A complete operational method for quantitative precipitation forecasting (Q.P.F.), is developed by combining the technique for determining large scale vertical velocities by Penner with one for determining precipitable water content using 1000–500-mb thickness lines and the Godson precipitation rate formula. Methods are included for taking into account the effects of initial unsaturation, topography, release of latent heat during condensation, friction, release of potential instability and height of cloud base. A case study is presented to illustrate the results of the method and an example is given of a complete Q.P.F. computation.