This paper investigates the effect of different physics parameterizations on summertime precipitation as simulated by the Pennsylvania State University-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM4). The period of simulation is July 1979. The control simulation is carried out with a standard version of the MM4 including a simplified Kuo scheme, a bulk boundary-layer representation, and a force-restore scheme for ground temperature calculation. The parameterizations tested are a modification of the standard MM4 Kuo scheme, which imposes storage and slow release of condensation heat, an explicit moisture scheme, a version of the Arakawa-Schubert scheme, and a relatively sophisticated hydrology package. The standard MM4 strongly overestimates precipitation over mountainous terrain and, in particular, it produces an excessively large number of gridpoint precipitation events in excess of several centimeters (“numerical point storms” or NPS's). These are due to intense vertical m... Abstract This paper investigates the effect of different physics parameterizations on summertime precipitation as simulated by the Pennsylvania State University-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM4). The period of simulation is July 1979. The control simulation is carried out with a standard version of the MM4 including a simplified Kuo scheme, a bulk boundary-layer representation, and a force-restore scheme for ground temperature calculation. The parameterizations tested are a modification of the standard MM4 Kuo scheme, which imposes storage and slow release of condensation heat, an explicit moisture scheme, a version of the Arakawa-Schubert scheme, and a relatively sophisticated hydrology package. The standard MM4 strongly overestimates precipitation over mountainous terrain and, in particular, it produces an excessively large number of gridpoint precipitation events in excess of several centimeters (“numerical point storms” or NPS's). These are due to intense vertical m...