Toronto has once again issued an extreme cold weather alert for the second time this week as frigid temperatures are expected on Friday.

Today’s high is set to be -6 C in Toronto but will feel like -18 C with the wind chill, according to Environment Canada.

The national weather agency cautions that today’s weather conditions pose a risk for frostbite.

In anticipation of the cold weather forecast for the next 24 hours, Toronto’s Medical Officer of Health issued an Extreme Cold Weather Alert Friday morning. The alert will stay in effect until further notice.

Today’s alert follows one that was issued by the city on Monday when the temperature felt like -20 C with the wind chill.

Extreme cold weather alerts are typically issued when temperatures are forecast to reach -15 C or colder, or when the wind chill is forecast to reach -20 C or colder. Other weather-related factors may also be considered.

The city says its warming centres will remain open at 129 Peter St., 5800 Yonge St. and at the Exhibition Place, Better Living Centre at 195 Princes’ Blvd.

A fourth warming centre will also open today at 7 p.m. at 1684 Queen Street East.

Warming centres usually stay open until noon on the day an alert is terminated.