DECATUR - A dense blanket of fog shrouded Central Illinois all day Monday and into the night, turning travel into a white-knuckle nightmare on many roads where visibility was a quarter mile or much less. Several injuries were reported.

However, much of the fog began to lift late Monday as thunderstorms moved through the area.

Police agencies reported dealing with dozens of accidents Monday as drivers groped their way through the murk. Many were said to be driving too fast and without lights and then skidded off roads slick with melting snow and ice.

Eight.;Stephen Decatur Middle School students were taken to Dr. John Warner Hospital in Clinton with minor injuries after a traffic accident involving a school bus occurred about 3:20 p.m. Monday. The crash at the intersection of U.S. 51 and Illinois 10 temporarily closed the intersection late Monday afternoon. Motorists were detoured to Illinois 54 east.

"I've never seen fog this thick," said Calvin Lunny of Clinton, who was at the scene before a detour was set up at the accident site. Lunny said the bus had gone off the road into a ditch and had heavy front-end damage.

Rick Imig, business manager for the Clinton School District, said police had called the district and asked for a school bus to use so the Decatur students could get home.

One woman driver, 8-months pregnant, was injured Monday afternoon when a semitruck plowed into the back of her car, shunting it into a cornfield at the intersection of Illinois 105 and Prairie View Road, between Decatur and Oakley. Both vehicles were westbound on 105 when the car slowed to turn south and was hit by the truck. The woman driver told police she had cuts to her head and hand, and pain in her right leg, but did not appear to be hurt seriously.

"Visibility out there was extremely low," said Macon County Sheriff's deputy, George Harris. "I'd say at that point in time it was down to 100 feet."

The National Weather Service issued a dense fog advisory as visibility levels shutdown and the Illinois State Police also reported dealing with multiple crashes throughout the area, most of them minor.

"If travel is required, be extremely cautious, especially as evening approaches," Master Sgt. John C. Wenzel said late Monday afternoon.

Chad Richards, a manager with Prairieland Towing in Decatur, said his company had been to some 50 wrecks by Monday afternoon. "We already had the bad snow and ice on the roads and the fog just doesn't help," Richards said. "We've got people running into the back of each other or they come up upon somebody too quick and they end up in the ditch."

The thick fog had smothered most of Illinois from early Monday, prompting officials to close Chicago's Midway Airport for much of the day and cancel hundreds of flights at O'Hare International while motorists struggled along state roads. The Bloomington airport canceled all but early morning flights.

In Coles County, fog contributed to three separate collisions within minutes Monday morning along Illinois 16 in front of Sarah Bush Lincoln Health Center. None of the drivers reported being injured, officials said.

The Shelby County Sheriff's Office reported almost a half-dozen accidents Monday morning and afternoon resulted from the thick fog. The most serious, a multi-vehicle accident involving a Shelby County Sheriff's Department squad car, sent five people from the Hillsboro area to the hospital.

Shelby County Deputy John Sanders was assisting at the scene of one of the collisions on Illinois 16 near the Dollville Road when a semitruck struck the rear of his squad car and another vehicle on the scene. Although no serious injuries were reported, five people were sent to Pana Community Hospital.

In Springfield, traffic lights were stuck on one color for long periods of time because sensors perched above some intersections could not see through the gloom to determine if vehicles were waiting.

Ernest Goetsch, the meteorologist in charge at the National Weather Service in Lincoln, said the heavy snow that hit the region last week had spawned the wall of fog. Goetsch said a steep rise in temperature - the mercury went from below freezing last week to the mid-50s Monday - evaporated vast quantities of snow-bound moisture into the air. Rain on Sunday only added to the mess.

"We aren't expecting there to be much improvement until midnight Monday, when we have a cold front coming in," added Goetsch. "Then we should see some improvement in the fog."

But it will be a mixed blessing. The cold front will herald showers and thunderstorms prompting a flood watch for Tuesday. "Then we're going to have some cooler temperatures and maybe have a mixture tomorrow night of rain and snow," Goetsch said. "It's going to be a busy period for the next couple of days."

The detailed forecast says Tuesday's thunderstorms "could be severe" before temperatures drop to around 30 Tuesday night with blustery winds to 25mph. Rain is expected to continue until around midnight and then be followed by a chance of snow, with any accumulation expected to amount to less than half an inch.

Tony Reid can be reached at treid@herald-review.com or 421-7977. The Associated Press contributed to this report.