SCARED HAPPY: Sydney Miller, 7, screams as she sleds  down a hill near the intersection of Vernon and First streets in Madison on Saturday. Temperatures warmed over the weekend, making it perfect for sledding and other fun in the snow. That all changes tonight when temperatures will plummet to below zero. (Staff photo by Ken Ritchie/kritchie@madisoncourier.com)
SCARED HAPPY: Sydney Miller, 7, screams as she sleds down a hill near the intersection of Vernon and First streets in Madison on Saturday. Temperatures warmed over the weekend, making it perfect for sledding and other fun in the snow. That all changes tonight when temperatures will plummet to below zero. (Staff photo by Ken Ritchie/kritchie@madisoncourier.com)
Another round of arctic air is expected to push into the Ohio River Valley tonight and send the wind chill below zero.

The National Weather Service issued wind chill warnings for portions of Indiana, saying values could reach 45 below zero in northwestern Indiana and approach 40 below elsewhere in northern and central Indiana tonight.

Locally, temperatures tonight are expected to drop to about 7 below zero. Wind chill readings will make it feel like 9 below to 19 below zero.

Tuesday's high temperature in Madison is expected to be 9 degrees with a windchill of 4 below.

There will be a slight warming trend toward the middle and end of the week. Wednesday's high is expected to be around 20, and highs Thursday and Friday should reach into the low 30s.

There is only a slight chance of snow through the end of the week.

Indianapolis Mayor Greg Ballard urged residents of the state's largest city to gas up their vehicles and stock up on food Sunday before the bitter cold arrived.

"Due to extreme temps, I encourage schools, biz & organizations to delay opening Monday at minimum.

Safety of anyone outside is top concern," Ballard tweeted.

Among the weather-related closures, Valparaiso University in northwestern Indiana canceled classes for today and Tuesday.

Even before the chill set in, motorists in northern Indiana had to contend with a few more inches of fresh snow and blustery winds blowing snow across roads and lowering visibilities.

A 15-mile stretch of Interstate 65 in White County and Interstates 80/94 in Lake County had numerous slide-offs, spin-outs, jackknifed semitrailers and other crashes, Indiana State Police Sgt. Ann Wojas said Sunday.

"Staying off the interstate entirely is the safest option. Use alternate routes," Wojas said.

Seven central and northern Indiana counties - Steuben, Fulton, Wabash, Huntington, Tipton, Jay and Randolph - limited travel Sunday to emergency management workers only, the Indiana Department of Homeland Security said on its website. More than 40 other counties, including Jefferson, recommended only essential travel.

The Madison County Highway Department reported snowdrifts higher than 10 feet Saturday in some areas of the county northeast of Indianapolis.

National Weather Service Meteorologist Scott Blair stopped short of calling the latest round of cold part of the polar vortex, a system of winds that circulate around the North Pole.

"There's really nothing abnormal about the air that's coming into the area," he said. "It's just been a very persistent pattern" of cold air.

Blair said it's an amplified pattern of the jet stream, with cold air filtering in behind a large trough of low pressure. Simplifying, he explained:

"Troughs are typically associated with unstable or unsettled weather, and, at this time of the year, much colder air."