Push a parcel of air over a mountain and watch geography make weather. This lifts your air dry-adiabatically to the cloud base, integrates a proper saturated adiabat over the summit — the lapse rate is recomputed at every step from the temperature and pressure, not assumed — rains the water out, and drops the parcel down the far side to show you exactly why one flank is a rainforest and the other is a desert.