Observations and High-Resolution Rapid Refresh Model Verification of the Lake Michigan Warm-Season Marine Atmospheric Boundary Layer Weather and Forecasting

This study investigates the structure and evolution of the warm-season Lake Michigan marine atmospheric boundary layer (MABL) and associated lake-breeze circulations. Four missions were conducted during the 2023 and 2024 warm seasons, with 55 total rawinsondes launched to collect vertical profiles of temperature, humidity, and wind and document MABL variability near Lake Michigan’s western shoreline. The observations were further used to assess the High-Resolution Rapid Refresh (HRRR) model’s ability to resolve boundary layer structures. The observations demonstrate the early warm-season Lake Michigan MABL is characterized by strong, shallow, and stable temperature inversions, whereas the late warm-season MABL exhibits a deeper, neutrally buoyant boundary layer. MABL profiles across the warm season also exhibit little thermodynamic diurnal evolution or spatial variability across moderate lake surface temperature gradients. Wind observations documented notable kinematic shifts throughout the MABL associated with the development of lake-breeze circulations as early as 1100 CDT (1600 UTC). Verification of HRRR analyses and forecasts demonstrated the model’s inability to resolve sharp thermodynamic gradients immediately above the lake surface and atop the MABL. These results improve our understanding of the warm-season MABL structures across the Great Lakes where in situ observations are sparse and highlight the challenge in accurately representing those structures in high-resolution numerical weather prediction models.