Atmospheric River Analysis and Forecast System (AR-AFS): Improving Forecasts of Atmospheric Rivers on the US West Coast

Atmospheric rivers (ARs) are narrow belts of concentrated atmospheric moisture which are responsible for the majority of extreme rainfall in the western North America. The series of strong ARs from December 2022 to March 2023 brought extreme rainfall and serious hazards in the western United States. AR Reconnaissance (ARR) campaigns plan and deploy aircrafts over the northeast Pacific to collect observations to improve AR forecasts. A high-resolution regional model, Atmospheric River Analysis and Forecast System (AR-AFS), has been developed to provide numerical guidance for AR forecasts and ARR. AR-AFS is based on the FV3 dynamical core and uses initial and boundary conditions from the NCEP operational Global Forecast System version 16 (GFSv16). It provides 5 day forecasts, and has 64 vertical layers and a fine horizontal resolution of 3 km over the Northeast Pacific and western North America. In order to study the dropsonde impact on AR forecasts with AR-AFS, during the 2022-2023 ARR campaigns, two sets of experiments were carried out using initial and boundary conditions from GFSv16 control and denial experiments which use or deny the dropsonde data for the data assimilation in GFSv16. Given the important role of atmospheric and surface processes in the numerical simulations, we examined the effects of different physical schemes from the Common Community Physics Package (CCPP) on the performance of AR-AFS. The summary of ARR data impact experiments and experiments on AR-AFS physics will be presented at the conference.