MADISON, Wis. -- Nearly a half-foot of snow has fallen in some parts of southern Wisconsin on Wednesday and several inches more are expected as a major winter storm sweeps through the state, WISC-TV reported.

The storm is already making travel difficult by clogging the roads with snow and creating at times, near-whiteout conditions.

The National Weather Service said that much snow accumulation is expected southeast of a line from Dubuque, Iowa, to Evansville to Jefferson to West Bend to Sheboygan.

The bulk of the snow was expected to fall through Wednesday morning, then gradually decreasing from west to east Wednesday afternoon. The NWS issued a winter storm warning for about 31 counties in Wisconsin, Iowa and Illinois from Tuesday afternoon until Wednesday afternoon.

Nine inches of snow was forecast for Chicago, where airlines canceled about 1,000 flights at O'Hare International Airport by midday and about 50 flights at Midway Airport, said Karen Pride, spokeswoman for the city's aviation department. Remaining flights had 45-minute delays, she said.

NWS meteorologists said visibility will probably drop to below one-quarter mile at the height of the storm, and roads in an east-west direction will experience considerable drifting.

A driver was killed on a slick interstate in Milwaukee County on Wednesday when he apparently lost control of his car and skidded in front of a tractor-trailer.

The sheriff's department said that the 51-year-old man died at the scene. The driver of the semi tried to brake, but wasn't able to avoid the crash.

The heavy snow is coming in waves with a round of heavy snow.

The snow will continue into Wednesday night, but will lighten as time goes on. An additional inch or less of snow is possible, Smith said. The skies will become mostly cloudy overnight. The nighttime low should dip to about 15 degrees.

The winter storm is also causing a number of cancellations at the Dane County Regional Airport. Airport operations and maintenance crews pulled an all-nighter, clearing the runways, taxiways and gate areas, WISC-TV reported.

Airport officials said that they advise travelers to call ahead to check their flight's status.

The Rock County airport is open, and workers are doing everything they can to keep the runways clear. Driver Chet Waldhart is one of the plow drivers working on Wednesday and he said that he got a few hours of sleep at work Tuesday night before going back out to plow.

The snow is wetter than expected and it's creating icy conditions, he said.