The base camp (where the crew trucks and equipment are staged) for the end sequence was at a pig farm down the road from the well-house. Every morning the cast and crew were greeted by the smell of a 2-acre pig-waste holding pond in the middle of all the trucks.
According to urban legend, a tornado hit a drive-in theater in Stoney Creek, Ontario, while this movie was playing. In reality, a tornado hit a drive-in theater in Thorold, Ontario, on May 20, 1996, damaging a screen. The movie was not playing when the tornado hit, but it was scheduled to play that evening.
The real town of Wakita, Oklahoma had part of its old downtown area demolished by the film crew for the scenes after the twister passes. The studio then paid for the downtown to be rebuilt. The town also kept the new fire truck used in the film.
(at around 1h 9 mins) The characters are alarmed when TV screens go blank, showing only static, before the tornado hits. In the days before digital TV, it was discovered that tornadoes generate a signal that will override and blank channel 2 on TV sets. Digital TVs do not react that way.
In order to get the background skies looking suitably stormy, the truck cab sequences had to be flooded with high-intensity lighting for contrast. As a result, Helen Hunt and Bill Paxton suffered minor retinal burns through much of the filming.
In an early scene when Philip Seymour Hoffman is sitting on a lawn chair, he lifts his leg in the air while laughing. His genitals were fully visible for a split second. It was edited out of the DVD and VHS releases, but it was leaked from VHS screeners sent to industry professionals.
(at around 58 mins) Jan de Bont said he regretted thinking of the hail sequence because it took so long to do and was very difficult. Also the crew couldn't find ice blocks big enough in Oklahoma for the hail making machine. They ended up having to find them in other states and some were obtained from the Burlington Ice Company in Burlington, Iowa. The ice blocks were made special by pouring milk in with the water, so the hail would show up better on film.
Many of the news reports spread throughout the movie are actual weathermen from Oklahoma news stations, including Gary England, chief meteorologist at KWTV in Oklahoma City, and Rick Mitchell, chief meteorologist at KOCO in Oklahoma City. The "1969" footage of Gary England giving the televised tornado warning to Jo's family is actual archived footage of him issuing a tornado warning; however, Gary England did not join KWTV until 1972.
(at around 53 mins) After the team leaves Wakita, there is a seemingly impossible helicopter shot in which the camera descends several hundred feet in a matter of seconds, ending up mere feet from the convoy. This was achieved by having the cars drive slower than usual and then speeding up the film.
Trailers contain a shot not in the film: a truck tire hurtling towards the viewer. This was supposedly one of the test shots that was created during pre-production to prove that CGI was capable of executing the effects sequences with the necessary level of realism.
Jonas is vilified for selling out to 'corporate sponsors', which is ironic considering Pepsi's very prominent product placement. When the team is making the 'wings' for the sensors, all of the cans are Pepsi products. In almost all the shots showing the 'Doppler', the colors spiral inward and morph into the Pepsi symbol.
The laptops used in the film are Silicon Graphics Indy Presenter LCD screens (not real laptops) that have been modified to look like functional laptops when in fact the screen image is generated by a computer off-screen.
(at around 1h 14 mins) Lois Smith's character is reading Dante Alighieri's Inferno when the twister hits Wakita. The book also features a tornado in the second circle of Hell that punishes people ruled by Lust.
(at around 1h 30 mins) The name on the tanker truck that pushes Bill's pickup off of the tree is "Benthic Petroleum" which is the same oil company that Ed Harris' crew works for in The Abyss (1989). Ed Harris majored in theater at the University of Oklahoma where the National Severe Storms Laboratory is located.
The original Director of Photography was Don Burgess (best known for his collaborations with Robert Zemeckis), but he and many other crewmembers walked off the set midway through filming after a series of heated arguments with director Jan de Bont.
Although Amblin Entertainment has collaborated with both Warner Bros. and Universal on many occasions (Amblin co-founder Steven Spielberg directed films for both studios), as of 2014, this film marks the only time Amblin collaborated with both studios on the same film.
(at around 59 mins) As one of the characters looks at the screen of their weather computer, he screams "That's no moon, it's a space station!" That's Obi-Wan Kenobi's line when he, Luke, Han, and Chewbacca first discover the Death Star.
Bill's truck goes from being a 1996 Dodge Ram 1500 club cab long box to being a 1996 Dodge Ram 2500 club cab long box. Though both look similar the wheel hub caps give it away by going from 5 lug wheels to 8 lug.
Tom Hanks was the original choice for the role of Bill Harding. Hanks even briefly accepted the role and read lines with the cast before dropping out. Kurt Russell and Bill Paxton were also in consideration for the role.
Six of the top 10 billed actors either starred or co-starred in 1 or more 80s cult classics. Helen Hunt-Girls Just Want To Have Fun, Project X, Peggy Sue Got Married, Next Of Kin Bill Paxton-Weird Science, Stripes, The Terminator, Next of Kin (played Helen Hunt's bro-n-law Cary Elwes-The Princess Bride, Glory Jami Gertz-The Lost Boys, Less Than Zero, Sixteen Candles, Crossroads Alan Ruck-Ferris Bueller's Day Off, Bad Boys (w Sean Penn) Todd Field-Gross Anatomy
The unique siren sound made by Dorothy is achieved by combining the sounds created by a standard police, fire, ambulance siren control head. These control heads have modes called yelp, siren, and phaser. This same sound would later be heard during the chase scene from Terminator 3: Rise of the Machines (2003), with the fire truck, crane, ambulance, police cars, all chasing the Toyota Tundra. In the latter movie the sound was created accidentally. In this movie on purpose.
The trivia items below may give away important plot points.
at around 1h 40 mins) At the end of the movie Bill remarks that the tornado didn't take the house. In fact, it was originally supposed to. The Hardin County, Iowa, Historical Society and many citizens objected to the house being blown up so it was spared. The area is now a tourist attraction as the rubble from the barn and fences is still there exactly as it was in the movie.
There is a lot of speculation the Bill and Jo could not have survived being in the F-5 tornado at the end of the movie. While this would be true if the tornado was still at F-5 strength, as the tornado dissipated shortly after it hit them, the winds may have already been greatly reduced and the debris cloud lessened. So theoretically if that was the situation they could have survived as depicted.
at around 1h 14 mins) In the scene right before aunt Meg's house gets hit by the tornado you can see a movie playing on her TV and the actress you see is Judy Garland, who plays Dorothy in the The Wizard of Oz (1939).