According to the US Department of Energy, the main equipment used to predict tornadoes is the Doppler radar system. Doppler radar can measure wind velocity, direction of the wind inside the storm and the predicted rainfall.
Storm chasers and tornado investigators have developed mobile Doppler radar devices that can be mounted on the outside of vehicles. The investigators travel to the locations of the tornadoes in these vehicles and can make observations about an approaching storm. Several mobile units can be placed a few miles away from one another in order to create extremely accurate observations concerning wind fields and data around a tornado.