ABSTRACT
A new mesoscale version of the regional forecast system became operational at the Canadian Meteorological Centre on 18 May 2004. The main changes to the regional modelling system include an increase in both the horizontal and vertical resolutions (15-km horizontal resolution and 58 vertical levels instead of 24-km resolution and 28 levels) as well as major upgrades to the physics package. The latter consist of a new condensation package, with an improved formulation of the cloudy boundary layer, a new shallow convection scheme based on a Kuo-type closure, and the Kain and Fritsch deep convection scheme, together with a subgrid-scale orography parametrization scheme to represent gravity wave drag and low-level blocking effects. The new forecast system also includes a few changes to the regional data assimilation such as additional radiance data from satellites.
Objective verifications using a series of cases and parallel runs, along with subjective evaluations by CMC meteorologists, indicate significantly improved performance using the new 15-km resolution forecast system. We can conclude from these verifications that the model exhibits a marked reduction in errors, improved predictability by about 12 hours, better forecasts of precipitation, a significant reduction in the spin-up time, and a different implicit-explicit partitioning of precipitation. A number of other features include: sharper precipitation patterns, better representation of trace precipitation, and general improvements of deepening lows and hurricanes. In mountainous regions, several aspects are better represented due to combined higher-resolution orography and the low-level blocking term.
