Modeling the Urban and Lake-induced Boundary-Layers for the Greater Toronto Area

An integrated experimental sub-kilometer atmospheric modeling system with grid-spacings of 1 km and 250 m using hourly forcing of lake-surface temperatures and including urban processes has been developed at the Meteorological Service of Canada (MSC) in order to provide more accurate weather forecasts at the city scale. A real-time forecasting system has been designed over the Greater Toronto Area (GTA) facing the Lake Ontario, and has provided forecasts for the last year and in particular during the Pan-American and para-Pan American games (TO2015, sport events through the region during summer 2015). Surface physical processes and turbulent fluxes piloting boundary-layer evolution are provided with the Town Energy Balance (TEB) model for the built-up covers and with the Interactions between the Surface, Biosphere, and Atmosphere (ISBA) land surface model for the natural covers. Surface temperatures for the Great Lakes are prescribed using 2-km hourly output from an ocean model. In this study the ability of the system to capture the urban boundary-layer features and its interactions with the lake-breeze patterns for several conditions will be presented. Based on the dense observational network efficient during summer 2015, several aspects of the model performance and limitations will be discussed. Results on the newly developed thermal stress indices