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The coldest blast of arctic air this winter sent wind-chill readings to 50 below zero in Minnesota — and the pain is headed south and east for Thursday, where kids in some of the U.S.'s biggest cities are getting a day off from school.

Forecasters say the wind chill could plunge to 31 below in Chicago, 21 below in Boston and 7 below in New York on Thursday morning. It will be below zero as far south as Tennessee and in the teens in New Orleans and Jacksonville, Florida.

In all, The Weather Channel reported, 190 million Americans will be under wind chill watches or warnings Wednesday or Thursday.

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The real temperatures won't look much better: The forecast low for Louisville, Kentucky, on Thursday is zero, or 24 degrees colder than normal. For Atlanta, it's 13 degrees. In Nashville, Tennessee, where the coldest air temperature recorded this fall and winter has been 18 degrees, the forecast low for Thursday morning is 5 degrees.

It's easily the worst blast of cold since the infamous polar vortex a year ago. There's more snow in the forecast, too, mostly around the Great Lakes. Parts of Michigan could get a foot through Friday, and a foot and a half could fall outside Syracuse, New York.

The Buffalo area — where a massive snowstorm led to record flooding that killed 13 people in November — could get as much as 16 inches of new snow, forecasters say.

Public school systems in several major cities announced that classes are canceled Thursday, including those in:

Boston

Chicago

Cleveland

Columbus, Ohio

Indianapolis

Milwaukee

Providence, Rhode Island

Some relief is on the horizon, as The Weather Channel said temperatures should be closer to normal by the weekend, although New York may not see the freezing mark again until Sunday.

SOCIAL

Forecast #WindChill will be -31° in #Chicago & in the single digits across much of the #Southeast Thursday morning. pic.twitter.com/G0prAq8XcH — The Weather Channel (@weatherchannel) January 7, 2015

Apparently when it's 20 below in Chicago, many residents walk around in disguise ....@mikebettes @weatherchannel pic.twitter.com/oUj1O2prl9 — Trish Ragsdale (@Trishrags) January 7, 2015

— Erin McClam