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Thursday's high is 20 degrees and low is -7, and Friday's high will be 4 degrees and low of -4. Wind chills Friday will push temperatures down to between -15 and -30 degrees.
With wind chills that cold, bundling up properly can be a matter of survival. Areas that are most susceptible like fingers, toes, the tip of the nose and the ears, should be covered in weather this cold. Temps this low can cause frostbite quickly.
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The Wind Chill Advisory is in effect from 6 p.m. Thursday until noon Friday for Cook, DuPage, Ford, Grundy, Iroquois, Kankakee, Livingston and Will counties in Illinois and Benton, Jasper, Lake, Newton and Porter counties in Indiana.
Metra is taking precautions for the cold, reducing trains' top speeds from 79 to 65 miles per hour. If temperatures drop below -10, officials said, speeds will be reduced further to 60 miles per hour.
Metra will also keep their trains running overnight so engines and cars are warm for early morning commuters.
Snow and ice is being cleared from the platforms as well.
Metra is asking commuters to take more time and leave more padding for their Friday commutes.
"Passengers can expect that there might be some delays because our schedules are very tightly timed, so if we are reducing speed to operate we're going to need more time to get down the tracks," said Metra spokesperson Meg Reile.
Some of the commuters that spoke with ABC7 said they're not even worried about extra time on their commute; they'll be working from home and staying indoors.
Polar Vortex Explainer: Get ready for bitter cold the next few weeks
A surge of arctic air is blasting into Chicago and the Midwest, starting this week and continuing into February. The Polar Vortex, which gained notoriety in 2014 when it brought shockingly cold temperatures to the Midwest, is a circulation of cold air in the Arctic Circle about 7 to 10 miles above ground in the stratosphere.
The vortex's strong circulation usually keeps it up above the North Pole, but when it weakens little pieces of energy break off and split, and send arctic air south.
The cold air then goes back to circling the North Pole in the summer.
The temps expected in the upper Midwest are even colder than in Chicago. The National Weather Service says the wind chill factor could dip to 40 to 50 degrees below zero (40 to 45 below zero, Celsius) in parts of Wisconsin and Minnesota and to 30 to 35 below (34 to 37 below, Celsius) in the Dakotas starting Thursday night.
Such wind chills, which describe the combined the effect of wind and cold temperatures on exposed skin, could cause frostbite within minutes.
The Associated Press contributed to this report.