlesex, Sarnia-Lambton, Chatham-Kent and Essex counties.
Temperatures as low as -18 C is expected Sunday evening into Monday.
This will be mixed with 30 kilometre an hour winds which will give wind chill values as cold as minus 30 C.
Environment Canada said risks will be greater for young children, older adults, people with chronic illnesses and those without proper shelter.
"Watch for cold related symptoms: shortness of breath, chest pain, muscle pain and weakness, numbness and colour change in fingers and toes," the agency said.
Environment Canada is also warning pets should also stay indoors.
The agency ended its warning for Essex County on Monday morning.
