HPSF Conference 2025

At NOAA, much of the code for numerical weather prediction (NWP) and operational weather forecasting is built upon Fortran, into which decades of scientific research knowledge and expertise has been invested. Therefore, moving away from Fortran and potentially breaking what has been a highly reliable system for many years is a significant challenge.
To demonstrate new methods to modernize NOAA’s NWP models, Kokkos was selected due to its ability to work across multiple GPUs and CPUs with a single source code and the presence of the Fortran Language Compatibility Layer (FLCL), easing development of the interface between Fortran and C++ Kokkos kernels. As a first step, the YSU Planetary Boundary Layer (PBL) scheme was chosen as the target and a prototype with Kokkos was developed, tested, and performance benchmarked. In this presentation, we report the performance of this new Kokkos-enhanced Fortran code on CPU and an Nvidia GPU, the challenges of the C/Fortran interface, potential future prospects for the use of Kokkos at NOAA, and overall lessons learned from this project for anyone else interested in using Kokkos with existing Fortran source codes.