Production and advection of precipitating water in a prescribed, time dependent flow is investigated by means of a simple 2D model in order to predict the periodical behaviour of rain rate and pressure which was observed in the Po valley during IOP8 of MAP. The (x,z,t)-dependent wave perturbations on wind and temperature fields were derived from a linear stability analysis and are superimposed on z-dependent background fields. The wave influence
on the hydrometeors production and advection is discussed
