This paper proposes a method to control the data rate of an Earth Space link using VCM at Ka band based on the use of meteorological forecasts. Specifically, a probabilistic model of propagation impairments forecast has been developed from the analysis of rain rate measurements and outputs of the Météo-France short-range probabilistic forecast model. The approach is validated against propagation data acquired on a GEO to ground link and applied to the case of a LEO data down link using VCM, where it is shown to outperform significantly the data rate achievable using a purely statistical margin, while keeping the same availability target.