A study is made oi* me impact of enhanced horizontal resoiution and cumulus parameterization on the Simulation of precipitation by a numerical weather prediction (NWP) model. In particular theoretical, observational and modelling aspects related to a mesoscale NWP model are considered. In models of this scale precipitation is formaüy separated into an unresoived convective part and a grid-resolvable part, and there is a need for an appropriate method to parameterize the unresoived component. The study falls into three distinct, but related parts.