Communications to and from a launch vehicle during ascent are of critical importance to the success of rocket-launch operations. During ascent, the rocket's exhaust plume causes significant interference in the radio communications between the vehicle and ground station. This paper presents an improved line of sight: a lower-collision-frequency microwave signal attenuation model based on the plume chemistry, microwave path, and the cross section for momentum transfer. The proposed model considers the combustion products in the exhaust plume, ambient air entrainment downstream of the nozzle, and a plasma attenuation model to estimate the total radio-frequency signal attenuation. The proposed model is benchmarked against measurements of signal attenuation through an exhaust plume in the 12.4 to 18 GHz frequency range.