Chicago weather: What is a polar vortex? How often does the weather phenomenon happen here? Experts explain.

Chicagoans are no strangers to cold weather, but some of the terminology used to describe frigid conditions can be confusing.

That’s why experts from the National Weather Service’s Chicago office — meteorologist Brett Borchardt and senior forecaster Matt Friedlein — answered a few common questions about extreme cold to provide some clarity. Their answers are listed below.

Why does cold weather always seem to sneak up on us?

“Like the past few years, our start to winter has been relatively tame with mild stretches and limited snow,” Borchardt said. “The reality of living in Chicago is the snow and cold will come eventually whether we like it or not!”

What exactly is a polar vortex?

Borchardt and Friedlein: “A polar vortex is a large low pressure system that is accompanied by arctic cold air that typically originates near the North Pole. Since the systems are so large, they typically take a long time to move across the country leading to a prolonged period of cold weather. As a result, polar vortices are often accompanied by periods of snow, blustery wind, and generally unpleasant weather.”

What makes it different from just very cold weather?

Borchardt and Friedlein: “While the term polar vortex gained notoriety after bone-chilly cold outbreaks of January 2014 and late January 2019, most cold outbreaks are associated with polar vortices. It is fairly normal to have polar vortices surge south into the United States during the wintertime months especially behind winter storms. The combination of cold, polar air and a fresh snowpack is what typically leads to our coldest days and nights.”

Do you know how many times we’ve experienced polar vortex conditions in the past, say, 10 years?

Borchardt and Friedlein: “We typically experience polar vortices every winter, though most are not nearly as cold as the ones we remember most. It seems we have to deal with a bad polar vortex once every five to 10 years, though that’s an anecdotal measure. Polar vortices, at least those that are the most unpleasant, typically occur within the time frame of late December to early February.”

Memorable recent weather events with polar vortex conditions

Jan. 30-31, 2019

Chicago observed its coldest temperatures in 34 years, minus 23 degrees on Jan. 30, 2019, and minus 21 degrees on Jan. 31, 2019, at O’Hare International Airport, the city’s official recording site. Both are among the Top 10 coldest ever in the city.

The lowest temperature ever recorded in Illinois was observed on Jan. 31, 2019, when Mount Carroll (west of Chicago in the state’s northwest pocket) checked in at -38 degrees.

Chicago’s coldest recorded temperatures and longest stretches of deep freezes

Why the polar vortex gripped Chicago in 2019 — and why you may see more of it

From Jan. 30, 2019: Parts of Siberia, Mars and the South Pole all will be warmer than Chicago this week

Some hardy Chicagoans brave the polar vortex to get to work, help others: ‘We just have to buckle down and do our jobs’

Stunning photos capture Chicago’s beauty during the polar vortex

Frozen Chicagoans take to Twitter to vent about #Chiberia

Nara Schoenberg: The polar vortex was Chicago’s common enemy. And I miss it.

Jan. 5-7, 2014

Chicago earned the nickname “Chiberia” with temperatures plummeting to minus 16 degrees, which was 30-40 degrees below normal. Winter 2013-14 was the third coldest and snowiest winter on record here.

Tribune photographers capture “Chiberia”

Polar vortex, polar pig and other weird ways to describe this weather

Mary Schmich: Chicago winter of 2014 — when it was OK to stay home

From March 9, 2014: 26 died from cold this year