Verification of Marine Boundary Layer Forecasts in Atmospheric River Environments using Dropsonde Observations

Investigations of the marine boundary layer influence on the development and evolution of atmospheric rivers (ARs) have historically been limited due to the absence of high-resolution, quality-controlled observations of the lower atmosphere in AR environments. In recent years, the Center for Western Weather and Water Extremes (CW3E) AR Reconnaissance (AR Recon) program has utilized dropsondes to gather high-resolution vertical profiles of temperature, wind, and moisture within the marine boundary layer beneath ARs. In this study, AR Recon dropsonde observations are used to verify WRF model forecasts of marine boundary layer dynamics, such as the depth of the boundary layer, the height and strength of the low-level jet, and vertical profiles of temperature and moisture. Five AR events from water year 2023 are simulated using WRF ensemble forecasts constructed to represent uncertainty in the marine boundary layer, including a multiphysics approach which varies the PBL parameterization scheme between ten ensemble members. Preliminary results indicate that, while most PBL schemes underestimate the height of the marine boundary layer compared to dropsonde observations, ensemble members using the GBM and UW schemes tend to diagnose the lowest PBL heights over the ocean surface, while those using the QNSE-EDMF and ACM2 schemes are associated with the highest. Further analyses of these experiments will be utilized to identify key sources of error and uncertainty in the structure of the marine boundary layer during AR events, with the goal of improving the prediction of high-impact weather associated with ARs.