The City of Toronto is under an extreme cold weather alert as temperatures are expected to dip to -16 C overnight.

On Friday morning, it was -9 C in the city, but with the wind chill, Environment Canada said it felt more like -20.

The national weather agency forecasted that the temperature will fall to -11 C late Friday morning, then will hover around that temperature until sunset.

When it gets dark, the temperature will drop to -16 C. In addition to the dipping mercury, strong northwest winds are blowing across the Toronto area, with gusts reaching up to 50 km/h.

The Medical Officer for Health calls an extreme cold weather alert when Environment Canada forecasts temperatures will reach -15 C or colder. Alerts are also issued at warmer temperatures if the forecast includes factors that increase the possible impact on health including wind chill factor, precipitation, or several consecutive days and nights of cold temperatures.

Extreme cold weather alerts were also called on Jan. 7, 9, 10, 12, 13, 14, 16, 20, 25 and 27. Friday marked the city's 11th alert this winter.

Based on the data from the last ten years, the city calls an average of 16 alerts per year.

During cold weather alerts, Toronto Medical Officer David McKeown advises residents to check up on loved ones and those who may be particularly vulnerable.

Groups at risk of frostnip and frostbite, hypothermia, and worsening heart conditions include the elderly, infants, people with pre-existing heart or respiratory conditions and the homeless.

To stay warm, those who live in the city should dress in layers covering all exposed skin, stay dry, seek shelter, and avoid drinking alcohol.