Turbulence measurements of the three dimensional wind components were collected by an instrumented research aircraft on 7 days in August 1976. These aircraft flights were conducted as part of the Regional Air Pollution Study (RAPS) urban boundary layer field program in St. Louis, Missouri. The focus of this research was to determine the magnitude and variation of characteristics of vertical velocity fluctuations in the afternoon convective boundary layer from data obtained at 150 m above ground. The vertical velocity time series for 22.5 km length segments were evaluated to obtain quantitative information on upward and downward turbulent motions in the urban convective boundary layer. Results of analysis revealed that vertical velocity distributions for both urban and nonurban segments displayed positive skewness and negative mode. In addition, the results of comparisons of the size of the largest updraft, convective boundary layer height, and the vertical velocity spectral peak wavelength are presented.