The paper gives the outline of a 'meteorological preprocessor' for air pollution modeling. It is shown how significantly more information can be extracted from routinely available measurements than the traditional Pasquill stability classes and power law wind speed profiles. Also it is shown how additional special measurements--if available--can be accommodated. The methods are primarily intended for application in generally level, but not necessarily homogeneous terrain. The improved characterization of the state of the planetary boundary layer allows a more modern and probably more accurate description of diffusion. The paper is an extended version of an introductory paper presented during the 'Workshop on Updating Applied Diffusion Models' in Clearwater, Florida, January 1984.