After a mild winter so far, polar vortex set to paralyze the Prairies

For the first six weeks of winter, the Prairies experienced very mild temperatures well above the seasonal norms, but that's all about to change.

A polar vortex is about to slide in — and the mercury is about to drop.

Environment and Climate Change Canada meteorologist Terri Lang says this is a very typical pattern for Saskatchewan in the winter.

"What is unusual is that we haven't seen this pattern very much this winter," she said. January was warmer than normal and had less snow, according to the weather agency's statistics.

A polar vortex occurs when the gap between the temperature in the Arctic and the temperature farther south begins to shrink. This weakens the jet stream, which makes it easier for cold air to move south.

This is what is currently happening, but with a twist: Not only is the jet stream weakening and allowing cold air to move south from Nunavut, but a Greenland high-pressure system will then intensify and draw mild air up along the back side of the polar vortex. This air will be brought up all the way from the Gulf of Mexico.

So while Saskatchewan freezes, Iqaluit will see a dramatic increase in temperature with daytime highs of –4 C (seasonal is –24 C).

How unusual is this?

"This backdoor front is not necessarily an unusual pattern for Iqaluit — what is unusual is how much warmth they have already experienced this winter so far," Lang said.

This dramatic temperature change started on Tuesday in the Northwest Territories, with temperatures plummeting to –40 C overnight, with wind chill values between –50 C and –60 C.

The big Prairie chill

As this system moves south, areas in northern Saskatchewan will start feeling its effects on Thursday, with overnight lows of –34 C, then –41 C on Friday. Extreme cold will touch areas such as Saskatoon by the weekend, with overnight temperatures hitting –37 C.

Parts of northern and central Saskatchewan should expect extreme cold warnings to be issued over the weekend. Extreme cold warnings are issued by Environment and Climate Change Canada when the temperature or wind chill is expected to reach –40 C for at least two hours. 

How long will this cold snap last?

"The cold air will be around for the better part of next week, with some gradual improvement by later in the week," Lang said.

The seasonal high for this time of year in northern Saskatchewan is –17 C. For central and southern Saskatchewan, normal is typically around –9 C.

Extreme cold puts everyone at risk. Anyone heading outside should cover up because frostbite can develop within minutes on exposed skin, especially with wind chill.