A lunar tidal model similar to that of Forbes <1982> is used to investigate the effects of changes in background zonal winds on the structure of the lunar tide in the upper atmosphere. It is found that changes in the winds have a greater effect than changes in the background temperature profile with latitude. Observed changes in the structure of the lunar tide from year to year at Saskatoon may be explained by introducing stratospheric warmings into the model. The addition of an associated mesospheric cooling gives an even better fit to the observed phase data. It is also seen that northern hemisphere warmings are predicted to give considerable amplitude changes in southern hemisphere lunar tides. It is expected that much of the difficulty in measuring lunar tides in the upper atmosphere is due to changes in the tidal parameters at these levels brought about by variations in the underlying atmosphere.¿ 1997 American Geophysical Union