A large sphere, 6 feet in diameter, is suspended over tables and chairs in the five-story lobby of the National Weather Center complex on the University of Oklahoma campus in Norman. Swirling on the globe's surface are bursts of white clouds and angry-looking purple storms, constantly moving and changing. That's the world's weather, happening right now. It's one of the many cool things about the nation's weather mecca, which you can tour for free.

THE BASICS

The National Weather Center didn't exist until 2006. Two things helped bring it about. The first was the movie "Twister," which boosted student interest in meteorology. The second was the catastrophic 1999 tornado that devastated Moore, just south of Norman.

Within these walls, the weather is forecast, researched, taught and applied to private business, agriculture and everything that weather affects -- which is pretty much everything.

The tour takes about 90 minutes, the length depending on how many people in your group want to tell their own storm stories. Everybody has one, and the guides -- University of Oklahoma meteorology students -- are happy to hear them.

"There is no other place like this on the planet," says Kevin Kloesel, director of the Oklahoma Climate Survey and associate dean of the university's College of Atmosphere and Geographic Sciences, which is housed in the building.

THE TOUR

During the tour, you'll see that offices are arranged in a circle around a central open space, and the walls are glass so that students and others can see what scientists are doing. For example, you can see into the Weather Prediction Center, the room where experts study the national and global weather. Monitors display weather patterns, storms, trends, all sorts of data. (And, make no mistake, the study of weather is all about math and physics.)

Also through the glass, you can see one of 122 local National Weather Service offices that dot the nation, where the local forecast is parsed and communicated to news outlets. A third monitor-filled room is the hazardous-weather testing area, where new technology is constantly being evaluated. You'll also see an office reserved for Oklahoma State University, where agriculture department authorities confer with weather experts.

The tour leaves the building twice. You'll go out behind the building and see about 50 vehicles the Weather Center uses to gather storm information (unless they're all out doing that, which they will be if you go on a stormy day). The Weather Center doesn't chase storms down and photograph them. It forms a perimeter around them with these various vehicles (some of them hail-dented), and their instruments record data.

The dual polarization radar developed here was a "huge leap forward" for forecasters, Kloesel says. It sees precipitation in three dimensions, which means forecasters can measure the size of raindrops and tell the difference between ice and liquid.

The other outdoor portion of the tour is on the roof.

"Our entire roof is a classroom," Kloesel says, pointing out instruments amid a garden of native grasses and purple flowers, all chosen for the green roof because they never need watering. Little five-note beeps are emitted by a sodar (like radar, only using sound) machine that bounces sound signals off all those waves of weather we saw on the sphere in the lobby.

DON'T MISS

Several golf ball-shaped structures on campus make up the station's weather radar. From this roof, meteorologists have seen tornadoes for five years in a row. The building has two fully equipped shelters.

IF YOU GO

Tours are held Mondays, Wednesdays and Fridays at 1 p.m., and must be arranged two to four weeks in advance. For security reasons, foreign nationals are asked to provide their passport information. For more information, call 1-405-325-1147 or go online to www.nwc.ou.edu/tourdetails.php.