A numerical analysis is conducted to investigate the performance degradation of iced airfoils in terms of meteorological parameters. Reference ice accretion shapes are taken from NASA's icing wind tunnel test results. Ice accretion shape and aerodynamic performance of the airfoil are numerically calculated under the same conditions as those used in the tests, and response surface equations are generated based on the results. The response surface models are applied to the conditions specified in Federal Aviation Regulations, appendix C of part 25, and the changes in aerodynamic coefficients are investigated. The areas of most significant lift and drag performance degradation overlap. The lift coefficient plunges more than 50% under temperatures greater than −10°C and LWC greater than 2g/m3. Under the same conditions, the drag performance greatly decreases as well. On the other hand, the moment coefficient greatly decreases under temperatures of less than −40°C and greater MVD. Changes in free stream speed yield little effect on moment performance compared to lift and drag. Within the bounds specified in the present study, the effects of exposure time are insignificant.