We use Kokkos, a C++ library for on-node parallelism, to achieve a performance-portable implementation of HOMME, the atmosphere component of the Earth Energy Exascale System Model. The increasing diversity of high-performance computing (HPC) architectures and the demand for higher resolutions create new challenges when writing efficient code. With Kokkos, we obtain a single code base that performs well on current HPC platforms and enables portable performance to future HPC architectures.