During the Chicago blackout, the observation deck of the John Hancock Center still has glowing green lights on.
When Mitch's wife confronts him about cheating he is holding his plate of dinner in one hand and a glass in the other. In the next shot of him the plate and glass switched hands.
When the car is getting a flat tire when they meet up with the airplane, the first shot the car has a flat tire, yet when Mitch starts to change the tire it is suddenly not flat anymore.
When they arrive to meet the plane at the abandoned military airfield, the tarmac is dry and has a heat shimmer as the plane lands, yet they are only in the eye of the storm, so everything should be wet.
In the shopping mall, a store's sign can be seen clearly lit during a blackout.
When power is restored to the mall, the escalators start up. Modern escalators do not start up on their own after a power cut. They have to be manually reset. This is a safety feature.
It is stated that the strongest winds ever recorded in a tornado were 243mph. However, a tornado in Moore, Oklahoma in 1999 (this movie was made in 2004) had Doppler Radar windspeeds recorded at 318mph.
There are several points when the final storms hit Chicago that although the scenes are in places being hit there is obvious sunshine on actors and surrounding buildings. While it is true that with some storms you can have severe weather happening close by while you have sunshine overhead, considering the severity of the storms portrayed here it seems highly unlikely there would be any sunshine where the storms collided.
When the lights go out at Wrigley Field, play could not have been affected, since it was a day game, and the lights would not have been on.
When the elevated train is given a sudden red signal and slams on the brakes, the camera shot shows freight car trucks braking rather than passenger trucks.
During the first storm that hits Chicago, you can still the same tornado formation graphic that was seen as the tornadoes were forming over Las Vegas.
When Oceanic 762 makes an emergency landing at O'Hare, all preparations are made for a crash landing however on descent, we see that the passengers are still sitting upright in their seats, not in a crash position.
The two women in the elevator are struck from above by debris larger than the openings on the metal grating forming the elevator's ceiling.
One of the pilots calls "three in the green", indicating all three landing gears show down and locked, while the sound of the gear descending can still be heard. The landing gear indicators would not turn green while the gear is still in motion.
During the first storm at the Benson home when Lindsay arrives home, you can clearly see the actor's mark on the rug.
When Tornado Tommy is speaking to the Japanese man on the phone, his sunglasses reflect the image of the film crew.
As the storm batters Chicago, we see a montage of storm shots. There are palm trees in at least two of these shots.
In the shopping mall, there is a sign for the Bay in the background. The Bay is a Canadian department store chain, and at the time of filming, did not have any locations in the United States.
During one scene at the National Severe Storms Lab, one technician reports a tornado has touched down outside Braxton Missouri and is headed straight towards St. Louis. However, there is no such town as Braxton, MO.
When Jane calls Mitch and tells him to get Lindsay from the police, she tells him that she's being held at "...the Old Town precinct station." Chicago does not have police precincts; instead, there are area divisions subdivided into 25 districts. The districts do have names (although there is no Old Town district) but local people are just as likely to refer to them by number.
In her first appearance, Amy Harkin identifies her location as "...the fountain outside city hall...". She is standing in front of Buckingham Fountain, which is in Grant Park at the intersection of Columbus Drive and Congress Parkway, thirteen blocks from city hall. There are, in fact, no fountains at or adjacent to city hall.
In category 7, it is reveled that when the thermal plume from the city collides with a chunk of falling mesosphere, the storms happen. This can be stopped and cause the storms to end if the electricity is gone. Chicago didn't have electricity when the storms hit.
Amy Harkin consistently mispronounces the names of a number of Chicago landmarks and street names.