Lidar observations of noctilucent clouds (NLCs) have shown that the mean diurnal variations of the NLC altitude and backscatter ratio are dominated by semidiurnal components that are at odds with previous model simulations using mean tidal temperature variations. Measured tides, however, exhibit a strong day-to-day variability so that, as a consequence of the highly nonlinear response of NLC models to temperature changes, the mean diurnal NLC variation cannot be obtained from the mean diurnal temperature variation but has to be simulated by averaging over NLC samples computed from individual diurnal temperature variations. Therefore a simple model of tidal variability based on means and standard deviations of the diurnal and semidiurnal temperature amplitudes and phases is set up so that samples of the diurnal temperature variation and corresponding NLC samples can be computed. The resulting mean diurnal variations of the NLC altitude and backscatter ratio show a good overall agreement with the observed variations and clearly reflect the strong semidiurnal components. Discrepancies between observed and simulated results can be attributed at least partly to deficiencies of the tidal variability model which, in particular, does not take into account any coherence between tidal and planetary wave-associated temperature variations. ¿ 2001 American Geophysical Union