Stalled Improvement in a Numerical Weather Prediction Model as Horizontal Resolution Increases to the Sub-Kilometer Scale

This study evaluated the performance of a regional weather prediction model. The horizontal resolution is increased to the sub-kilometer scale in a series of experiments over areas of Japan through the summer or winter seasons of 2015-2016. The performance improves less when increasing the horizontal resolution from 2 km to 1 km or 500 m than it does from 5 km to 2 km, especially when topography and ice microphysics are less relevant. Although the velocity and magnitude of updrafts, cloud size, and convection in the boundary layer indeed change with the horizontal resolution, these differences turn out to have little impact on the model performance.