The film was originally scripted with Sam and his friends as 11-year-olds, but director/screenwriter Roland Emmerich changed them to high school students for Jake Gyllenhaal, who Emmerich had seen in October Sky (1999). Emmerich asked "Can Jake Gyllenhaal play a 17-year-old?"
20th Century Fox invited a group of scientists to preview the film, to test their reactions to the science used in the film. None of the scientists were impressed with what they saw, although most conceded that the movie was enjoyable nonsense.
The consultation by NASA scientists was requested before the filming of the movie, but NASA stated that the events in the film were too ridiculous to actually occur, and hence denied the request. NASA sent a memo out to all of its employees stating that they were not allowed to comment on the likelihood of the events portrayed, but later rescinded this restriction.
South Park (1997) creators Matt Stone and Trey Parker managed to get their hands on a copy of this film's script during its pre-production. The two planned to secretly shoot the same film with puppets instead of actors, word for word, and release it on the same day. The duo abandoned these plans after their lawyer convinced them that such a film would never get released.
The US Army loaned several UH-60 Blackhawk helicopters for the rescue scene at the end, prompting the Canadian authorities to reassure the people of Montreal that they weren't being invaded by the USA.
There was some doubts among the production team about having a major disaster hit New York, especially after 9/11. Ironically, that sensitivity did not appear to be shared by New Yorkers themselves. Whenever it played in the Big Apple, audiences whooped with delight when the city gets hit by an enormous tidal wave.
Roland Emmerich confided that the Statue of Liberty would be turned over by the force of the massive amount of water flowing around it but said he wanted to create a symbol of American values that stood up to the forces.
The casting of Kenneth Welsh as the Vice President was controversial, due to his physical resemblance to then-US Vice-President Dick Cheney. However, Roland Emmerich insisted on it for that very reason, admitting that the characters of the President and Vice-President were intended to be criticism of the Bush/Cheney administration's opposition to the Kyoto Protocol for reducing greenhouse gas emissions.
The Red Cross put up several stands at theaters in the U.S. featuring pamphlets with information on what to do to keep safe during tornados, floods, and blizzards for concerned people who had just viewed the film.
The opening weekend gross of this film, along with the second weekend gross of Shrek 2 (2004), represented the most money ever earned in a single weekend in movie history at that point. This has since been passed and is now the 5th highest grossing weekend ever.
Two library-bound survivors ask whether they should burn the works of Friedrich Nietzsche, whose "The Antichrist" states in its preface: "Only the day after tomorrow belongs to me. Some are born posthumously." Part of this line provided this movie's title.
While speaking to fans in Denver, director Roland Emmerich said he became interested in doing a movie involving weather while shooting The Patriot (2000). He said his whole day revolved around what the weather forecast was in order to shoot the outdoor scenes and that he really just wanted to control the weather himself. "The Coming Global Superstorm", a non-fiction novel by Art Bell and Whitley Strieber, was used for reference. Emmerich concedes that while the events portrayed in the film are indeed possible, the time frame over which they take place was implausibly short and tailored for sheer entertainment value. In keeping with the movie's ecological theme, Emmerich paid $200,000 from his own pocket to make the production "carbon-neutral" - the first of its kind in Hollywood - all carbon dioxide emitted by the production was offset by the planting of trees, and investments in renewable energy.
The footage of the plane that crashed in the Midwest before the FAA's flight ban is actually a stock photo of a January 1990 Avianca Airlines crash on Long Island. The hurricane footage is of Hurricane Iniki (1992) in Hawaii. It was shot by Roland Emmerich's assistant Aaron Boyd, who renamed the storm "Hurricane Noelani" after his Hawaiian wife. The UK blizzard footage is from a January 2002 report.
The building used as the United States Embassy in Mexico was actually the Centro Vida/Life Center Ministries and private school in El Paso, Texas. Mexico is visible from the building, which is on Glory Road near the University. The church and school later moved, vacating the building. The Mexico-United States "bridge" is really an overpass in El Paso which overlooks Mexico in a dramatic way. El Paso's real bridges don't look like that, and security is much stricter with fences and Border Patrol agents. When these scenes were being filmed, local residents were concerned about military-style helicopters landing and flying low over residential neighborhoods, and the streets closed by the filming. Some called the authorities out of fear.
When the camera pulls away from the Earth after the astronaut exclaims "the air is so clear" the image of the Earth is a modified version of the "Blue Marble" picture created by Robert Simmon. The Blue Marble picture is actually a fake comprised of thousands of satellite photos and some of the clouds are duplicated. The Apple iPhone uses the Blue Marble picture as the default wallpaper.
The Manchester United player who is seen scoring is Dutch striker Ruud van Nistelrooy. It was a friendly game against Boca Juniors of Argentina which took place on 10 August 2002 and whose final score was Manchester United 2 Boca Juniors 0.
In the tornado sequence, the janitor is listening to a football match in his headphones. The match he is listening to is Argentina Vs. Peru and the guy commenting the match is Victor Hugo Morales, a famous Argentinian commentator of football matches.
The movie had a subplot involving Rick Hoffman that was mostly cut out of the film, where Hoffman and his two friends were unethical businessmen who were working on an illegal securities trading plan with a Japanese colleague. The Japanese man is still shown being struck and killed by mega-hail falling during the ice storm siege, but footage of him talking to Hoffman's character about how they needed to steal money to avoid going to prison was edited out. This explains why Hoffman and his friends are introduced during the massive wave destruction in New York City and appear to be unlikable characters before they're demolished by the water (and their bus is later crushed by the freighter ship), since they had unused footage establishing them as bad guys.
When Sam calls his father to tell him the sewer has backed up into the school, Dunst can be seen standing behind Sam near his elbow, her sweater pulled up over her nose and mouth (although in very poor light)
When the L.A. weather forecaster looks out the window of the forecast center you can see the reflection of the tornado approaching. This same technique is also visible in the Emmerich film 2012 (2009) when the pyroclastic cloud is seen in the reflection of the glass door as it approaches the airport in Las Vegas.