The use of EHF and SHF systems operating above 20 GHz is becoming increasingly popular for high-capacity communication systems. This popularity is driven by a number of factors, the most common being the congestion at lower-frequency bands and the potentially high capacities available. One of the main disadvantages of using these higher frequencies is that the attenuation caused by atmospheric effects can become large. Attenuation caused by clouds, rain and atmospheric gases become very large. In this paper an attenuation forecasting algorithm is demonstrated with a 20.7 GHz satellite beacon measured at two locations separated by 7.5 km. The algorithm deliberately uses data-sets that are in common use and represents the gains available with current technologies, without the use of high-resolution Numerical Weather Prediction systems. The model is compared to 20.7 GHz beacon measurements made at two sites in the South of England. The model demonstrates statistics that match those of the beacon and the timeseries of the model and the beacon also match well. The diversity gain demonstrated by the two locations is also modelled well using this technique. This makes the system ideal for modelling earth-space propagation at EHF and SHF frequencies.