A Preliminary Assessment of the High-Resolution Rapid Refresh Model’s Ability to Predict the Great Lakes Lake-Breeze Front and Marine Atmospheric Boundary Layer

The Great Lakes region's climate is heavily influenced by air-sea interaction. Because of the high specific heat capacity of water relative to the land surface, the Great Lakes respond slower to surface heating and cooling. In the spring and summer, this is manifested by cooler water temperatures relative to the land surface, such that the daytime, warm-season marine atmospheric boundary layer (MABL) is characterized by cooler, more dense and stable air relative to the continental airmass. If the temperature difference between these airmasses is large enough, the boundary between them – the lake-breeze front – can progress inland during the local afternoon hours. Assessing the location of the lake-breeze front is necessary to accurately depict and forecast sensible weather in the Great Lakes region, especially for major metropolitan areas such as Chicago, Milwaukee, Detroit, Cleveland, and Buffalo along the Great Lakes’ shorelines.

This research seeks to determine the ability of the High-Resolution Rapid Refresh (HRRR) mesoscale model to accurately predict the lake-breeze front’s structure and evolution and to faithfully represent the MABL behind it, with a specific focus on the lake-breeze front on Lake Michigan’s western shore. First, a model-based lake-breeze front detection algorithm based on horizontal on changes in temperature, stability, and wind shear across the lake breeze boundary is developed and evaluated for lake-breeze front cases from late summer 2022 and spring/summer 2023. Feature-based verification metrics will be used to assess the HRRR’s forecast skill for lake-breeze front propagation and evolution. Further, to aid in evaluating the HRRR’s ability to faithfully represent the MABL, radiosonde and rawinsonde observations will be collected during two field excursions in late spring and mid-summer 2023 from the nearshore Lake Michigan waters. HRRR-derived vertical soundings will be evaluated against the collected over-lake observations using standard forecast evaluation metrics such as bias and root-mean squared error. If a model-based approach to lake-breeze forecasting is shown to be skillful, the results of this research will help improve Great Lakes warm season coastal forecasting. This is particularly important considering the potential for the lake breeze to initiate convection, modulate stability, and influence large-scale convective systems.