The development of a new lightning frequency parameterization and its implementation in a weather prediction model Based on a straightforward physical model a new lightning parameterization has been developed: A two plate capacitor represents the basic dipole charge structure of a thunderstorm which is charged by the generator current and discharged by lightning. In this approach the generator current as well as the discharge strength are parameterized using the graupel mass field. If these two quantities are known and if the charging and discharging are in equilibrium then the flash rate is uniquely determined. This approach remedies shortcomings of earlier theoretical approaches that relate the flash rate e.g. to generator power. No distinction is made between intracloud and cloud to ground discharges. In order to test this approach polarimetric radar data were used from which the graupel distribution in observed thunderstorms could be inferred. The lightning activity was detected using the LINET network. The comparison between theoretically predicted and measured flash rates is encouraging: Over a wide range of flash rates the theoretical approach yields accurate results for isolated thunderstorms. Two existing parameterizations which only use the depth of the clouds as predictor produce substantially less accurate forecasts ...