There were numerous cold weather school closing days last year in Chicago.
"How Much Snow Does It Take To Close Schools?
January 30, 2014 10:45 AM
"The Chicago Public School system has only closed four times since 1999–two days that year after a post-New Year’s Day blizzard and two days after the blizzard of 2011. In those cases, there was more than 20 inches of snow on the ground.
CPS has closed four times this month for extreme cold weather, but not snow"
http://chicago.cbslocal.com/2014/01/30/how-much-snow-does-it-take-to-close-schools/