Brace yourself for another round of bitterly cold air in Kitchener-Waterloo starting late on Thursday, Environment Canada says.

The weather agency has issued an extreme cold warning for Thursday evening, continuing until Sunday morning.

The statement applies to Waterloo region, Guelph and all of Wellington County.

Geoff Coulson, warning preparedness meteorologist for Environment Canada, based in Toronto, says it is time to bundle up.

An adult and child skate at Kitchener City Hall on Wednesday. Environment Canada says another cold snap is coming and it means windchill values of –30 on Thursday and Friday nights. (Kate Bueckert/CBC) "Unfortunately, starting on Thursday and into Saturday, we are expecting a fresh shot of very cold Arctic air," he said.

"This will likely lead to extreme cold warnings having to be issued for the Kitchener-Waterloo area for Thursday night into Friday morning, and again Friday night into Saturday morning," he added.

"People should be taking precautions and dressing accordingly, if they are going to be spending any time outside."

Environment Canada said a bitterly cold northwesterly flow of air will develop over Southern Ontario on Thursday. Extreme cold warnings will likely be issued, given that the criteria for southwestern Ontario is windchill values of –40 or colder.

Cold snap to ease by Sunday

The cold snap will ease by Sunday, when a southwesterly flow of air is expected to develop.

​The high for Thursday is forecast to be –13 C while the low is expected to be –25 C, with a windchill value of –40 or colder. Winds are expected to gust up to 50 km/h.

"Temperatures and wind chill values will be slightly lower Friday night," the extreme cold warning said.

The high for Friday is forecast to be –21 C while the low is expected to be –23 C, with a windchill value of –40 or colder.

On Saturday, the forecast is calling for a high of –15 C and a low of –20 C. The windchill value on Saturday is expected to be around -–30 C.

Coulson said the temperature will be more seasonal on Sunday and Monday. Normal high for this time of year is – 3 C.

Geoff Coulson, warning preparedness meteorologist for Environment Canada, based in Toronto, says limit time outside to stay warm. (Submitted by @JoeSzalai via Twitter)

Act accordingly

Limit time outside and wear layers and wearing good boots, mittens and a hat to keep extremities warm, he advised.

"We've been dealing with this since Boxing Day, but this is a fresh surge of Arctic air coming down for Thursday to Saturday," Coulson said.

Meanwhile, Wellington-Dufferin-Guelph Public Health is also reminding residents that more extreme cold weather is on the way.

The risk of frostbite rises when the windchill value is –30 or colder and prolonged exposure to extreme cold can result in hypothermia, it said in a news release on Wednesday.

Vulnerable people could be at risk

"Temperatures are going to be extremely low, and vulnerable family members including infants and the elderly could be at risk. Watch the weather reports and prepare for extreme cold," said Dr. Nicola Mercer, medical officer of health and CEO of Wellington-Dufferin-Guelph Public Health.

Residents are urged to check in with vulnerable family members and neighbours to make sure they are safe.