The Terrain Induced Rotor Experiment (T-REX) was conducted during March and April 2006, during which time 102 radiosondes were launched using a fix sounding system located near Independence, California. T-REX 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 upwind radiosonde launches, from the California Central Valley, used to help predict the onset of events likely to produce rotors on the lee side of the Sierra Nevada Mountain Range. Soundings were also launched in the Owens Valley from an Integrated Sounding System (ISS).