Cloud microphysics is a leading source of error in both regional and global climate models and this limits our ability to understand the Earth’s climate and how it is changing. However a fairly new type of model called a Superdroplet Model (SDM) may improve both regional and global models if it can be made cost-efficient enough. Hence we are introducing a novel version of SDM, called CLEO, and it's key features that make it efficient, especially on very high performance, exascale, computers.