The Terrain Induced Rotor Experiment (T-REX) was conducted during March and April 2006, during which time 87 radiosondes were launched using a mobile sounding system at three locations (Visalia (71), Madera (9) and Delano (7)) in the California Central Valley. TREX is the second phase of a coordinated effort to explore the structure and evolution of atmospheric rotors, which typically occur parallel to, and downstream from, mountain ridge crests. The first phase was a project conducted in 2004 called the Sierra Rotors Project. Both phases included downwind radiosonde launches from the central valley, used to help predict the onset of events likely to produce rotors on the West side of the Sierra Nevada Mountain Range. In order to capture the structure of the rotors, additional instruments were set up in California's Owens Valley.