It's getting cold in the North Star State. Really cold.
And the culprit is the counterclockwise movement of air surrounding the North Pole that snakes its way ever more south during the winter. You might know it as the polar vortex.
That pocket of cold, low-pressure air expands in the winter and contracts in the spring and summer, according to the National Weather Service. It's bordered by the jet stream, which moves from west to east between 5 and 7 miles above the Earth's surface.
"That really super-cold air can migrate quite a bit around the Northern Hemisphere," said Todd Krause, NWS Twin Cities' warning coordination meteorologist.
In December, Krause tracked a pocket of icy air in Siberia that reached 60 below Fahrenheit, or as cold as the most frigid temperature ever recorded in Minnesota. That was the low in Tower, just south of Lake Vermillion, on Feb. 2, 1996.
"Polar vortex" is a term scientists have long used to describe the conditions that keep both of the planet's poles in a state of perennial winter. But only in recent years has it become popularized, as reports of incredibly cold weather have increasingly made headlines. One particularly eye-popping example: In January 2014, temperatures in New York City plummeted 50 degrees in a single day.
Over much of the past decade, the wider public has taken to using "polar vortex" to describe any instance of unusually frosty weather.
"Technically, that's not what it is but it gets the message across," Krause said, adding he doesn't get too worked up by the now-colloquial use of the term. "When people hear 'polar vortex,' they associate that with incoming cold air, which helps them get prepared."
He'd much rather Minnesotans be prepared for icy temperatures than be a stickler about the term. That preparation means running errands before the air gets too chilly, and layering up before heading out the door.
