BOULDER, Colo. - Scientists have completed the first phase of a two-year, $12 million project to study tornadoes in the central United States, encountering only one twister as they stalked storms in a nine-state region with an army of 120 researchers and 50 vehicles.

Researchers hope to use the program to learn more about how tornadoes form and the damage they can cause, while improving the lead times on tornado warnings to the public.

On Wednesday, they discussed their efforts during the first phase of the project.

In a below-average tornado season, it was nearly a month before scientists got a first-hand look at a tornado; one touched down in Wyoming June 5.

The twister in southeastern Wyoming had nearly ideal conditions for study - it was isolated and moved in a relatively straight line, said Josh Wurman of the Vortex2 project.

"Nature threw us a very slow pitch that day," he said.

Because researchers had detected tornado conditions, they got to the scene 20 minutes before the twister formed, which gave them time to gather key information that will help them understand what causes such storms.

"That's the prize that we're after," said David Dowell, a scientist with the National Center for Atmospheric Research in Boulder.

One group of researchers got within about a mile of the tornado, and some unmanned instrument clusters were closer, although Wurman said the tornado may not have passed directly over them as they had hoped.

The project name, Vortex2, stands for Verification of the Origins of Rotation in Tornadoes Experiment-2 The is funded primarily by the National Science Foundation and the National Oceanic and Atmospheric Administration.

Vortex2 focused on Minnesota, South Dakota, Iowa, Nebraska, Wyoming, Colorado, Kansas, Texas and Oklahoma.

Equipment used during the study included multiple types of radar, mobile mesonets, mobile ballooning systems, unmanned aircraft, tornado pods and particle probes.

The instruments measure wind, temperature, humidity and pressure, and two cameras record video. They're designed to survive a direct hit, but even if they're destroyed, data would likely survive because it's stored in a heavy waterproof case, said Wurman, president of the Center for Severe Weather Research.

Although they saw just one tornado first-hand, Wurman and other researchers say the first phase of the project was a success.

They tracked and studied numerous thunderstorms that didn't spawn tornadoes, which they said will help them figure out why some weather systems produce twisters and others don't.

They also learned how to quickly deploy their army of 120 researchers and 50 vehicles, some equipped with mobile radar.

"I'm pretty confident now that we've debugged the system," said Roger Wakimoto, senior scientist with the National Center for Atmospheric Research. "It was almost like a military operation."

The field study resumes in May 2010.