CHICAGO (CBS) — A deep freeze will be settling over the Chicago area starting Thursday evening, and you’re best advised to bundle up.

Temperatures aren’t exactly warm on Thursday. As of just after 10 a.m., the official air temperature for Chicago was 18 degrees, and wind chills have been hovering in the single digits.

But compared with the conditions coming overnight, 18 degrees will seem like beach weather.

CBS 2’s Megan Glaros says the overnight low is expected to drop to 1 degree below zero in the immediate Chicago area, and between minus 5 and minus 7 degrees farther west.

But the wind chills will drag the temperature down even further, to make it feel as if it were between minus 20 and minus 30.

A wind chill advisory will be in effect for the entire Chicago area from 9 p.m. Thursday until 11 a.m. Friday, as the Arctic air blows into the area in the form of winds of 15 to 25 mph.

As WBBM Newsradio 780’s Bob Roberts reports, city officials urged Chicago residents to be smart about the frigid weather.

Deputy Health Commissioner Julie Morita said smart Chicagoans will put off any unnecessary trip outside until the weather moderates over the weekend.

“Let it wait,” Morita said. “Limit the time you spend outside.”

LISTEN: Newsradio 780’s Regine Schlesinger Reports

Morita said temperatures in recent days might have lulled some Chicagoans into complacency, but said the below-zero temperatures expected demand respect.

“Wear several layers of loose, warm clothing,” she said. “Pay special attention to keeping your head, hands, ears and feet warm. Wear a hat, a scarf, gloves, socks and winter boots. And stay dry, because moisture can defeat the warm effects of your clothing.”

On Friday, the weather will be sunny and pleasant, if you’re looking out the window in a well-insulated room. If you’re outside, get out your heavy winter coat. The forecast high for Friday is a mere 9 degrees, with wind chills as low as 20 below zero.

Landlords are required to heat buildings to 68 degrees by day and 66 at night. Those needing to get out of the cold can get warm at libraries, police stations and most other public buildings; the city’s Family and Support Services Center at 6 South Kedzie is open around the clock, and hundreds of extra shelter beds were available last night. To get a ride to a warming center or shelter, find the nearest shelter or report someone in need of shelter, call 311.

When kickoff comes for the Bears-Packers NFC Championship Game, look for the temperature to be back up at 20 degrees with a few light flurries.

Watch & Listen LIVE