The storm is expected to head out by evening, but some areas of northwest Indiana are expected to get hit with lake-effect snow tonight. Some places in Porter County could see half an inch of snow, the weather service said.



The first snow follows the first freeze of the season.



Temperatures dropped to 30 degrees at O'Hare International Airport this morning. Romeoville recorded a low of 25 degrees and Rochelle 23 degrees.



"We had a real chilly morning," said Matt Friedlein, a meteorologist with the weather service. "Very impressive for October."



Last year, no snow fell in Chicago until Nov. 12, when the city saw a dusting. The first measurable snowfall was not until Dec. 20.



The frigid air is being carried across Illinois by an "Alberta clipper," a low pressure system that originated over the Great Plains of Canada's Alberta Province. The center of the system is expected to cross central Illinois Tuesday evening, according to the Chicago Weather Center.



Looking ahead, far ahead, the Climate Prediction Center has updated its forecast for the winter. For Chicago, the center said there is an equal chance of winter being colder and snowier than normal or not as cold and not as snowy.



The Chicago Weather Center said that, "after crunching some numbers," this winter could see slightly less snow than average and be slightly warmer than average. The average yearly snowfall for Chicago over the last is 38.1 inches, and the average temperature for a Chicago winter--counted as from December through the end of February--is 26.4 degrees, according to the National Weather Service.