The three-dimensional wind field in the vicinity of the jet stream is defined with the aid of four parameters: mean wind speed and direction, thickness, and mean altitude of the Layer of Maximum Wind (LMW). Routine methods of analysis of these quantities are discussed in view of the reliability of available wind data, and a statistical treatment of these quantities reveals the mean horizontal and vertical structure of the LMW. Forecasts of the LMW are attempted by means of a grid or “box” method, and a control-line method.