Consider celebrating Valentine's Day indoors today, as Environment Canada has issued a cold weather alert for Toronto, warning of a "prolonged period of very cold wind chills."

The temperature is set to reach a low of - 20 C Saturday night, but it will feel much colder with the wind chill.

"Bitterly cold arctic air will be ushered in by stiff northerly winds today and tonight," the alert said. "As a result, wind chills will easily reach minus 40 to minus 35 tonight into Sunday."

Periods of snow are set to end by early Saturday afternoon, and Saturday night will be mainly cloudy with a 60 per cent chance of flurries, the weather agency said.

Environment Canada warns that people heading outdoors should exercise extreme caution, as exposed skin may experience frostbite in just a few minutes.