A Case Study of the Simultaneous Development of Multiple Lake-Breeze Fronts with a Boundary Layer Forecast Model

A fast-response boundary layer forecast mesoscale model has been used to simulate and to study the complex three-dimensional circulation associated with lake breezes in southwestern Ontario. The simultaneous development of lake-breeze fronts, their inland progression, and their confluence with each other were numerically simulated. The progression of a dominant lake breeze influenced and inhibited the penetration inland of other lake-breeze fronts. Modeled flow and vertical velocity distributions were in good agreement with satellite cloud pictures and meteorological data from a special mesoscale network of towers. Of particular interest were regions of strong convective activity at the confluence of lake-breeze fronts and an area of descending motion over land identified by a cloud-free area. The former is explained by the triggering mechanism of lake-breeze-induced convergence and ascending motion; the latter may be due to dynamically induced subsidence in a relatively low-lying area surrounded by strong convection. The low-level divergent-flow boundary associated with this subsidence was also noted as a convection-enhancing mechanism by its interaction with the nearby lake-breeze-induced convergence line.