A winter storm is predicted to dump up to a foot of snow on the suburbs through noon today.

National Weather Service meteorologists first issued a winter storm warning from Thursday night through 9 p.m. Friday, with heavy snow making travel "very difficult to impossible." Late Thursday night the warning was shortened so that it now lasts only until noon.

More than 200 flights were canceled "proactively" at O'Hare International Airport, the Chicago Department of Aviation reported, and more than 70 at Midway.

Metra's BNSF Line will run 84 instead of 94 trains Friday in an effort to reduce switching operations. Heavy ice and snow can cause switching problems and subsequent delays. To learn more, go to metrarail.com.

Pace bus service is warning riders to take transit only for essential trips from Thursday night through Sunday and postpone nonessential travel. "Significant delays due to heavy snow and hazardous driving conditions," are expected, officials said.

Suburban school districts began announcing closings for Friday, including all schools in Elgin Area School District U-46, Hawthorn District 73, Wheaton Warrenville Unit District 200, Naperville Unit District 203, Palatine-Schaumburg High School District 211, Northwest Suburban High School District 214, Barrington Area Unit District 220 and Community Unit District 300. Plus day care centers, senior centers and other businesses are not opening Friday morning, the Emergency Closing Center is reporting.

Go to emergencyclosingcenter.com for a complete roundup of closings.

Various suburbs are reminding residents that cars should not be parked on streets so snow plows can sweep through. Many suburban governments have announced village or city halls will not be open on Friday.

The Circuit Court of Cook County also said it will close Friday. "There will be no court in session in any Cook County courthouse and that the Office of the Clerk of the Circuit Court will be closed," except for Central Bond Court at the Leighton Criminal Court Building in Chicago, Chief Judge Timothy Evans said in a statement. All cases set for Friday will be rescheduled.

The storm warning includes all of northern Illinois and northwest Indiana. Six to 12 inches of accumulation is possible. The weather service is warning of significant reductions in visibility at times.

"If you must travel, keep an extra flashlight, food and water in your vehicle in case of an emergency," the weather service said in a statement.

The snow will add on to the three inches that have fallen over the past three days.

The Illinois Tollway announced it is deploying its fleet of nearly 200 snowplows to combat the expected snowfall, and the Illinois Department of Transportation warned travelers to avoid driving through Friday night. Officials said snowy and icy roads are expected to cause low visibility and significant delay.

For those who have no choice but to brave the snow, officials recommended driving with extreme caution and preparing for the worst by keeping a full tank of gas and cold weather essentials such as blankets, food and water and an ice scraper in the car.

• Daily Herald correspondent Christopher Hacker contributed to this report.