A blizzard of special effects

The filmmakers call the sequence the Big Freeze. In director Roland Emmerich’s big-budget action epic “The Day After Tomorrow,” which comes out May 28, global warming sets off a chain of devastating tornadoes, floods and earthquakes. But even in a movie littered with eye-popping computer-generated special effects sequences, the most impressive one involves a gigantic frozen hurricane that sweeps into New York.

Action begins at the tip of the Empire State Building. Ice crystals begin creeping earthward, the cold exploding the building’s windows. A helicopter freezes in midair. The eye of the supercooled hurricane, called the Super Cell in the movie, is a vortex of snow that freezes -- and kills -- everything in its path. Surveying the destruction moving across Manhattan, the camera locates one of the film’s stars, Jake Gyllenhaal, as he retreats into the Metropolitan Museum of Art for warmth.

From start to finish, “The Day After Tomorrow” took 12 special effects companies two years and more than $100 million to complete. “If the audience is taken out of the film for one moment -- ‘Oh God, that looks cheesy’ -- we’re lost,” explains the film’s visual effects supervisor, Karen Goulekas. “We’ve lost the story.”

Extensive snowstorm research began in May 2002. From there, the filmmakers spent three months photographing and surveying midtown New York in excruciating detail, using technology originally engineered by the U.S. military to create a three-dimensional model of the city. “Every window, door and molding is in extremely high resolution,” Goulekas says. “Then we could plot the camera moves.”

The next challenge was making the digital Big Freeze look real. “It always comes down to photorealism,” the supervisor says. “How opaque should ice be? How fast should it come on? You find that to cover the whole city immediately makes it look like a miniature.”

The filmmakers were still working frantically on postproduction in April. “You don’t ever finish visual effects shots,” Goulekas says. “You just run out of time.”