The City of Toronto is under its 19th extreme cold alert of the year, with temperatures expected to dip to -23 C by Thursday night.

The alert was called Thursday morning by the city's Chief Medical Officer of Health David McKeown.

It was just -9 C at the time of the decision, but Environment Canada forecasts the temperature will fall steadily through the day, reaching a low of -23 overnight. With the wind chill, it's expected to feel more like -30.

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. So far this month, alerts have been called Feb. 1, 2, 3, 4, 5, 8 and 9.

Based on data from the city, an average of 16 alerts are called each winter.

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.

As a result of the forecast, Environment Canada has issued its own extreme cold weather warnings for parts of southern Ontario.

Warnings are in effect for the following areas:

  • Algonquin
  • Bancroft-Bon Echo Park
  • Barrie-Orillia-Midland
  • Belleville-Quinte-Northumberland
  • Burk's Falls-Bayfield Inlet
  • Cornwall-Morrisburg
  • Dufferin-Innisfil
  • Dunnville-Caledonia-Haldimand
  • Elgin
  • Grey-Bruce
  • Haliburton
  • Halton-Peel
  • Hamilton
  • Huron-Peel
  • Kingston-Price Edward
  • London-Middlesex
  • Niagara
  • Oxford-Brant
  • Parry Sound-Muskoka
  • Peterborough-Kawartha Lakes
  • Renfrew-Pembroke-Barry's Bay
  • Sarnia-Lambton
  • Simcoe-Delhi-Norfolk
  • Smiths Falls-Lanark-Sharbot Lake
  • Stirling-Tweed-Frontenac
  • Toronto
  • Waterloo-Wellington
  • Windsor-Essex-Chatham-Kent
  • York-Durham