Harmonic Analysis technique has been employed in predicting the hourly air temperature variations over Lagos and Abuja, Nigeria. The variations in hourly air temperatures over the two stations are periodic and thus have strong tendency of being repeated the next day, if all other atmospheric variables are constant. It was observed that the variation in hourly air temperature in the two stations is dominated by the first harmonic, thus it fluctuates by one cycle with a period of 24 hours. Invariably, harmonic equations could be applied to hourly temperature prediction even on a large scale data. The maximum hourly air temperature occurred two hours on the average after the maximum solar irradiance has occurred in each station. It was found that the temperature of the air at a particular hour is dependent on that of the previous hour.