Heavy precipitation simulation in non-hydrostatic CESM modeling over the Western US

This study evaluates the ability of the Community Earth System Model version 2 (CESM2), with the non-hydrostatic Model for Prediction Across Scales (MPAS) dynamical core coupled to the Community Atmosphere Model (CAM) to simulate heavy precipitation over the western US during five seasonal simulations in consecutive years. We configure a high-resolution 3 km mesh over the western US with remaining global domain at 60 km grid spacing. We analyze heavy precipitation, moisture transport, and thermodynamic and dynamic characteristics, comparing simulated rainfall and snowfall with reanalysis and observations for the Northwest (Oregon/Washington) and Southwest (California) regions during heavy precipitation days. The model reasonably captures extreme precipitation spatial features over complex terrain, with 3 km resolution significantly improving agreement with observations. While water vapor transport patterns generally match MERRA-2 reanalysis over the coastal west, some discrepancy exists especially over the California region. Overall, CAM-MPAS demonstrates the critical role of high resolution in improving heavy precipitation, rainfall and snowfall representation over complex terrain, showing promise for studying extreme storms and associated hydrological impacts.