Approximately 2,000 zero-lift, double-theodolite pilot balloon observations made at Oak Ridge, Tenn., are analyzed in order to study low level air trajectories over hilly terrain. Paths of air parcels are found to fall into characteristic groups, depending on wind speed and stability conditions. Eddy patterns for these groups are determined, and these are found to resemble similar patterns determined for different types of terrain. The properties of low level air flow, particularly of vertical velocity patterns, are displayed in various ways. Slope winds due to thermal-dynamical effects appear to contribute more to these patterns than does a purely mechanical lifting effect. Abstract Approximately 2,000 zero-lift, double-theodolite pilot balloon observations made at Oak Ridge, Tenn., are analyzed in order to study low level air trajectories over hilly terrain. Paths of air parcels are found to fall into characteristic groups, depending on wind speed and stability conditions. Eddy patterns for these groups are determined, and these are found to resemble similar patterns determined for different types of terrain. The properties of low level air flow, particularly of vertical velocity patterns, are displayed in various ways. Slope winds due to thermal-dynamical effects appear to contribute more to these patterns than does a purely mechanical lifting effect.