A forty-year gridded meteorological forcing dataset spanning the water years 1984 to 2023 (October 1<sup>st</sup> to September 30<sup>th</sup>) was compiled for the Reynolds Creek Experimental Watershed (RCEW) in southwest Idaho, USA. This Reynolds Creek Long-Term (RCLT) dataset consists of hourly, 10-meter resolution grids of air temperature, vapor pressure, precipitation mass and phase, incoming shortwave and longwave radiation, visible and infrared snow albedo, and wind speed and direction. These variables were interpolated and calculated from hourly measurements from the dense meteorological station network within the mountainous 239 km<sup>2</sup> RCEW, which contains elevations that span the historical winter rain-to-snow transition. The observations are foundational for many ecological and hydrological Land Surface Models (LSMs) used in research and operational applications. Additionally, an example use case is presented in which we show how the snow-dominated area of the basin has evolved over the data record. This 13 TB dataset, stored in cloud-optimized Zarr format, enables future model development, benchmarking, and uncertainty analyses of existing models, independent validation of gridded atmospheric reanalysis datasets, and novel investigations of hydroclimatic variability across snow-dominated semi-arid environments. Data access is available via the following repository: <a href="https://doi.org/10.15482/USDA.ADC/30199954" target="_blank" rel="noopener">https://doi.org/10.15482/USDA.ADC/30199954</a> (Hedrick et al., 2025).