A Preliminary Assessment of the HRRR’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 and the offshore component of the synoptic-scale, near-surface horizontal wind weak enough, the boundary between them – the lake-breeze front – can progress inland during the local afternoon hours. Assessing the lake-breeze front’s location 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 faithfully represent the MABL behind it. First, a model-based lake-breeze front detection algorithm derived from computed second-order horizontal partial derivatives of planetary boundary layer (PBL) height is developed and evaluated, following which the HRRR’s forecast skill for lake-breeze front propagation and evolution is assessed for 2022-23 warm-season lake-breeze front events. Preliminary results suggest high skill for lake-breeze front initiation but variable skill for lake-breeze front propagation and evolution as compared to observations.

It is hypothesized that the HRRR’s depiction of the Lake Michigan MABL, influencing the airmass properties behind the lake-breeze front, plays a significant role in the forecast skill of the lake-breeze front’s propagation and evolution. To test this hypothesis, Windsond rawinsonde observations from over Lake Michigan east of Milwaukee, WI during summer 2023 are collected and analyzed. The collected observations and preliminary model evaluation results will be presented during the talk. The results from these and planned future field excursions will advance understanding of warm-season MABL structure over the Great Lakes, how it relates to lake-breeze front propagation, and how faithfully the HRRR depicts these features.