Using a standalone radiation model developed by Fu and Liou, we examine the contributions of the observed seasonal variation in clouds, water vapor, and surface albedo to the radiative damping of the seasonal variation of surface air temperature (SAT). We focus on mid and high latitudes regions, where the seasonal cycle of SAT is largest. We find that the radiative damping of the seasonal cycle of SAT is generally 2-5 times larger than expected from the Stefan-Boltzmann law. This is mainly due to the large seasonality of cloud cover, which exerts a strong negative feedback on SAT. The seaonal variation of water vapor reduces the radiative damping of SAT by 3-5 W/m2 everywhere, consistent with a positive water vapor feedback. Surface albedo feedback is also positive in the context of the seasonal cycle, though generally weaker than water vapor feedback. Finally, we compare the radiative damping of SAT to the other terms in the surface air heat budget to evaluate the importance of radiative damping in determining the observed amplitude and phase of the seasonal cycle of SAT.