Simulating the Diurnal Evolution of Temperature and Wind over Sloped Terrain: A Case Study in Eastern Snake River Plain, Idaho

Accurately predicting the diurnal cycles of temperature and wind over mountainous terrain is critical for many applications, yet it remains a challenge. This study evaluates the Weather Research and Forecasting (WRF) model’s ability to capture the diurnal cycles of temperature and wind over the Eastern Snake River Plain (ESRP) in Idaho, USA. The baseline WRF simulation reproduces the general diurnal cycles of temperature and wind but shows a significant nighttime warm bias, which is associated with weaker nocturnal drainage flows and an earlier morning transition. Sensitivity tests show persistent nighttime warm bias and trade-offs in model tuning. We also investigate whether large-eddy simulations (LES) can reduce nighttime temperature biases. Compared to mesoscale runs with a 1-km horizontal resolution, LES runs with horizontal resolutions of 125 m and 25 m using the Nonlinear Backscatter and Anisotropy (NBA) model show smaller nighttime temperature biases. Analysis of the potential temperature budget reveals compensating effects of dynamics and radiation in controlling the nocturnal temperature evolution. These results underscore the challenges of modeling heat transfer over complex terrain and suggest that improved subgrid-scale turbulence parameterizations can help address nighttime temperature biases.