Downstream evolution and coastal-to-inland transition of landfalling lake-effect systems

The distribution and intensity of lake- and sea-effect (hereafter lake-effect) precipitation are strongly influenced by the mode of landfalling lake-effect systems. Here, we used idealized large-eddy simulations to investigate the downstream evolution and coastal-to-inland transition of two lake-effect modes: 1) a long-lake-axis-parallel (LLAP) band generated by an oval body of water (hereafter lake; e.g., Lake Ontario) and 2) broad-coverage, open-cell convection generated by an open lake (e.g., Sea of Japan). Under identical atmospheric conditions and lake-surface temperatures, the oval lake generates a LLAP band with heavy precipitation along the midlake axis, whereas the open lake generates broad-coverage, open-cell convection with widespread, light accumulations. Over the oval lake, the LLAP band features a thermally forced and diabatically enhanced cross-band secondary circulation with convergence and ascent over the midlake axis. Downstream of the lake, flanking airstreams that avoid lake modification merge beneath the band where they experience sublimational cooling, producing a cold pool. At the upstream edge of the cold pool, a coastal baroclinic zone forms. Above this zone, ascent and hydrometeor mass growth are maximized, resulting in an inland precipitation maximum due to subsequent hydrometeor transport and fallout. Over the open lake, individual open cells grow larger and stronger with overwater extent, but a convective-to-stratiform transition begins at the coast. Here, convective vigor decays, mesoscale ascent begins, and enhanced hydrometeor growth results in an inland precipitation maximum. These results highlight variations in the coastal-to-inland transition of lake-effect systems that ultimately influence the distribution and intensity of lake-effect precipitation. SIGNIFICANCE STATEMENT: Lake-effect snow impacts many urban and rural communities, disrupting transportation and commerce, but benefiting regional winter-sports economies. Using high-resolution computer modeling with simple lake shapes, we simulated two common types of landfalling lake-effect storms: 1) intense bands that sometimes produce extreme but highly localized snowfall and 2) scattered cells that typically generate widespread lake-effect snow showers. Our analysis describes how these distinct storms transform as they move inland, affecting the distribution and intensity of snowfall over downstream communities. Knowledge of this transformation is important for understanding lake-effect storms and improving forecasts of lake-effect snowfall.