Bundle up, Toronto – or better yet, stay the heck inside. It's going to be a cold one tonight.

Toronto Public Health has issued an extreme cold weather alert, effective immediately and until further notice, across the city, based information from Environment Canada.

The federal weather authority forecasts a low of -11 degrees Celsius overnight on Tuesday, but with sharp northwest winds gusting up to 50 km/h.

With the wind chill, it's expected to feel more like -20 degrees Celsius tonight.

NEWS RELEASE: Extreme Cold Weather Alert Issued – seek shelter, check on loved ones. More info: https://t.co/XJ1hMzIZZb

— Toronto PublicHealth (@TOPublicHealth) December 12, 2017

As per the city's public health policies, an extreme cold weather alert must be issued in Toronto when the temperature is forecast to reach -15 degrees Celsius or colder, or when the wind chill is forecast to reach -20.

This is to activate additional city resources that help keep vulnerable people safe during periods of extreme cold; resources such as more shelter beds, overnight street outreach, and the relaxation of service restrictions for community agencies.

"The City asks that residents help vulnerable people by calling 311 if there is a need for street outreach assistance," writes the city. "Call 911 if the situation is an emergency."